docs(sync): bring SYNC.md in line with owning the store

The document was written against the vendored provider and still said the
storage question was settled that way. Owning the store answered several
of its open questions and deleted others outright, so the corrections are
marked inline the way the rest of the file marks them, rather than
quietly rewritten.

Closed: the Local->Synced migration (account_id is a nullable FK, so
attaching an account is an UPDATE), the recurring-completion model (the
store writes model (a), RECURRENCE-ID overrides sharing the master's
UID), the Auto Backup / cleanUpLists data-loss path, and the lib-recur
version trap. Phase 0's UIDs-at-creation and backup safety are shipped.
The provider-mechanism table is kept as External-mode history rather than
deleted — that code still runs in OpenTasks and tasks.org.

Effort restated: 11.5-15 weeks minus the 2.5-4 owning the store removes,
so roughly 8-11. Also states plainly at the top that no sync code exists
and that ICalendarWriter is the export half of the mapper only.

.forgejo/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,24 @@
+# Kept enabled so anything that doesn't fit the four templates still has a way
+# in.
+blank_issues_enabled: true
+
+contact_links:
+  - name: Translate Agendula
+    url: https://weblate.dev.jeanlucmakiola.de/engage/agendula/
+    about: >-
+      Translations are managed on Weblate, not here — it owns every values-*
+      file, so a hand-edited translation gets overwritten on the next sync.
+      No coding needed: pick or request a language and translate in the browser.
+
+  - name: Contributing guide
+    url: https://codeberg.org/jlmakiola/agendula/src/branch/main/CONTRIBUTING.md
+    about: >-
+      Before opening a pull request: how to build (there's a submodule), where
+      code goes, and the one architectural rule a change is reviewed against.
+
+  - name: Sync sources and scope
+    url: https://codeberg.org/jlmakiola/agendula/src/branch/main/README.md
+    about: >-
+      Agendula is a front-end over the OpenTasks provider, so it works with
+      DAVx5, SmoothSync, DecSync and friends. Google Tasks and Microsoft To Do
+      are out of scope by design — check here before requesting a backend.

.forgejo/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,42 @@
+<!--
+Thanks for contributing to Agendula!
+
+Please skim CONTRIBUTING.md if you haven't:
+https://codeberg.org/jlmakiola/agendula/src/branch/main/CONTRIBUTING.md
+
+Two things it's easy to get wrong:
+  • The one architectural rule — provider column names, `TaskContract`,
+    `ContentResolver` and the authority string never leak above `data/tasks/`.
+  • Don't bump `versionName` / `versionCode`. That bump reaching `main` is what
+    cuts a release, so it belongs only in a release PR.
+-->
+
+### What this changes
+
+
+### Why
+
+<!-- Closes #123 — link the issue this implements or fixes. -->
+
+
+### How it was tested
+
+<!--
+Which of these ran green, and anything you exercised by hand. On-device notes
+are especially useful for UI changes, and for anything touching the provider
+read/write paths (OpenTasks / tasks.org installed).
+
+  ./gradlew lintDebug :app:testDebugUnitTest :app:assembleDebug
+  python3 scripts/check_translations.py
+-->
+
+
+### Checklist
+
+- [ ] `./gradlew lintDebug :app:testDebugUnitTest :app:assembleDebug` passes locally
+- [ ] New domain logic comes with JVM unit tests under `app/src/test/`
+- [ ] Provider details stay inside `data/tasks/`
+- [ ] No `values-*/strings.xml` touched (Weblate owns those; new English strings in `values/` are fine)
+- [ ] `CHANGELOG.md` updated under `## [Unreleased]`, if the change is user-visible
+- [ ] No `versionName` / `versionCode` bump
+- [ ] No planning or design documents committed

.forgejo/workflows/ci.yaml

@@ -37,14 +37,29 @@ jobs:
       - name: Reproducible-release invariant
         run: bash scripts/check_reproducible_release.sh
 
-      # Decide whether anything that affects the app build changed. Docs,
-      # F-Droid metadata and the licence don't, so those PRs skip the SDK +
-      # Gradle work below but still report a green `ci`.
+      # Decide whether anything that affects the app build changed. Docs, store
+      # metadata, licence texts and forge housekeeping don't, so those PRs skip
+      # the SDK + Gradle work below but still report a green `ci`.
       - name: Classify change scope
         id: scope
+        env:
+          # Deliberately a skip-list, not a build-list: a path nobody thought
+          # about defaults to building. Only paths the Gradle build provably
+          # never reads belong here — note that the workflows themselves, the
+          # `.gitmodules` submodule pointer and `scripts/` are *not* in it.
+          SKIP_RE: '(\.md$|^docs/|^fastlane/|^fdroid-metadata/|^design/|^\.(forgejo|gitea)/ISSUE_TEMPLATE/|^\.editorconfig$|^\.gitattributes$|^\.gitignore$|^LICENSE$)'
         run: |
           set -e
           BASE="${{ github.base_ref }}"
+          # Normally the bare branch name; tolerate a full ref, which would
+          # otherwise make the merge-base lookup fail and quietly degrade this
+          # guard into "always build".
+          BASE="${BASE#refs/heads/}"
+          if [ -z "$BASE" ]; then
+            echo "No base branch on this event — running the full build to be safe."
+            echo "code=true" >> "$GITHUB_OUTPUT"
+            exit 0
+          fi
           # Full (not --depth=1) base fetch so the merge-base is present even when
           # the PR branch forked several commits back; a shallow tip has no merge
           # base with a divergent branch and `git diff base...HEAD` aborts.
@@ -58,11 +73,15 @@ jobs:
           fi
           CHANGED=$(git diff --name-only "$MB" HEAD)
           echo "Changed files:"; echo "$CHANGED"
-          if echo "$CHANGED" | grep -vE '(\.md$|^docs/|^fdroid-metadata/|^fastlane/|^LICENSE$)' | grep -q .; then
+          RELEVANT=$(echo "$CHANGED" | grep -vE "$SKIP_RE" || true)
+          if [ -n "$RELEVANT" ]; then
+            # Naming them makes "why did my docs PR build for four minutes?"
+            # answerable from the log alone.
+            echo "Build-relevant changes:"; echo "$RELEVANT"
             echo "code=true" >> "$GITHUB_OUTPUT"
           else
-            echo "code=false" >> "$GITHUB_OUTPUT"
             echo "Docs/metadata-only change — skipping the Android build."
+            echo "code=false" >> "$GITHUB_OUTPUT"
           fi
 
       - name: Setup Java
@@ -72,9 +91,14 @@ jobs:
           distribution: 'zulu'
           java-version: '17'
 
+      # Fully qualified on purpose. Codeberg resolves bare `uses:` refs against
+      # data.forgejo.org, Forgejo's own action mirror — actions/checkout,
+      # setup-java and cache all exist there, but android-actions/setup-android
+      # does not, and the job dies with "repository not found". Gitea's instance
+      # defaults to GitHub, which is why this never surfaced before the split.
       - name: Setup Android SDK
         if: steps.scope.outputs.code == 'true'
-        uses: android-actions/setup-android@v3
+        uses: https://github.com/android-actions/setup-android@v3
         with:
           # Default ("tools platform-tools") drags in the Android Emulator
           # (~300 MB) which the build never uses.

.forgejo/workflows/translations.yaml

@@ -0,0 +1,39 @@
+name: Translations
+
+# Fast, SDK-free parity check for translation resources, so Weblate PRs (which
+# only touch values-*/strings.xml) get quick feedback without the full Android
+# build. The deeper checks still run in CI via lintDebug (ExtraTranslation).
+#
+# Runs on every PR (no path filter) so the required "Translations / check"
+# status is always reported — like the `ci` job. A path-filtered workflow is
+# skipped on unrelated PRs and never posts its status, which leaves that
+# required check pending forever and blocks the merge of any code-only PR into a
+# release/* branch. The check itself is cheap and simply passes when the
+# committed translations are consistent, so always running it costs nothing.
+on:
+  pull_request:
+
+concurrency:
+  group: translations-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  check:
+    runs-on: docker
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Ensure python3
+        run: |
+          if ! command -v python3 >/dev/null 2>&1; then
+            if command -v apt-get >/dev/null 2>&1; then
+              apt-get update && apt-get install -y python3
+            elif command -v apk >/dev/null 2>&1; then
+              apk add --no-cache python3
+            fi
+          fi
+          python3 --version
+
+      - name: Check translation parity
+        run: python3 scripts/check_translations.py

.gitea/workflows/release.yaml

@@ -3,12 +3,18 @@ name: Release — F-Droid repo + Gitea/Codeberg release
 # A release is cut by merging a release branch into main with a bumped
 # versionName (see docs/RELEASING.md). This workflow reads that versionName and,
 # if no matching tag exists yet, runs tests, builds + signs the APK, publishes
-# it to the F-Droid repo, creates the vX.Y.Z tag + Gitea release, and mirrors
-# that release to Codeberg with the signed APK + a SHA-256 checksum as a
+# it to the F-Droid repo, creates the vX.Y.Z tag + Gitea release, and publishes
+# the release on Codeberg with the signed APK + a SHA-256 checksum as a
 # direct-download channel — the tag is an output of the pipeline, not its
 # trigger. Ordinary merges (no version bump) fall through `detect` and do
 # nothing.
 #
+# This file lives in .gitea/workflows on purpose: Codeberg is canonical for git,
+# issues, PRs and releases, but every secret (app key, F-Droid repo key, Hetzner
+# credentials) lives on the self-hosted Gitea instance, and this is the only
+# directory Codeberg cannot see. Contributor-triggerable work lives in
+# .forgejo/workflows and references no secret. See docs/RELEASING.md.
+#
 # A manual workflow_dispatch (from a branch) runs the re-sign-only recovery
 # path: it re-signs the existing F-Droid index with the repo key and re-uploads,
 # without building an APK or creating a release. Used for key rotation / repo
@@ -27,6 +33,14 @@ jobs:
   # whether this push actually cuts a new release (no tag for it yet). Keeps the
   # heavy job from running on every merge to main.
   detect:
+    # Gitea only. The workflow directory split already keeps this file invisible
+    # to Codeberg — Forgejo's lookup is first-match-wins, and .forgejo/workflows
+    # exists — but that only holds while .forgejo/ is non-empty. Move the last
+    # file out of it and Codeberg would fall back to .gitea/workflows and start
+    # running the release pipeline on the contributor-facing runner, with no
+    # secrets. repository_owner differs between the two forges regardless of
+    # URL, proxy or instance rename, so this closes it permanently.
+    if: github.repository_owner == 'makiolaj'
     runs-on: docker
     outputs:
       is_release: ${{ steps.v.outputs.is_release }}
@@ -42,8 +56,16 @@ jobs:
       - name: Resolve version and whether it is a new release
         id: v
         env:
-          TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          API: ${{ github.server_url }}/api/v1/repos/${{ github.repository }}
+          # Tags are read from Codeberg, which is canonical — deliberately NOT
+          # from the Gitea API this workflow runs on. The Codeberg -> Gitea sync
+          # is a push mirror, i.e. `git push --mirror`, which deletes refs the
+          # source does not have. A tag minted here on Gitea is therefore wiped
+          # by the next sync (Codeberg does not have it yet) and only reappears
+          # once the tag push at the end of this workflow propagates back.
+          # Asking Gitea inside that window would report "no tag" for a release
+          # that already shipped, and cut it a second time.
+          # Public repo, so this read needs no token.
+          TAG_API: https://codeberg.org/api/v1/repos/jlmakiola/agendula
         run: |
           set -e
           VERSION=$(grep -oP 'versionName\s*=\s*"\K[^"]+' app/build.gradle.kts)
@@ -65,15 +87,28 @@ jobs:
           fi
           # A tag for this version already existing means the release shipped on
           # an earlier push; do nothing. Absent => this merge cuts the release.
-          STATUS=$(curl -s -o /dev/null -w '%{http_code}' \
-            -H "Authorization: token $TOKEN" "$API/git/refs/tags/v$VERSION")
-          if [ "$STATUS" = "200" ]; then
-            echo "Tag v$VERSION already exists — nothing to release."
-            echo "is_release=false" >> "$GITHUB_OUTPUT"
-          else
-            echo "No tag for v$VERSION yet — cutting the release."
-            echo "is_release=true" >> "$GITHUB_OUTPUT"
-          fi
+          #
+          # Anything other than a clean 200/404 is treated as fatal rather than
+          # as "no tag". A Codeberg outage or a network blip would otherwise
+          # read as absent and re-cut a release that has already shipped —
+          # republishing to F-Droid. Failing here is recoverable; a duplicate
+          # release is not.
+          STATUS=$(curl -s -o /dev/null -w '%{http_code}' "$TAG_API/git/refs/tags/v$VERSION" || echo 000)
+          case "$STATUS" in
+            200)
+              echo "Tag v$VERSION already exists on Codeberg — nothing to release."
+              echo "is_release=false" >> "$GITHUB_OUTPUT"
+              ;;
+            404)
+              echo "No tag for v$VERSION on Codeberg yet — cutting the release."
+              echo "is_release=true" >> "$GITHUB_OUTPUT"
+              ;;
+            *)
+              echo "Codeberg tag lookup for v$VERSION returned HTTP $STATUS." >&2
+              echo "Refusing to guess: treating this as 'no tag' could re-cut a shipped release." >&2
+              exit 1
+              ;;
+          esac
 
   # Releases: build + sign + publish, then mint the tag and Gitea release.
   # Also runs on manual dispatch, where it skips the build and just re-signs and
@@ -360,17 +395,21 @@ jobs:
             -F "attachment=@/tmp/$ASSET" \
             "$API/releases/$ID/assets?name=$ASSET" -o /dev/null -w "asset upload HTTP %{http_code}\n"
 
-      # Mirror the release to the Codeberg mirror as a direct-download channel
-      # for users who don't want F-Droid. Gitea already push-mirrors branches +
-      # tags to Codeberg, but releases aren't git objects so they don't sync —
-      # we create the release there over the API and attach the signed APK plus
-      # a SHA-256 checksum. The APK is identical to the F-Droid one (same app
-      # key), so this adds no trust surface. Best-effort: a Codeberg outage
-      # (it 504s under load) must never fail an already-published F-Droid
-      # release. Needs the CODEBERG_RELEASE_TOKEN secret; skips cleanly if unset.
+      # Publish the release on Codeberg, which is canonical for tags and
+      # releases (see docs/RELEASING.md). Codeberg push-mirrors branches + tags
+      # to Gitea, but releases aren't git objects and don't sync in either
+      # direction — so this step pushes the tag straight to Codeberg and creates
+      # the release there over the API, attaching the signed APK plus a SHA-256
+      # checksum as the direct-download channel for users who don't want
+      # F-Droid. The APK is identical to the F-Droid one (same app key), so this
+      # adds no trust surface. Needs the CODEBERG_RELEASE_TOKEN secret; skips
+      # cleanly if unset.
       - name: Publish release to Codeberg
         if: env.IS_RELEASE == 'true'
-        continue-on-error: true
+        # NOT continue-on-error: this step reported green through 0.2.1, 0.2.2,
+        # 0.3.0, 0.3.1 and 0.3.2 while never once publishing, which is how a
+        # crash-fix release reached F-Droid but not the Codeberg/Obtainium
+        # users who needed it. A broken mirror must fail the release loudly.
         env:
           TOKEN: ${{ secrets.CODEBERG_RELEASE_TOKEN }}
           API: https://codeberg.org/api/v1/repos/jlmakiola/agendula
@@ -399,41 +438,58 @@ jobs:
             sed -i -e '/./,$!d' release-notes.md
           fi
           [ -s release-notes.md ] || echo "_See CHANGELOG.md for ${VERSION}._" > release-notes.md
-          # The push mirror (sync_on_commit) usually syncs the tag to Codeberg
-          # before this step runs. Forgejo 500s on POST /releases with a
-          # target_commitish when the tag already exists — so only pass
-          # target_commitish when we actually need the API to create the tag.
-          TAG_CODE=$(curl -s -o /dev/null -w '%{http_code}' \
-            -H "Authorization: token $TOKEN" "$API/git/refs/tags/$TAG")
-          python3 - "$TAG" "$SHA" "$PRERELEASE" "$TAG_CODE" <<'PY' > cb-payload.json
+          # Push the tag to Codeberg ourselves. Under Codeberg-canonical the
+          # mirror runs Codeberg -> Gitea, so waiting for a tag to arrive here
+          # from Gitea (what 0.3.2 did) would wait forever. The tag this
+          # pipeline minted on Gitea is in fact *deleted* by the next mirror
+          # sync until Codeberg has it — so pushing it here is what makes it
+          # durable on both forges.
+          #
+          # Pushing the ref first and attaching with NO target_commitish is
+          # deliberate: a release POST carrying a target_commitish for a commit
+          # or tag Codeberg hasn't received yet is what produced the
+          # empty-bodied 500s. Attaching to a ref that already exists doesn't
+          # need the API to write one.
+          git tag -f "$TAG" "$SHA"
+          git push -f "https://jlmakiola:${TOKEN}@codeberg.org/jlmakiola/agendula.git" \
+            "refs/tags/$TAG"
+          python3 - "$TAG" "$PRERELEASE" <<'PY' > cb-payload.json
           import json, sys
-          tag, sha, pre, tag_code = sys.argv[1:5]
-          payload = {
+          tag, pre = sys.argv[1:3]
+          print(json.dumps({
               "tag_name": tag,
               "name": tag,
               "body": open("release-notes.md").read(),
               "draft": False,
               # Pre-1.0 releases are flagged as pre-releases (see detect job).
               "prerelease": pre == "true",
-          }
-          # Only create the tag via the release when it isn't mirrored yet.
-          if tag_code != "200":
-              payload["target_commitish"] = sha
-          print(json.dumps(payload))
+          }))
           PY
-          # Upsert (re-run safe).
-          ID=$(curl -s -H "Authorization: token $TOKEN" "$API/releases/tags/$TAG" | jq -r '.id // empty')
-          if [ -n "$ID" ]; then
-            curl -s -o /dev/null -w "release PATCH HTTP %{http_code}\n" -X PATCH \
+          # Create (or update) the release. Codeberg 500s on a POST/GET against a
+          # tag it has only just received — the release request outruns the
+          # indexing of the ref we pushed a moment ago — so a single attempt can
+          # fail even though the very same call succeeds seconds later. Retry
+          # with backoff, and PATCH in place if a release already exists (re-run
+          # safe, so re-running never disturbs a published release). A 5xx body
+          # still exits curl 0, so the loop, not `set -e`, controls the flow.
+          ID=""
+          for attempt in 1 2 3 4 5 6; do
+            EXIST=$(curl -s -H "Authorization: token $TOKEN" "$API/releases/tags/$TAG" | jq -r '.id // empty' 2>/dev/null || true)
+            if [ -n "$EXIST" ]; then
+              curl -s -o /dev/null -w "release PATCH HTTP %{http_code}\n" -X PATCH \
+                -H "Authorization: token $TOKEN" -H "Content-Type: application/json" \
+                -d @cb-payload.json "$API/releases/$EXIST"
+              ID="$EXIST"; break
+            fi
+            CODE=$(curl -s -o cb-response.json -w "%{http_code}" -X POST \
               -H "Authorization: token $TOKEN" -H "Content-Type: application/json" \
-              -d @cb-payload.json "$API/releases/$ID"
-          else
-            curl -s -o cb-response.json -w "release POST HTTP %{http_code}\n" -X POST \
-              -H "Authorization: token $TOKEN" -H "Content-Type: application/json" \
-              -d @cb-payload.json "$API/releases"
+              -d @cb-payload.json "$API/releases")
+            echo "release POST attempt $attempt HTTP $CODE"
             ID=$(jq -r '.id // empty' cb-response.json 2>/dev/null || true)
-          fi
-          if [ -z "$ID" ]; then echo "Could not resolve Codeberg release id." >&2; exit 1; fi
+            [ -n "$ID" ] && break
+            sleep $((attempt * 10))
+          done
+          if [ -z "$ID" ]; then echo "Could not resolve Codeberg release id after retries." >&2; exit 1; fi
 
           # Attach APK + checksum, replacing any prior asset of the same name.
           for A in "$ASSET_APK" "$ASSET_SUM"; do

.gitea/workflows/renovate.yml

@@ -0,0 +1,61 @@
+name: Renovate
+
+on:
+  # Weekly sweep. Mondays 05:00 UTC — this cron owns the cadence; the repo's
+  # renovate.json5 deliberately has no internal schedule (avoids double-gating).
+  schedule:
+    - cron: '0 5 * * 1'
+  # Manual run for an on-demand sweep from the Actions tab.
+  workflow_dispatch:
+
+# Never let two Renovate runs touch the repo at once.
+concurrency:
+  group: renovate
+  cancel-in-progress: false
+
+jobs:
+  renovate:
+    # Gitea only — same guard, and the same reason, as release.yaml's `detect`:
+    # this file is invisible to Codeberg only while .forgejo/ is non-empty, and
+    # a repo-write token must never run on the contributor-facing runner.
+    if: github.repository_owner == 'makiolaj'
+    runs-on: docker
+    # Run the Renovate image *as* the job container and invoke the `renovate`
+    # binary directly. The renovatebot/github-action wrapper is a thin Node
+    # action that shells out to `docker run …` — it needs a Docker CLI + socket
+    # inside the job, which the Gitea runner's plain node container has not, so
+    # it died on "Unable to locate executable file: docker". Running the image
+    # directly drops the docker-in-docker requirement entirely.
+    # Full tag pinned; Renovate's github-actions manager keeps it bumped.
+    container:
+      image: ghcr.io/renovatebot/renovate:43.232.0
+    steps:
+      - name: Run Renovate
+        run: renovate
+        env:
+          # Renovate targets Codeberg (canonical) while still RUNNING on the
+          # Gitea runner. Moving the job to Codeberg would put a repo-write
+          # token on the contributor-facing runner, which is exactly what the
+          # .forgejo/ vs .gitea/ split exists to prevent — so the token stays
+          # where the other secrets live and only the API calls cross over.
+          #
+          # Platform is `forgejo`, not `gitea`: Codeberg runs Forgejo, and the
+          # pinned image ships a distinct forgejo platform module.
+          RENOVATE_PLATFORM: forgejo
+          RENOVATE_ENDPOINT: https://codeberg.org/api/v1
+          # Codeberg bot-account token (Gitea secret). Needs repo read/write +
+          # PR scope on jlmakiola/agendula.
+          RENOVATE_TOKEN: ${{ secrets.RENOVATE_TOKEN }}
+          # Scope to this repo only — no org-wide autodiscovery.
+          RENOVATE_AUTODISCOVER: 'false'
+          RENOVATE_REPOSITORIES: '["jlmakiola/agendula"]'
+          # Commits/PRs authored as the bot, not a real maintainer. This address
+          # must be a verified email on the Codeberg bot account, otherwise the
+          # commits show up unattributed there.
+          RENOVATE_GIT_AUTHOR: 'Renovate Bot <renovate@jeanlucmakiola.de>'
+          # Read-only github.com PAT (no scopes needed). Nearly every dependency
+          # is *released* on GitHub, and without this, changelog/release-note
+          # lookups hit the 60/h anonymous rate limit and PRs arrive with an
+          # empty "Release Notes" section.
+          RENOVATE_GITHUB_COM_TOKEN: ${{ secrets.GITHUB_COM_TOKEN }}
+          LOG_LEVEL: info

.gitignore

@@ -53,5 +53,19 @@ Thumbs.db
 # F-Droid local artifacts (the pipeline generates them in CI)
 /fdroid/
 
+# Release-pipeline scratch files. release.yaml writes these into the workspace
+# while cutting a release; a self-hosted runner reuses that workspace, so they
+# must never end up committed (release-notes.md did, through 0.3.2).
+/release-notes.md
+/payload.json
+/existing.json
+/response.json
+/cb-payload.json
+/cb-response.json
+
 # KSP
 .ksp/
+
+# Local agent notes: machine-specific build setup and on-device rules, not
+# anything the project itself depends on.
+/CLAUDE.md

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "floret-kit"]
 	path = floret-kit
-	url = https://gitea.jeanlucmakiola.de/makiolaj/floret-kit.git
+	url = https://codeberg.org/jlmakiola/floret-kit.git

CHANGELOG.md

@@ -8,22 +8,47 @@ All notable changes to this project are documented here. The format follows
 ## [Unreleased]
 
 ### Added
-- M5 reminders onboarding & polish: a one-time reminder onboarding step after the
-  provider grant explains that Agendula delivers due reminders itself and requests
-  `POST_NOTIFICATIONS` (API 33+). A new **Settings** screen (gear on the lists
-  overview), structured after Calendula as a category hub with sliding sub-screens
-  (`CollapsingScaffold` + grouped category rows + full-screen `OptionPicker`):
-  an About card, **Appearance** (theme, dynamic colour), **Task form** (which
-  optional edit-form fields show by default, default list, the add-a-subtask-row
-  opt-out), and **Reminders** (a master enable switch that re-requests the
-  notification permission, a "when to remind" default offset, and — on Android 12
-  only — an exact-alarm status row that deep-links to system settings).
-- The reminders master switch gates the whole engine: turning it off clears every
-  scheduled alarm and suppresses any that fire.
-- Expressive top-bar actions: a reusable `ShapedActionButton` wraps an action icon
-  in a tonal M3 Expressive `MaterialShapes` container (the settings entry uses the
-  faceted Gem shape, tertiary tones), with a small press scale/rotate flourish.
-  Future top-bar actions pick their own shape from the `ActionShapes` registry.
+- Agendula can now be translated. Pick or request a language on Weblate and
+  translate in the browser — the link sits at the top of the language picker in
+  **Settings → App language**. Partial translations are fine; anything
+  untranslated falls back to English.
+
+### Changed
+- Agendula's home is now **Codeberg** (`jlmakiola/agendula`) — that's where the
+  source, issues, pull requests and releases live. The Source and License links
+  in Settings, the issue-reporting link and the F-Droid metadata all point there
+  now. The self-hosted Gitea instance stays as build infrastructure.
+
+## [0.3.2] - 2026-07-20
+
+### Fixed
+- Releases reach the Codeberg download channel again. 0.3.1 published to
+  F-Droid but never appeared on Codeberg, so if you install from there — or
+  through Obtainium — this is the release that finally carries 0.3.0's
+  launch-crash fix. The app itself is unchanged from 0.3.1.
+
+## [0.3.1] - 2026-07-20
+
+### Fixed
+- Agendula no longer crashes on launch. Every 0.3.0 install was affected: the
+  release build stripped a constructor that the background-work scheduler needs
+  to open its database, and that happens before the app draws anything.
+
+## [0.3.0] - 2026-07-19
+
+### Added
+- Reminders: Agendula now delivers your due reminders itself. A one-time setup
+  step explains this and asks for notification access, and a master switch in
+  Settings turns the whole thing off again.
+- A Settings screen, from the gear on the overview: appearance and theme, which
+  fields the task form shows, your default list, and reminder defaults.
+- The overview leads with Today — a progress ring showing how much of today
+  you've finished — followed by a live preview of what's coming up next.
+- Search across every task, open or completed, from the top bar.
+- A proper app icon.
+
+### Changed
+- A tidier top bar: no app title, with search and settings pinned to the right.
 
 ## [0.2.2] - 2026-07-19
 

CONTRIBUTING.md

@@ -33,10 +33,33 @@ would expose provider details to a ViewModel or the UI, it's in the wrong layer.
 ./gradlew lintDebug                 # Android lint (CI runs this on every PR)
 ```
 
-CI (`.gitea/workflows/ci.yaml`) runs a reproducible-release invariant check,
+CI (`.forgejo/workflows/ci.yaml`, on Codeberg) runs a reproducible-release invariant check,
 then lint → unit tests → debug build on every pull request, so run these locally
 before opening a PR. Keep CI green.
 
+## Translations
+
+**Never edit a `values-*/strings.xml` file in a pull request.** Translations are
+owned by a self-hosted Weblate that writes to this repository directly, and a
+hand-edit is overwritten on the next sync.
+
+→ **[Translate Agendula on Weblate](https://weblate.dev.jeanlucmakiola.de/engage/agendula/)**
+
+Adding a *new* English string to `values/strings.xml` is normal PR work; Weblate
+picks it up and offers it to translators. Partial translations are expected and
+fine — missing keys are informational. Stale and orphaned keys are not, so run
+
+```sh
+python3 scripts/check_translations.py
+```
+
+before pushing. It reports those more clearly than lint's `MissingTranslation`
+does, and it's what the `Translations` check runs on every PR.
+
+A new language also needs one `<locale>` line in
+`app/src/main/res/xml/locales_config.xml` — that file is the single source of
+truth for both the in-app picker and the Android 13+ per-app language setting.
+
 ## Where to put code
 
 | Layer | Lives in | Rule of thumb |

README.md

@@ -3,9 +3,10 @@
 <h1>Agendula</h1>
 
 <p><strong>A modern Material 3 Expressive task app for Android.</strong><br>
-Reads, writes, and reminds — on top of an existing tasks provider, with no own
-sync stack.</p>
+Keeps your tasks on your device, or on top of a tasks provider you already use.
+Open standards, no account required.</p>
 
+<a href="https://codeberg.org/jlmakiola/agendula/actions"><img src="https://codeberg.org/jlmakiola/agendula/actions/workflows/ci.yaml/badge.svg?branch=main" alt="CI"></a>
 <img src="https://img.shields.io/badge/Android-10%2B-3DDC84?logo=android&logoColor=white" alt="Android 10+">
 <img src="https://img.shields.io/badge/Kotlin-Compose-7F52FF?logo=kotlin&logoColor=white" alt="Kotlin + Compose">
 <img src="https://img.shields.io/badge/Material%203-Expressive-4285F4" alt="Material 3 Expressive">
@@ -13,32 +14,66 @@ sync stack.</p>
 
 </div>
 
-Agendula is the task-list sibling to [Calendula](https://gitea.jeanlucmakiola.de/makiolaj/calendula).
-Where Calendula is a pure front-end over Android's `CalendarContract`, Agendula is
-a pure front-end over the **OpenTasks `TaskContract` provider** — the store that
-DAVx5 (and SmoothSync, DecSync, …) syncs your CalDAV `VTODO` tasks into. No own
-database, no reinvented sync.
+Agendula is the task-list sibling to [Calendula](https://codeberg.org/jlmakiola/calendula).
+Where Calendula is a pure front-end over Android's `CalendarContract`, Agendula
+keeps its own store, designed around RFC 5545's `VTODO` — the same tasks DAVx5
+(and SmoothSync, DecSync, …) sync out of your CalDAV server. It can also read and
+write a tasks provider you already have, for anyone already syncing that way.
 
 The name rhymes with its sibling on purpose: **Agendula** is *agenda* — Latin for
 “things to be done” — given Calendula's `-ula` ending. Calendula keeps your days;
 Agendula keeps your to-dos. (A Calendula flower head is botanically a cluster of
 many small *florets* — so the two apps are florets of one bloom.)
 
-> **Status: data layer done, UI in progress.** The full non-visual stack over
-> the `TaskContract` provider — provider resolution, live-updating reads,
-> writes, smart-list filtering, and a self-scheduled reminder engine — is built
-> and unit-tested. The Material 3 Expressive screens are now being built on top,
-> one at a time. See [`docs/ROADMAP.md`](docs/ROADMAP.md) for status,
+## Where your tasks live — your choice
+
+|  | Where | Sync | Needs |
+|---|---|---|---|
+| **On your device** *(default)* | Agendula's own database | none yet — CalDAV sync of our own is planned | nothing. No account, no permissions, no other app |
+| **In a provider you already use** | OpenTasks or tasks.org | whatever syncs it for you — DAVx5 and friends | that app installed, and its read/write permission |
+
+Agendula's own store is an ordinary app database — nothing is published to other
+apps, so there is no authority to clash over and no permission to grant. It
+**coexists with OpenTasks rather than replacing it**: installing one never breaks
+the other, and if you already sync through a provider, that keeps working exactly
+as it did.
+
+Recurring tasks are expanded per RFC 5545, and everything the schema does not
+model is round-tripped verbatim rather than dropped — so passing your tasks
+through Agendula does not quietly lose fields a server sent.
+
+Your tasks are exportable as standard iCalendar `.ics` files at any time, because
+data you can't take with you isn't really yours.
+
+> **Status: backend complete, UI catching up.** Storage, reads and
+> writes, smart-list filtering, a self-scheduled reminder engine, and export are
+> built and unit-tested. The Material 3 Expressive screens are being built on
+> top, one at a time — the storage-mode picker and export screen are not there
+> yet. See [`docs/ROADMAP.md`](docs/ROADMAP.md) for status,
 > [`docs/ARCHITECTURE.md`](docs/ARCHITECTURE.md) for how it's built, and
-> [`docs/PLAN.md`](docs/PLAN.md) for the A-now-B-later design rationale.
+> [`docs/STORAGE-AND-SYNC.md`](docs/STORAGE-AND-SYNC.md) for why storage works
+> the way it does.
 
 ## Sync sources (by design)
 
-Agendula works with anything that writes to the tasks provider — **DAVx5**
-(CalDAV), **SmoothSync**, **CalDAV-Sync**, **DecSync CC**, or any Android sync
-adapter — because it builds on the provider, not on any one sync app. Google
-Tasks / Microsoft To Do are out of scope by design (proprietary; they would mean
-owning a sync stack). Open standards — CalDAV / iCalendar / DecSync — are the lane.
+In external-provider mode Agendula works with anything that writes to that provider —
+**DAVx5** (CalDAV), **SmoothSync**, **CalDAV-Sync**, **DecSync CC**, or any
+Android sync adapter — because it builds on the provider, not on any one sync
+app. Google Tasks / Microsoft To Do are out of scope by design (proprietary; they
+would mean owning a sync stack). Open standards — CalDAV / iCalendar / DecSync —
+are the lane.
+
+## Translations
+
+Agendula ships in English so far, and would like not to. Translations are
+managed on a self-hosted **Weblate**, and partial ones are fine — an
+untranslated string simply falls back to English.
+
+**→ [Help translate Agendula](https://weblate.dev.jeanlucmakiola.de/engage/agendula/)**
+
+No coding needed: register on the Weblate server, pick (or request) a language,
+and translate the strings in your browser. You can also reach this link in the
+app from the top of **Settings → App language**.
 
 ## License
 

app/build.gradle.kts

@@ -29,8 +29,8 @@ android {
         // release itself (versionCode is pinned to MAJOR*10000 + MINOR*100 +
         // PATCH from versionName, e.g. 0.2.0 -> 200). The Gitea release is marked
         // as a pre-release while MAJOR is 0. See docs/RELEASING.md.
-        versionCode = 202
-        versionName = "0.2.2"
+        versionCode = 302
+        versionName = "0.3.2"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }
@@ -111,12 +111,28 @@ android {
         }
     }
 
+    lint {
+        // Community translations are expected to be partial — a missing string
+        // falls back to the English base at runtime — so don't fail the build on
+        // it. Likewise a translated <plurals> may not fill every CLDR quantity
+        // form its locale defines (e.g. Arabic needs "zero"); the missing form
+        // falls back to "other" at runtime, so MissingQuantity is informational
+        // too. Stale/extra keys (ExtraTranslation) stay fatal; scripts/
+        // check_translations.py guards the same invariants with clearer,
+        // translator-facing messages.
+        informational += listOf("MissingTranslation", "MissingQuantity")
+    }
+
     testOptions {
         unitTests {
             all { it.useJUnitPlatform() }
             isReturnDefaultValues = true
         }
     }
+
+    // MigrationTestHelper reads the exported schemas out of the test APK's
+    // assets, so app/schemas/ has to ship with the instrumented tests.
+    sourceSets.getByName("androidTest").assets.srcDir("$projectDir/schemas")
 }
 
 kotlin {
@@ -125,11 +141,27 @@ kotlin {
     }
 }
 
+// Export each Room schema version to app/schemas/ and commit it. That JSON is
+// what MigrationTestHelper reads to build an old database and migrate it, so
+// without it a migration can only be tested by hand.
+ksp {
+    arg("room.schemaLocation", "$projectDir/schemas")
+}
+
 dependencies {
+    // Not a dependency we use directly — lifecycle already drags it in at 1.7.3.
+    // AGP's consistent resolution then pins androidTest to the app classpath, and
+    // room-testing's MigrationTestHelper needs 1.8+ to deserialize the exported
+    // schema; on 1.7.3 it dies with an AbstractMethodError. Raise it in one place.
+    constraints {
+        implementation(libs.kotlinx.serialization.json)
+    }
+
     implementation(libs.androidx.core.ktx)
     implementation(libs.androidx.appcompat)
     implementation(libs.androidx.lifecycle.runtime.ktx)
     implementation(libs.androidx.lifecycle.runtime.compose)
+    implementation(libs.androidx.lifecycle.process)
     implementation(libs.androidx.activity.compose)
 
     implementation(platform(libs.androidx.compose.bom))
@@ -145,7 +177,17 @@ dependencies {
     implementation(libs.androidx.navigation.compose)
     ksp(libs.hilt.compiler)
 
+    // RFC 5545 recurrence expansion, in-process. Pinned at 0.12.2 — 0.16.0
+    // removed RecurrenceSet. rfc5545-datetime comes with it and is part of its
+    // API surface, so it isn't declared separately.
+    implementation(libs.dmfs.lib.recur)
+
+    implementation(libs.androidx.room.runtime)
+    implementation(libs.androidx.room.ktx)
+    ksp(libs.androidx.room.compiler)
+
     implementation(libs.androidx.datastore.preferences)
+    implementation(libs.androidx.documentfile)
 
     implementation(libs.androidx.glance.appwidget)
     implementation(libs.androidx.glance.material3)
@@ -173,6 +215,7 @@ dependencies {
     androidTestImplementation(libs.androidx.espresso.core)
     androidTestImplementation(libs.androidx.test.rules)
     androidTestImplementation(libs.truth)
+    androidTestImplementation(libs.androidx.room.testing)
     androidTestImplementation(platform(libs.androidx.compose.bom))
     androidTestImplementation(libs.androidx.ui.test.junit4)
 }

app/proguard-rules.pro

@@ -2,5 +2,20 @@
 -keep class dagger.hilt.** { *; }
 -keep @dagger.hilt.android.HiltAndroidApp class *
 
+# Room instantiates its generated <Database>_Impl reflectively through a no-arg
+# constructor. R8 under AGP 9 keeps the class but prunes that constructor, since
+# nothing calls it directly — Room then throws InstantiationException, reported
+# as "Failed to create an instance of ...". We pull Room in transitively via
+# Glance -> WorkManager, whose WorkDatabase is built by WorkManagerInitializer
+# at startup, so the app died on launch in every minified build (issue #1).
+-keep class * extends androidx.room.RoomDatabase { <init>(); }
+
+# WorkManager likewise looks its workers up by name and calls this constructor
+# reflectively — same pruning, but it only bites once a worker actually runs
+# (Glance's widget updates), so keep it explicitly rather than wait for it.
+-keep class * extends androidx.work.ListenableWorker {
+    <init>(android.content.Context, androidx.work.WorkerParameters);
+}
+
 # Compose Compiler may keep its own; defaults are fine
 -dontwarn org.jetbrains.annotations.**

app/schemas/de.jeanlucmakiola.agendula.data.tasks.room.TasksDatabase/1.json

@@ -0,0 +1,522 @@
+{
+  "formatVersion": 1,
+  "database": {
+    "version": 1,
+    "identityHash": "c94852274d874fe255ee76e1e46a3003",
+    "entities": [
+      {
+        "tableName": "accounts",
+        "createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `display_name` TEXT NOT NULL, `principal_url` TEXT, `home_set_url` TEXT, `username` TEXT, `last_sync_at` INTEGER, `last_sync_error` TEXT)",
+        "fields": [
+          {
+            "fieldPath": "id",
+            "columnName": "id",
+            "affinity": "INTEGER",
+            "notNull": true
+          },
+          {
+            "fieldPath": "displayName",
+            "columnName": "display_name",
+            "affinity": "TEXT",
+            "notNull": true
+          },
+          {
+            "fieldPath": "principalUrl",
+            "columnName": "principal_url",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "homeSetUrl",
+            "columnName": "home_set_url",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "username",
+            "columnName": "username",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "lastSyncAt",
+            "columnName": "last_sync_at",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "lastSyncError",
+            "columnName": "last_sync_error",
+            "affinity": "TEXT"
+          }
+        ],
+        "primaryKey": {
+          "autoGenerate": true,
+          "columnNames": [
+            "id"
+          ]
+        }
+      },
+      {
+        "tableName": "task_lists",
+        "createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `name` TEXT NOT NULL, `color` INTEGER NOT NULL, `account_id` INTEGER, `is_visible` INTEGER NOT NULL DEFAULT 1, `is_synced` INTEGER NOT NULL DEFAULT 1, `owner` TEXT, `is_read_only` INTEGER NOT NULL DEFAULT 0, `sort_order` INTEGER NOT NULL DEFAULT 0, `href` TEXT, `ctag` TEXT, `sync_token` TEXT, `is_dirty` INTEGER NOT NULL DEFAULT 0, FOREIGN KEY(`account_id`) REFERENCES `accounts`(`id`) ON UPDATE NO ACTION ON DELETE SET NULL )",
+        "fields": [
+          {
+            "fieldPath": "id",
+            "columnName": "id",
+            "affinity": "INTEGER",
+            "notNull": true
+          },
+          {
+            "fieldPath": "name",
+            "columnName": "name",
+            "affinity": "TEXT",
+            "notNull": true
+          },
+          {
+            "fieldPath": "color",
+            "columnName": "color",
+            "affinity": "INTEGER",
+            "notNull": true
+          },
+          {
+            "fieldPath": "accountId",
+            "columnName": "account_id",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "isVisible",
+            "columnName": "is_visible",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "1"
+          },
+          {
+            "fieldPath": "isSynced",
+            "columnName": "is_synced",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "1"
+          },
+          {
+            "fieldPath": "owner",
+            "columnName": "owner",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "isReadOnly",
+            "columnName": "is_read_only",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "0"
+          },
+          {
+            "fieldPath": "sortOrder",
+            "columnName": "sort_order",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "0"
+          },
+          {
+            "fieldPath": "href",
+            "columnName": "href",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "ctag",
+            "columnName": "ctag",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "syncToken",
+            "columnName": "sync_token",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "isDirty",
+            "columnName": "is_dirty",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "0"
+          }
+        ],
+        "primaryKey": {
+          "autoGenerate": true,
+          "columnNames": [
+            "id"
+          ]
+        },
+        "indices": [
+          {
+            "name": "index_task_lists_account_id",
+            "unique": false,
+            "columnNames": [
+              "account_id"
+            ],
+            "orders": [],
+            "createSql": "CREATE INDEX IF NOT EXISTS `index_task_lists_account_id` ON `${TABLE_NAME}` (`account_id`)"
+          }
+        ],
+        "foreignKeys": [
+          {
+            "table": "accounts",
+            "onDelete": "SET NULL",
+            "onUpdate": "NO ACTION",
+            "columns": [
+              "account_id"
+            ],
+            "referencedColumns": [
+              "id"
+            ]
+          }
+        ]
+      },
+      {
+        "tableName": "tasks",
+        "createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `list_id` INTEGER NOT NULL, `uid` TEXT NOT NULL, `href` TEXT, `etag` TEXT, `title` TEXT, `description` TEXT, `location` TEXT, `url` TEXT, `color` INTEGER, `status` INTEGER NOT NULL DEFAULT 0, `percent_complete` INTEGER, `completed_at` INTEGER, `priority` INTEGER NOT NULL DEFAULT 0, `classification` INTEGER, `dtstart` INTEGER, `due` INTEGER, `duration` TEXT, `is_all_day` INTEGER NOT NULL DEFAULT 0, `timezone` TEXT, `rrule` TEXT, `rdate` TEXT, `exdate` TEXT, `recurrence_id` INTEGER, `master_id` INTEGER, `parent_id` INTEGER, `sort_order` INTEGER NOT NULL DEFAULT 0, `created_at` INTEGER, `last_modified` INTEGER, `sequence` INTEGER NOT NULL DEFAULT 0, `is_dirty` INTEGER NOT NULL DEFAULT 0, `is_deleted` INTEGER NOT NULL DEFAULT 0, `unknown_properties` TEXT, FOREIGN KEY(`list_id`) REFERENCES `task_lists`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE , FOREIGN KEY(`master_id`) REFERENCES `tasks`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE , FOREIGN KEY(`parent_id`) REFERENCES `tasks`(`id`) ON UPDATE NO ACTION ON DELETE SET NULL )",
+        "fields": [
+          {
+            "fieldPath": "id",
+            "columnName": "id",
+            "affinity": "INTEGER",
+            "notNull": true
+          },
+          {
+            "fieldPath": "listId",
+            "columnName": "list_id",
+            "affinity": "INTEGER",
+            "notNull": true
+          },
+          {
+            "fieldPath": "uid",
+            "columnName": "uid",
+            "affinity": "TEXT",
+            "notNull": true
+          },
+          {
+            "fieldPath": "href",
+            "columnName": "href",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "etag",
+            "columnName": "etag",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "title",
+            "columnName": "title",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "description",
+            "columnName": "description",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "location",
+            "columnName": "location",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "url",
+            "columnName": "url",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "color",
+            "columnName": "color",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "status",
+            "columnName": "status",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "0"
+          },
+          {
+            "fieldPath": "percentComplete",
+            "columnName": "percent_complete",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "completedAt",
+            "columnName": "completed_at",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "priority",
+            "columnName": "priority",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "0"
+          },
+          {
+            "fieldPath": "classification",
+            "columnName": "classification",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "dtstart",
+            "columnName": "dtstart",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "due",
+            "columnName": "due",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "duration",
+            "columnName": "duration",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "isAllDay",
+            "columnName": "is_all_day",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "0"
+          },
+          {
+            "fieldPath": "timezone",
+            "columnName": "timezone",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "rrule",
+            "columnName": "rrule",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "rdate",
+            "columnName": "rdate",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "exdate",
+            "columnName": "exdate",
+            "affinity": "TEXT"
+          },
+          {
+            "fieldPath": "recurrenceId",
+            "columnName": "recurrence_id",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "masterId",
+            "columnName": "master_id",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "parentId",
+            "columnName": "parent_id",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "sortOrder",
+            "columnName": "sort_order",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "0"
+          },
+          {
+            "fieldPath": "createdAt",
+            "columnName": "created_at",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "lastModified",
+            "columnName": "last_modified",
+            "affinity": "INTEGER"
+          },
+          {
+            "fieldPath": "sequence",
+            "columnName": "sequence",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "0"
+          },
+          {
+            "fieldPath": "isDirty",
+            "columnName": "is_dirty",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "0"
+          },
+          {
+            "fieldPath": "isDeleted",
+            "columnName": "is_deleted",
+            "affinity": "INTEGER",
+            "notNull": true,
+            "defaultValue": "0"
+          },
+          {
+            "fieldPath": "unknownProperties",
+            "columnName": "unknown_properties",
+            "affinity": "TEXT"
+          }
+        ],
+        "primaryKey": {
+          "autoGenerate": true,
+          "columnNames": [
+            "id"
+          ]
+        },
+        "indices": [
+          {
+            "name": "index_tasks_list_id_is_deleted",
+            "unique": false,
+            "columnNames": [
+              "list_id",
+              "is_deleted"
+            ],
+            "orders": [],
+            "createSql": "CREATE INDEX IF NOT EXISTS `index_tasks_list_id_is_deleted` ON `${TABLE_NAME}` (`list_id`, `is_deleted`)"
+          },
+          {
+            "name": "index_tasks_parent_id",
+            "unique": false,
+            "columnNames": [
+              "parent_id"
+            ],
+            "orders": [],
+            "createSql": "CREATE INDEX IF NOT EXISTS `index_tasks_parent_id` ON `${TABLE_NAME}` (`parent_id`)"
+          },
+          {
+            "name": "index_tasks_master_id_recurrence_id",
+            "unique": false,
+            "columnNames": [
+              "master_id",
+              "recurrence_id"
+            ],
+            "orders": [],
+            "createSql": "CREATE INDEX IF NOT EXISTS `index_tasks_master_id_recurrence_id` ON `${TABLE_NAME}` (`master_id`, `recurrence_id`)"
+          },
+          {
+            "name": "index_tasks_is_dirty",
+            "unique": false,
+            "columnNames": [
+              "is_dirty"
+            ],
+            "orders": [],
+            "createSql": "CREATE INDEX IF NOT EXISTS `index_tasks_is_dirty` ON `${TABLE_NAME}` (`is_dirty`)"
+          },
+          {
+            "name": "index_tasks_list_id_uid_recurrence_id",
+            "unique": true,
+            "columnNames": [
+              "list_id",
+              "uid",
+              "recurrence_id"
+            ],
+            "orders": [],
+            "createSql": "CREATE UNIQUE INDEX IF NOT EXISTS `index_tasks_list_id_uid_recurrence_id` ON `${TABLE_NAME}` (`list_id`, `uid`, `recurrence_id`)"
+          }
+        ],
+        "foreignKeys": [
+          {
+            "table": "task_lists",
+            "onDelete": "CASCADE",
+            "onUpdate": "NO ACTION",
+            "columns": [
+              "list_id"
+            ],
+            "referencedColumns": [
+              "id"
+            ]
+          },
+          {
+            "table": "tasks",
+            "onDelete": "CASCADE",
+            "onUpdate": "NO ACTION",
+            "columns": [
+              "master_id"
+            ],
+            "referencedColumns": [
+              "id"
+            ]
+          },
+          {
+            "table": "tasks",
+            "onDelete": "SET NULL",
+            "onUpdate": "NO ACTION",
+            "columns": [
+              "parent_id"
+            ],
+            "referencedColumns": [
+              "id"
+            ]
+          }
+        ]
+      },
+      {
+        "tableName": "task_alarms",
+        "createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `task_id` INTEGER NOT NULL, `minutes_before` INTEGER NOT NULL, `reference` TEXT NOT NULL DEFAULT 'DUE', `message` TEXT, FOREIGN KEY(`task_id`) REFERENCES `tasks`(`id`) ON UPDATE NO ACTION ON DELETE CASCADE )",
+        "fields": [
+          {
+            "fieldPath": "id",
+            "columnName": "id",
+            "affinity": "INTEGER",
+            "notNull": true
+          },
+          {
+            "fieldPath": "taskId",
+            "columnName": "task_id",
+            "affinity": "INTEGER",
+            "notNull": true
+          },
+          {
+            "fieldPath": "minutesBefore",
+            "columnName": "minutes_before",
+            "affinity": "INTEGER",
+            "notNull": true
+          },
+          {
+            "fieldPath": "reference",
+            "columnName": "reference",
+            "affinity": "TEXT",
+            "notNull": true,
+            "defaultValue": "'DUE'"
+          },
+          {
+            "fieldPath": "message",
+            "columnName": "message",
+            "affinity": "TEXT"
+          }
+        ],
+        "primaryKey": {
+          "autoGenerate": true,
+          "columnNames": [
+            "id"
+          ]
+        },
+        "indices": [
+          {
+            "name": "index_task_alarms_task_id",
+            "unique": false,
+            "columnNames": [
+              "task_id"
+            ],
+            "orders": [],
+            "createSql": "CREATE INDEX IF NOT EXISTS `index_task_alarms_task_id` ON `${TABLE_NAME}` (`task_id`)"
+          }
+        ],
+        "foreignKeys": [
+          {
+            "table": "tasks",
+            "onDelete": "CASCADE",
+            "onUpdate": "NO ACTION",
+            "columns": [
+              "task_id"
+            ],
+            "referencedColumns": [
+              "id"
+            ]
+          }
+        ]
+      }
+    ],
+    "setupQueries": [
+      "CREATE TABLE IF NOT EXISTS room_master_table (id INTEGER PRIMARY KEY,identity_hash TEXT)",
+      "INSERT OR REPLACE INTO room_master_table (id,identity_hash) VALUES(42, 'c94852274d874fe255ee76e1e46a3003')"
+    ]
+  }
+}

app/src/androidTest/java/de/jeanlucmakiola/agendula/data/tasks/legacy/OneShotImportTest.kt

@@ -0,0 +1,290 @@
+package de.jeanlucmakiola.agendula.data.tasks.legacy
+
+import android.content.Context
+import androidx.datastore.core.DataStore
+import androidx.datastore.preferences.core.PreferenceDataStoreFactory
+import androidx.datastore.preferences.core.Preferences
+import androidx.room.Room
+import androidx.test.core.app.ApplicationProvider
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.platform.app.InstrumentationRegistry
+import com.google.common.truth.Truth.assertThat
+import de.jeanlucmakiola.agendula.data.tasks.room.AlarmReference
+import de.jeanlucmakiola.agendula.data.tasks.room.TaskEntity
+import de.jeanlucmakiola.agendula.data.tasks.room.TasksDatabase
+import de.jeanlucmakiola.agendula.domain.TaskStatus
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.cancel
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.runBlocking
+import org.junit.After
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import org.junit.rules.TemporaryFolder
+import org.junit.runner.RunWith
+import java.io.File
+import java.util.UUID
+import kotlin.time.Instant
+
+/**
+ * The one-shot import, against `assets/tasks-v23.db` — the dmfs v23 fixture
+ * `scripts/make_import_fixture.py` seeds. Instrumented because both halves need
+ * a real SQLite: the source file and Room.
+ */
+@RunWith(AndroidJUnit4::class)
+class OneShotImportTest {
+
+    @get:Rule
+    val temp = TemporaryFolder()
+
+    private val context: Context = ApplicationProvider.getApplicationContext()
+    private lateinit var scope: CoroutineScope
+    private lateinit var prefs: DataStore<Preferences>
+    private lateinit var db: TasksDatabase
+    private lateinit var importer: OneShotImport
+
+    @Before
+    fun setUp() {
+        scope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+        prefs = PreferenceDataStoreFactory.create(scope = scope) {
+            temp.newFile("import-${counter++}.preferences_pb").also(File::delete)
+        }
+        db = Room.inMemoryDatabaseBuilder(context, TasksDatabase::class.java)
+            .allowMainThreadQueries()
+            .build()
+        importer = OneShotImport(context, db, prefs)
+        legacyFile().delete()
+        archiveFile().delete()
+    }
+
+    @After
+    fun tearDown() {
+        db.close()
+        scope.cancel()
+        legacyFile().delete()
+        archiveFile().delete()
+    }
+
+    private fun legacyFile() = context.getDatabasePath(OneShotImport.LEGACY_NAME)
+    private fun archiveFile() = context.getDatabasePath(OneShotImport.ARCHIVE_NAME)
+
+    /** The fixture, copied out of the test APK's assets. */
+    private fun fixture(target: File = temp.newFile("tasks-v23-copy.db")): File {
+        InstrumentationRegistry.getInstrumentation().context.assets.open(FIXTURE).use { source ->
+            target.outputStream().use(source::copyTo)
+        }
+        return target
+    }
+
+    private fun taskRows(): Map<String, TaskEntity> =
+        db.tasks().tasks(null, includeCompleted = true).associate { it.task.title!! to it.task }
+
+    // --- what lands -----------------------------------------------------------
+
+    @Test
+    fun importsEveryLiveTaskAndLeavesTheDeletedOneBehind() {
+        val counts = importer.importFrom(fixture())
+
+        assertThat(counts).isEqualTo(ImportCounts(lists = 3, tasks = 8, alarms = 2))
+        assertThat(taskRows().keys).containsExactly(
+            "Buy milk",
+            "Call the dentist",
+            "Gather receipts",
+            "Renew domain",
+            "Water the plants",
+            "Team offsite",
+            "Task in a hidden list",
+            "Ship the release",
+        )
+    }
+
+    @Test
+    fun importsEveryListAsADeviceOnlyListWithItsFlags() {
+        importer.importFrom(fixture())
+
+        val lists = db.taskLists().lists().associateBy { it.list.name }
+        assertThat(lists.keys).containsExactly("Personal", "Hidden list", "Work")
+        assertThat(lists.values.map { it.list.accountId }).containsExactly(null, null, null)
+        assertThat(lists.getValue("Personal").list.isVisible).isTrue()
+        assertThat(lists.getValue("Hidden list").list.isVisible).isFalse()
+        // The list that sat under a real account: still imported, owner kept.
+        assertThat(lists.getValue("Work").list.owner).isEqualTo("Me")
+        assertThat(lists.getValue("Work").list.color).isEqualTo(0xFF2244AA.toInt())
+    }
+
+    @Test
+    fun carriesTheTaskFieldsAcross() {
+        importer.importFrom(fixture())
+        val tasks = taskRows()
+
+        val milk = tasks.getValue("Buy milk")
+        assertThat(milk.due).isEqualTo(Instant.fromEpochMilliseconds(T0 + DAY))
+        assertThat(milk.status).isEqualTo(TaskStatus.NEEDS_ACTION)
+        assertThat(milk.createdAt).isEqualTo(Instant.fromEpochMilliseconds(T0))
+
+        val dentist = tasks.getValue("Call the dentist")
+        assertThat(dentist.status).isEqualTo(TaskStatus.IN_PROCESS)
+        assertThat(dentist.percentComplete).isEqualTo(40)
+
+        val domain = tasks.getValue("Renew domain")
+        assertThat(domain.status).isEqualTo(TaskStatus.COMPLETED)
+        assertThat(domain.completedAt).isEqualTo(Instant.fromEpochMilliseconds(T0 - DAY))
+
+        val plants = tasks.getValue("Water the plants")
+        assertThat(plants.rrule).isEqualTo("FREQ=WEEKLY;BYDAY=MO,TH")
+        assertThat(plants.timezone).isEqualTo("Europe/Berlin")
+        assertThat(plants.dtstart).isEqualTo(Instant.fromEpochMilliseconds(T0))
+
+        assertThat(tasks.getValue("Team offsite").isAllDay).isTrue()
+    }
+
+    // --- uids -----------------------------------------------------------------
+
+    @Test
+    fun keepsExistingUidsAndMintsOneWhereTheLegacyRowHadNone() {
+        importer.importFrom(fixture())
+        val tasks = taskRows()
+
+        assertThat(tasks.getValue("Buy milk").uid).isEqualTo("a1b2c3d4-0000-4000-8000-000000000001")
+        // The external-account row's uid is what lets it be re-attached later.
+        assertThat(tasks.getValue("Ship the release").uid)
+            .isEqualTo("a1b2c3d4-0000-4000-8000-000000000009")
+
+        val minted = tasks.getValue("Call the dentist").uid
+        assertThat(minted).isNotEmpty()
+        assertThat(UUID.fromString(minted).version()).isEqualTo(4)
+        assertThat(tasks.values.map { it.uid }.toSet()).hasSize(tasks.size)
+    }
+
+    // --- the id remap ---------------------------------------------------------
+
+    @Test
+    fun remapsListIdsOntoTheNewRowIds() {
+        importer.importFrom(fixture())
+
+        val lists = db.taskLists().lists().associateBy { it.list.name }
+        val byList = db.tasks().tasks(null, includeCompleted = true)
+            .groupBy { it.task.listId }
+            .mapValues { (_, rows) -> rows.size }
+
+        assertThat(byList[lists.getValue("Personal").list.id]).isEqualTo(6)
+        assertThat(byList[lists.getValue("Hidden list").list.id]).isEqualTo(1)
+        assertThat(byList[lists.getValue("Work").list.id]).isEqualTo(1)
+        // No task kept a dmfs row id that Room never handed out.
+        assertThat(byList.keys).containsExactlyElementsIn(lists.values.map { it.list.id })
+    }
+
+    @Test
+    fun remapsParentIdsOntoTheNewRowIds() {
+        importer.importFrom(fixture())
+        val tasks = taskRows()
+
+        val parent = tasks.getValue("Buy milk")
+        val child = tasks.getValue("Gather receipts")
+        assertThat(child.parentId).isEqualTo(parent.id)
+        assertThat(db.tasks().subtasks(parent.id).map { it.task.title }).containsExactly("Gather receipts")
+        assertThat(tasks.values.filter { it.parentId != null }).hasSize(1)
+    }
+
+    // --- alarms ---------------------------------------------------------------
+
+    @Test
+    fun importsAlarmsAndSkipsEveryOtherProperty() {
+        importer.importFrom(fixture())
+        val tasks = taskRows()
+
+        assertThat(db.alarms().all()).hasSize(2)
+
+        val milk = db.alarms().forTask(tasks.getValue("Buy milk").id).single()
+        assertThat(milk.minutesBefore).isEqualTo(30)
+        assertThat(milk.reference).isEqualTo(AlarmReference.DUE)
+        assertThat(milk.message).isNull()
+
+        val release = db.alarms().forTask(tasks.getValue("Ship the release").id).single()
+        assertThat(release.minutesBefore).isEqualTo(1440)
+        assertThat(release.reference).isEqualTo(AlarmReference.DUE)
+        assertThat(release.message).isEqualTo("Ship it")
+
+        // The category property on task 1 is not an alarm.
+        assertThat(db.alarms().all().map { it.message }).doesNotContain("Errands")
+    }
+
+    // --- running it -----------------------------------------------------------
+
+    @Test
+    fun runIfNeededImportsArchivesTheSourceAndThenDoesNothing() = runBlocking {
+        fixture(legacyFile())
+
+        val first = importer.runIfNeeded()
+
+        assertThat(first).isEqualTo(ImportResult.Imported(ImportCounts(3, 8, 2)))
+        assertThat(legacyFile().exists()).isFalse()
+        assertThat(archiveFile().exists()).isTrue()
+        assertThat(importer.isDone.first()).isTrue()
+
+        val second = importer.runIfNeeded()
+
+        assertThat(second).isEqualTo(ImportResult.AlreadyDone)
+        assertThat(taskRows()).hasSize(8)
+    }
+
+    @Test
+    fun anInterruptedImportResumesFromTheArchiveWithoutDoubling() = runBlocking {
+        // The process dying between the commit and the flag write is the one gap
+        // the DataStore flag cannot cover on its own. Because the rename happens
+        // first and the import always replaces, the next run finds the archive and
+        // redoes the same work rather than importing a second copy.
+        fixture(legacyFile())
+        importer.runIfNeeded()
+        importer.clearCompletion()
+
+        val resumed = importer.runIfNeeded()
+
+        assertThat(resumed).isEqualTo(ImportResult.Imported(ImportCounts(3, 8, 2)))
+        assertThat(taskRows()).hasSize(8)
+        assertThat(db.taskLists().lists()).hasSize(3)
+        assertThat(db.alarms().all()).hasSize(2)
+    }
+
+    @Test
+    fun runIfNeededMarksItselfDoneWhenThereIsNoLegacyDatabase() = runBlocking {
+        assertThat(importer.runIfNeeded()).isEqualTo(ImportResult.NothingToImport)
+        assertThat(importer.isDone.first()).isTrue()
+        assertThat(taskRows()).isEmpty()
+    }
+
+    @Test
+    fun reimportFromTheArchiveReplacesRatherThanMerges() = runBlocking {
+        fixture(legacyFile())
+        importer.runIfNeeded()
+
+        val again = importer.reimportFromArchive()
+
+        assertThat(again).isEqualTo(ImportResult.Imported(ImportCounts(3, 8, 2)))
+        assertThat(db.taskLists().lists()).hasSize(3)
+        assertThat(taskRows()).hasSize(8)
+        assertThat(db.alarms().all()).hasSize(2)
+        assertThat(archiveFile().exists()).isTrue()
+    }
+
+    @Test
+    fun replacingTwiceFromTheSameFileLeavesOneCopy() {
+        importer.importFrom(fixture())
+        val counts = importer.importFrom(fixture(temp.newFile("second.db")), replaceExisting = true)
+
+        assertThat(counts).isEqualTo(ImportCounts(3, 8, 2))
+        assertThat(taskRows()).hasSize(8)
+        assertThat(db.taskLists().lists()).hasSize(3)
+        assertThat(db.alarms().all()).hasSize(2)
+    }
+
+    private companion object {
+        const val FIXTURE = "tasks-v23.db"
+        const val T0 = 1_768_467_600_000L
+        const val DAY = 86_400_000L
+        var counter = 0
+    }
+}

app/src/androidTest/java/de/jeanlucmakiola/agendula/data/tasks/room/RoomTasksDataSourceTest.kt

@@ -0,0 +1,389 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.Room
+import androidx.test.core.app.ApplicationProvider
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.google.common.truth.Truth.assertThat
+import de.jeanlucmakiola.agendula.data.tasks.TaskQuery
+import de.jeanlucmakiola.agendula.domain.TaskForm
+import de.jeanlucmakiola.agendula.domain.TaskStatus
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import kotlin.time.Clock
+import kotlin.time.Duration.Companion.days
+import kotlin.time.Instant
+
+/**
+ * The seam over Room, exercised through [de.jeanlucmakiola.agendula.data.tasks
+ * .TasksDataSource] rather than the DAOs — recurrence expansion and override
+ * forking only exist at this level.
+ */
+@RunWith(AndroidJUnit4::class)
+class RoomTasksDataSourceTest {
+
+    private lateinit var db: TasksDatabase
+    private lateinit var source: RoomTasksDataSource
+    private var listId = 0L
+
+    /** Truncated to the store's granularity: instants are columns of epoch millis. */
+    private val now get() = Instant.fromEpochMilliseconds(Clock.System.now().toEpochMilliseconds())
+
+    @Before
+    fun setUp() {
+        db = Room.inMemoryDatabaseBuilder(
+            ApplicationProvider.getApplicationContext(),
+            TasksDatabase::class.java,
+        ).allowMainThreadQueries().build()
+        source = RoomTasksDataSource(db)
+        listId = source.createLocalList("Personal", 0xFF112233.toInt())
+    }
+
+    @After
+    fun tearDown() = db.close()
+
+    private fun form(
+        title: String = "task",
+        due: Instant? = null,
+        percentComplete: Int? = null,
+    ) = TaskForm(title = title, listId = listId, due = due, percentComplete = percentComplete)
+
+    /** Turns [taskId] into a weekly series anchored at [anchor]. */
+    private fun makeRecurring(taskId: Long, anchor: Instant, rule: String = "FREQ=WEEKLY") {
+        val entity = db.tasks().entity(taskId)!!
+        db.tasks().update(entity.copy(dtstart = anchor, due = anchor + 1.days, rrule = rule))
+    }
+
+    @Test
+    fun createsAndReadsBackALocalList() {
+        val lists = source.taskLists()
+
+        assertThat(lists).hasSize(1)
+        assertThat(lists.single().name).isEqualTo("Personal")
+        // No account, so the list still has to report something the lists screen
+        // can group under.
+        assertThat(lists.single().isLocal).isTrue()
+        assertThat(lists.single().accountName).isEqualTo("Local")
+    }
+
+    @Test
+    fun renamesAndRecoloursAList() {
+        source.updateList(listId, "  Errands  ", 0xFF445566.toInt())
+
+        val list = source.taskLists().single()
+        assertThat(list.name).isEqualTo("Errands")
+        assertThat(list.color).isEqualTo(0xFF445566.toInt())
+        // Nothing to sync a device-only list to, so the edit leaves it clean.
+        assertThat(db.taskLists().entity(listId)!!.isDirty).isFalse()
+    }
+
+    @Test
+    fun deletingAListTakesItsTasksWithIt() {
+        source.insertTask(form(title = "Buy milk"))
+        source.insertTask(form(title = "Call the bank"))
+        val other = source.createLocalList("Work", 0xFF778899.toInt())
+        val keeper = source.insertTask(TaskForm(title = "Ship it", listId = other))
+
+        source.deleteList(listId)
+
+        assertThat(source.taskLists().map { it.id }).containsExactly(other)
+        assertThat(source.tasks(TaskQuery(includeCompleted = true)).map { it.taskId })
+            .containsExactly(keeper)
+    }
+
+    @Test
+    fun createsAndReadsBackANonRecurringTask() {
+        val due = now + 1.days
+        val id = source.insertTask(form(title = "Buy milk", due = due))
+
+        val task = source.task(id)!!
+
+        assertThat(task.taskId).isEqualTo(id)
+        assertThat(task.title).isEqualTo("Buy milk")
+        assertThat(task.due).isEqualTo(due)
+        assertThat(task.isRecurring).isFalse()
+        // A task that does not recur has no occurrence anchor, so it keys and edits
+        // by task id exactly as it did against the provider.
+        assertThat(task.occurrenceStart).isNull()
+        assertThat(task.occurrenceKey).isEqualTo("$id")
+    }
+
+    @Test
+    fun mintsAUidForEveryTask() {
+        val id = source.insertTask(form())
+
+        assertThat(db.tasks().entity(id)!!.uid).isNotEmpty()
+    }
+
+    @Test
+    fun expandsARecurringSeriesIntoManyOccurrences() {
+        val anchor = now
+        val id = source.insertTask(form(title = "Water the plants"))
+        makeRecurring(id, anchor)
+
+        val occurrences = source.tasks(TaskQuery(listId = listId)).filter { it.taskId == id }
+
+        // The provider materialised exactly one upcoming occurrence; we expand the
+        // whole window, so a weekly series yields well over a hundred.
+        assertThat(occurrences.size).isGreaterThan(100)
+        assertThat(occurrences.map { it.occurrenceStart }).containsNoDuplicates()
+        assertThat(occurrences.map { it.occurrenceKey }).containsNoDuplicates()
+        assertThat(occurrences.all { it.isRecurring }).isTrue()
+        // Each occurrence keeps the series' length rather than the master's dates.
+        val first = occurrences.minBy { it.occurrenceStart!! }
+        assertThat(first.due!! - first.start!!).isEqualTo(1.days)
+    }
+
+    @Test
+    fun exactlyOneOccurrenceIsTheCurrentOne() {
+        val id = source.insertTask(form())
+        makeRecurring(id, now - 30.days)
+
+        val occurrences = source.tasks(TaskQuery(listId = listId)).filter { it.taskId == id }
+
+        assertThat(occurrences.count { it.distanceFromCurrent == 0 }).isEqualTo(1)
+        assertThat(source.task(id)!!.distanceFromCurrent).isEqualTo(0)
+    }
+
+    @Test
+    fun editingOneOccurrenceForksARecurrenceIdOverride() {
+        val anchor = now
+        val id = source.insertTask(form(title = "Water the plants"))
+        makeRecurring(id, anchor)
+        val target = source.tasks(TaskQuery(listId = listId))
+            .filter { it.taskId == id }
+            .first { it.distanceFromCurrent == 1 }
+
+        source.updateInstance(id, target.occurrenceStart!!, form(title = "Water them twice"))
+
+        val override = db.tasks().override(id, target.occurrenceStart)!!
+        // RFC 5545's model: the override shares its master's UID — that is what
+        // makes it an override rather than a separate task. The dmfs provider
+        // detached the occurrence into a new task with its own UID instead.
+        assertThat(override.uid).isEqualTo(db.tasks().entity(id)!!.uid)
+        assertThat(override.masterId).isEqualTo(id)
+        assertThat(override.recurrenceId).isEqualTo(target.occurrenceStart)
+        assertThat(override.rrule).isNull()
+        assertThat(override.title).isEqualTo("Water them twice")
+    }
+
+    @Test
+    fun completingOneOccurrenceLeavesTheRestOfTheSeriesOpen() {
+        val id = source.insertTask(form(title = "Water the plants"))
+        makeRecurring(id, now)
+        val open = { source.tasks(TaskQuery(listId = listId)).filter { it.taskId == id } }
+        val before = open()
+        val target = before.first { it.distanceFromCurrent == 0 }
+
+        source.setCompletedInstance(id, target.occurrenceStart!!, completed = true)
+
+        // Writing the status onto the master would close the series: the master is
+        // the row the task query filters on, so every occurrence would vanish.
+        val after = open()
+        assertThat(after).hasSize(before.size - 1)
+        assertThat(after.map { it.occurrenceStart }).doesNotContain(target.occurrenceStart)
+        assertThat(db.tasks().entity(id)!!.status).isEqualTo(TaskStatus.NEEDS_ACTION)
+
+        val override = db.tasks().override(id, target.occurrenceStart)!!
+        assertThat(override.uid).isEqualTo(db.tasks().entity(id)!!.uid)
+        assertThat(override.status).isEqualTo(TaskStatus.COMPLETED)
+        assertThat(override.rrule).isNull()
+        // The override stands for *that* occurrence, so it carries the
+        // occurrence's resolved times, not the master's anchor.
+        assertThat(override.dtstart).isEqualTo(target.occurrenceStart)
+    }
+
+    @Test
+    fun reopeningACompletedOccurrenceReusesItsOverride() {
+        val id = source.insertTask(form(title = "Water the plants"))
+        makeRecurring(id, now)
+        val target = source.tasks(TaskQuery(listId = listId))
+            .first { it.taskId == id && it.distanceFromCurrent == 0 }
+
+        source.setCompletedInstance(id, target.occurrenceStart!!, completed = true)
+        source.setCompletedInstance(id, target.occurrenceStart, completed = false)
+
+        assertThat(db.tasks().overrides(id)).hasSize(1)
+        assertThat(db.tasks().override(id, target.occurrenceStart)!!.status)
+            .isEqualTo(TaskStatus.NEEDS_ACTION)
+        assertThat(source.tasks(TaskQuery(listId = listId)).map { it.occurrenceStart })
+            .contains(target.occurrenceStart)
+    }
+
+    @Test
+    fun completingANonRecurringTaskThroughTheInstancePathWritesTheRowItself() {
+        val id = source.insertTask(form(title = "Buy milk", due = now + 1.days))
+
+        source.setCompletedInstance(id, now, completed = true)
+
+        assertThat(db.tasks().overrides(id)).isEmpty()
+        assertThat(db.tasks().entity(id)!!.status).isEqualTo(TaskStatus.COMPLETED)
+    }
+
+    @Test
+    fun anOverrideReplacesOnlyItsOwnOccurrence() {
+        val id = source.insertTask(form(title = "Water the plants"))
+        makeRecurring(id, now)
+        // The list holds this series alone, so no filter is needed — and none can
+        // be written on taskId, since the override reports its own row id.
+        val before = source.tasks(TaskQuery(listId = listId))
+        val target = before.first { it.distanceFromCurrent == 1 }
+
+        source.updateInstance(id, target.occurrenceStart!!, form(title = "Water them twice"))
+
+        val after = source.tasks(TaskQuery(listId = listId))
+        assertThat(after).hasSize(before.size)
+        val edited = after.single { it.title == "Water them twice" }
+        assertThat(edited.occurrenceStart).isEqualTo(target.occurrenceStart)
+        assertThat(after.filter { it.occurrenceStart == target.occurrenceStart }).hasSize(1)
+    }
+
+    /**
+     * An edited occurrence addresses its own row, not the master's. That is what
+     * sends the *next* edit down `updateTask` rather than forking a second time:
+     * an override carries no rule, so it reads back as non-recurring.
+     */
+    @Test
+    fun anEditedOccurrenceReportsTheOverridesOwnId() {
+        val id = source.insertTask(form(title = "Water the plants"))
+        makeRecurring(id, now)
+        val target = source.tasks(TaskQuery(listId = listId)).first { it.distanceFromCurrent == 1 }
+
+        source.updateInstance(id, target.occurrenceStart!!, form(title = "Water them twice"))
+
+        val edited = source.tasks(TaskQuery(listId = listId)).single { it.title == "Water them twice" }
+        val overrideId = db.tasks().override(id, target.occurrenceStart)!!.id
+        assertThat(edited.taskId).isEqualTo(overrideId)
+        assertThat(edited.taskId).isNotEqualTo(id)
+        assertThat(source.task(overrideId)!!.isRecurring).isFalse()
+    }
+
+    @Test
+    fun editingASeriesDoesNotReAnchorItWhenOneOccurrenceIsEdited() {
+        val anchor = now
+        val id = source.insertTask(form())
+        makeRecurring(id, anchor)
+        val target = source.tasks(TaskQuery(listId = listId))
+            .filter { it.taskId == id }
+            .first { it.distanceFromCurrent == 2 }
+
+        source.updateInstance(id, target.occurrenceStart!!, form(due = now + 99.days))
+
+        assertThat(db.tasks().entity(id)!!.dtstart).isEqualTo(anchor)
+    }
+
+    @Test
+    fun updatingANonRecurringTaskWritesThroughToItsRow() {
+        val id = source.insertTask(form(title = "old"))
+
+        source.updateTask(id, form(title = "new"))
+
+        assertThat(source.task(id)!!.title).isEqualTo("new")
+    }
+
+    @Test
+    fun completionTogglesTheWholeTriple() {
+        val id = source.insertTask(form())
+
+        source.setCompleted(id, completed = true)
+        val done = db.tasks().entity(id)!!
+        assertThat(done.status).isEqualTo(TaskStatus.COMPLETED)
+        assertThat(done.percentComplete).isEqualTo(100)
+        assertThat(done.completedAt).isNotNull()
+
+        source.setCompleted(id, completed = false)
+        assertThat(db.tasks().entity(id)!!.completedAt).isNull()
+    }
+
+    @Test
+    fun completedTasksAreExcludedUnlessAskedFor() {
+        val id = source.insertTask(form())
+        source.setCompleted(id, completed = true)
+
+        assertThat(source.tasks(TaskQuery(listId = listId, includeCompleted = false))).isEmpty()
+        assertThat(source.tasks(TaskQuery(listId = listId, includeCompleted = true))).hasSize(1)
+    }
+
+    @Test
+    fun alarmsRoundTripAndReplaceRatherThanAccumulate() {
+        val id = source.insertTask(form(due = now + 1.days))
+
+        source.setAlarm(id, 30)
+        assertThat(source.alarms()[id]).isEqualTo(30)
+
+        source.setAlarm(id, 60)
+        assertThat(db.alarms().forTask(id)).hasSize(1)
+        assertThat(source.alarms()[id]).isEqualTo(60)
+
+        source.setAlarm(id, null)
+        assertThat(source.alarms()).doesNotContainKey(id)
+    }
+
+    @Test
+    fun forkingAnOccurrenceCarriesTheReminderOntoIt() {
+        val id = source.insertTask(form(due = now + 1.days))
+        makeRecurring(id, now)
+        source.setAlarm(id, 30)
+        val target = source.tasks(TaskQuery(listId = listId))
+            .filter { it.taskId == id }
+            .first { it.distanceFromCurrent == 1 }
+
+        source.updateInstance(id, target.occurrenceStart!!, form())
+
+        val override = db.tasks().override(id, target.occurrenceStart)!!
+        assertThat(db.alarms().forTask(override.id).single().minutesBefore).isEqualTo(30)
+    }
+
+    @Test
+    fun deletingATaskInALocalListRemovesItOutright() {
+        val id = source.insertTask(form())
+
+        source.deleteTask(id)
+
+        // No account knows about it, so there is nothing to tombstone for.
+        assertThat(db.tasks().entity(id)).isNull()
+    }
+
+    @Test
+    fun deletingASeriesTakesItsOverridesWithIt() {
+        val id = source.insertTask(form())
+        makeRecurring(id, now)
+        val target = source.tasks(TaskQuery(listId = listId))
+            .filter { it.taskId == id }
+            .first { it.distanceFromCurrent == 1 }
+        source.updateInstance(id, target.occurrenceStart!!, form(title = "moved"))
+
+        source.deleteTask(id)
+
+        assertThat(db.tasks().allOverrides(listId)).isEmpty()
+    }
+
+    @Test
+    fun subtasksReadBackUnderTheirParent() {
+        val parent = source.insertTask(form(title = "Prepare invoice"))
+        val child = source.insertTask(form(title = "Gather receipts").copy(parentId = parent))
+
+        assertThat(source.subtasks(parent).map { it.taskId }).containsExactly(child)
+    }
+
+    @Test
+    fun exportReadsMastersNotOccurrences() {
+        val id = source.insertTask(form(title = "Water the plants"))
+        makeRecurring(id, now)
+
+        val exported = source.exportTasks(listId)
+
+        // One row carrying the rule, not one row per occurrence with the rule lost.
+        assertThat(exported).hasSize(1)
+        assertThat(exported.single().rrule).isEqualTo("FREQ=WEEKLY")
+        assertThat(exported.single().uid).isNotEmpty()
+    }
+
+    @Test
+    fun insertingIntoAMissingListFails() {
+        val thrown = runCatching { source.insertTask(form().copy(listId = 9_999)) }.exceptionOrNull()
+
+        assertThat(thrown).isNotNull()
+    }
+}

app/src/androidTest/java/de/jeanlucmakiola/agendula/data/tasks/room/TasksDatabaseMigrationTest.kt

@@ -0,0 +1,68 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.testing.MigrationTestHelper
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.platform.app.InstrumentationRegistry
+import com.google.common.truth.Truth.assertThat
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+
+/**
+ * The migration harness, proven against the committed schema in `app/schemas/`.
+ *
+ * There is one schema version today, so all there is to assert is that the helper
+ * can build v1 from the exported JSON, seed it, and validate it back — i.e. the
+ * export, the assets wiring and the identity hash all line up. That is the point:
+ * the first real migration only has to add its own case.
+ *
+ * **Adding a v1 → v2 case.** When sync adds columns, bump [TasksDatabase]'s
+ * `version`, let KSP export `2.json`, declare the `Migration(1, 2)` next to the
+ * database, and add a test here shaped like this:
+ *
+ * ```
+ * helper.createDatabase(TEST_DB, 1).use { db ->
+ *     db.execSQL("INSERT INTO task_lists (name, color) VALUES ('Groceries', 0)")
+ * }
+ * helper.runMigrationsAndValidate(TEST_DB, 2, true, MIGRATION_1_2).use { db ->
+ *     // read the seeded rows back — validation proves the shape, not the data
+ * }
+ * ```
+ */
+@RunWith(AndroidJUnit4::class)
+class TasksDatabaseMigrationTest {
+
+    @get:Rule
+    val helper = MigrationTestHelper(
+        InstrumentationRegistry.getInstrumentation(),
+        TasksDatabase::class.java,
+    )
+
+    @Test
+    fun buildsV1FromTheExportedSchema() {
+        helper.createDatabase(TEST_DB, 1).use { db ->
+            db.execSQL("INSERT INTO task_lists (id, name, color) VALUES (1, 'Groceries', 0)")
+            db.execSQL("INSERT INTO tasks (id, list_id, uid, title) VALUES (1, 1, 'uid-1', 'Buy milk')")
+
+            db.query("SELECT title FROM tasks").use { cursor ->
+                assertThat(cursor.moveToFirst()).isTrue()
+                assertThat(cursor.getString(0)).isEqualTo("Buy milk")
+            }
+        }
+    }
+
+    @Test
+    fun validatesV1AgainstTheExportedSchema() {
+        helper.createDatabase(TEST_DB, 1).close()
+
+        // No migrations to run: v1 is opened and checked against 1.json, which is
+        // what proves the harness rather than the schema.
+        helper.runMigrationsAndValidate(TEST_DB, 1, true).use { db ->
+            assertThat(db.version).isEqualTo(1)
+        }
+    }
+
+    private companion object {
+        const val TEST_DB = "migration-test.db"
+    }
+}

app/src/androidTest/java/de/jeanlucmakiola/agendula/data/tasks/room/TasksDatabasePerformanceTest.kt

@@ -0,0 +1,107 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import android.content.Context
+import androidx.room.Room
+import androidx.test.core.app.ApplicationProvider
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.google.common.truth.Truth.assertThat
+import de.jeanlucmakiola.agendula.data.tasks.TaskQuery
+import de.jeanlucmakiola.agendula.domain.TaskForm
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import java.io.File
+import kotlin.time.Clock
+import kotlin.time.Duration.Companion.days
+import kotlin.time.measureTime
+import kotlin.time.measureTimedValue
+
+/**
+ * The plan's shape at scale: 5,000 tasks with 20 recurring series, read the way a
+ * smart list reads them — one `tasks(TaskQuery(includeCompleted = true))`, which
+ * includes expanding every series in memory.
+ *
+ * The assertion is a deliberately loose ceiling, so it catches a real regression
+ * rather than CI jitter; the printed numbers are what the check is actually for.
+ */
+@RunWith(AndroidJUnit4::class)
+class TasksDatabasePerformanceTest {
+
+    private val context: Context = ApplicationProvider.getApplicationContext()
+
+    private lateinit var db: TasksDatabase
+    private lateinit var source: RoomTasksDataSource
+    private var listId = 0L
+
+    @Before
+    fun setUp() {
+        delete()
+        db = Room.databaseBuilder(context, TasksDatabase::class.java, DB)
+            .allowMainThreadQueries()
+            .build()
+        source = RoomTasksDataSource(db)
+        listId = source.createLocalList("Everything", 0xFF112233.toInt())
+    }
+
+    @After
+    fun tearDown() {
+        db.close()
+        delete()
+    }
+
+    @Test
+    fun readsFiveThousandTasksWithTwentySeriesInsideTheBudget() {
+        val seeded = measureTime { seed() }
+
+        // Discard the first read: it pays for statement compilation and page cache
+        // warming, which a running app has already paid.
+        source.tasks(TaskQuery(includeCompleted = true))
+        val (tasks, elapsed) = measureTimedValue {
+            source.tasks(TaskQuery(includeCompleted = true))
+        }
+
+        println(
+            "[perf] $TASK_COUNT tasks / $SERIES_COUNT series -> ${tasks.size} occurrences " +
+                "in $elapsed (seed $seeded)",
+        )
+        // Expansion is bounded twice over: the read window is 1 year back and 2
+        // forward, and each series stops at ExpansionWindow.maxOccurrences (500),
+        // so the occurrence count cannot grow with the age of the series.
+        assertThat(tasks.size).isAtLeast(TASK_COUNT)
+        assertThat(elapsed.inWholeMilliseconds).isLessThan(CEILING_MILLIS)
+    }
+
+    private fun seed() {
+        val anchor = Clock.System.now() - 30.days
+        val ids = ArrayList<Long>(TASK_COUNT)
+        db.runInTransaction {
+            repeat(TASK_COUNT) { index ->
+                ids += source.insertTask(
+                    TaskForm(title = "Task $index", listId = listId, due = anchor + index.days),
+                )
+            }
+        }
+        db.runInTransaction {
+            ids.take(SERIES_COUNT).forEach { id ->
+                val entity = db.tasks().entity(id)!!
+                db.tasks().update(
+                    entity.copy(dtstart = anchor, due = anchor + 1.days, rrule = "FREQ=DAILY"),
+                )
+            }
+        }
+    }
+
+    private fun delete() {
+        val base = context.getDatabasePath(DB)
+        base.delete()
+        listOf("-wal", "-shm").forEach { File(base.path + it).delete() }
+    }
+
+    private companion object {
+        const val DB = "performance-test.db"
+        const val TASK_COUNT = 5_000
+        const val SERIES_COUNT = 20
+        const val CEILING_MILLIS = 8_000L
+    }
+}

app/src/androidTest/java/de/jeanlucmakiola/agendula/data/tasks/room/TasksDatabaseRestoreTest.kt

@@ -0,0 +1,155 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import android.content.Context
+import androidx.room.Room
+import androidx.test.core.app.ApplicationProvider
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.google.common.truth.Truth.assertThat
+import de.jeanlucmakiola.agendula.data.tasks.TaskQuery
+import de.jeanlucmakiola.agendula.domain.TaskForm
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import java.io.File
+
+/**
+ * The Auto Backup restore path, on disk.
+ *
+ * Auto Backup copies database files without checkpointing, and Room runs in WAL
+ * mode — so `.db` alone can be a *stale* copy of a database whose recent writes
+ * are still in the `-wal` sidecar. `res/xml/backup_rules.xml` carries all three
+ * files and [DatabaseCheckpoint] truncates the log on `ON_STOP`; this asserts
+ * that both of those actually do what they claim, and that neither alone is an
+ * assumption.
+ *
+ * A file copy of a live database stands in for the backup transport — the
+ * transport is what Auto Backup does to these files, and it is not what is under
+ * test here.
+ */
+@RunWith(AndroidJUnit4::class)
+class TasksDatabaseRestoreTest {
+
+    private val context: Context = ApplicationProvider.getApplicationContext()
+
+    private lateinit var db: TasksDatabase
+    private lateinit var source: RoomTasksDataSource
+    private var listId = 0L
+    private var restored: TasksDatabase? = null
+
+    @Before
+    fun setUp() {
+        delete(LIVE)
+        delete(BACKUP)
+        db = open(LIVE)
+        source = RoomTasksDataSource(db)
+        listId = source.createLocalList("Personal", 0xFF112233.toInt())
+    }
+
+    @After
+    fun tearDown() {
+        restored?.close()
+        db.close()
+        delete(LIVE)
+        delete(BACKUP)
+    }
+
+    @Test
+    fun roomRunsInWalMode() {
+        // Everything below is only interesting because of this.
+        assertThat(journalMode()).isEqualTo("wal")
+    }
+
+    @Test
+    fun aBackupOfTheDbFileAloneLosesWhateverIsStillInTheWal() {
+        write("checkpointed")
+        checkpoint()
+        write("only in the wal")
+
+        backUp(withSidecars = false)
+
+        assertThat(restore()).containsExactly("checkpointed")
+    }
+
+    @Test
+    fun aBackupThatCarriesTheSidecarsKeepsTheLastWrite() {
+        write("checkpointed")
+        checkpoint()
+        write("only in the wal")
+
+        backUp(withSidecars = true)
+
+        assertThat(restore()).containsExactly("checkpointed", "only in the wal")
+    }
+
+    @Test
+    fun checkpointingFirstMakesTheDbFileAloneEnough() {
+        write("checkpointed")
+        checkpoint()
+        write("last write")
+
+        // What DatabaseCheckpoint runs on ON_STOP — the fallback for a restore
+        // that arrives without the sidecars.
+        checkpoint()
+        backUp(withSidecars = false)
+
+        assertThat(restore()).containsExactly("checkpointed", "last write")
+    }
+
+    // --- the moving parts -----------------------------------------------------
+
+    private fun open(name: String): TasksDatabase =
+        Room.databaseBuilder(context, TasksDatabase::class.java, name)
+            .allowMainThreadQueries()
+            .build()
+
+    private fun write(title: String) {
+        source.insertTask(TaskForm(title = title, listId = listId))
+    }
+
+    private fun journalMode(): String =
+        db.openHelper.writableDatabase.query("PRAGMA journal_mode").use { cursor ->
+            cursor.moveToFirst()
+            cursor.getString(0).lowercase()
+        }
+
+    /** [DatabaseCheckpoint]'s pragma, asserting it was not blocked by a reader. */
+    private fun checkpoint() {
+        db.openHelper.writableDatabase.query("PRAGMA wal_checkpoint(TRUNCATE)").use { cursor ->
+            cursor.moveToFirst()
+            assertThat(cursor.getInt(0)).isEqualTo(0)
+        }
+    }
+
+    /** Copies the live database the way Auto Backup would: no checkpoint, files as they lie. */
+    private fun backUp(withSidecars: Boolean) {
+        delete(BACKUP)
+        val live = context.getDatabasePath(LIVE)
+        val backup = context.getDatabasePath(BACKUP)
+        live.copyTo(backup, overwrite = true)
+        if (!withSidecars) return
+        SIDECARS.forEach { suffix ->
+            val from = File(live.path + suffix)
+            if (from.exists()) from.copyTo(File(backup.path + suffix), overwrite = true)
+        }
+    }
+
+    /** Opens the copy as a fresh install would and reports the task titles that survived. */
+    private fun restore(): List<String> {
+        restored?.close()
+        val database = open(BACKUP).also { restored = it }
+        return RoomTasksDataSource(database).tasks(TaskQuery(includeCompleted = true)).map { it.title }
+    }
+
+    private fun delete(name: String) {
+        val base = context.getDatabasePath(name)
+        base.delete()
+        SIDECARS.forEach { File(base.path + it).delete() }
+    }
+
+    private companion object {
+        const val LIVE = "restore-live.db"
+        const val BACKUP = "restore-backup.db"
+        val SIDECARS = listOf("-wal", "-shm")
+    }
+}

app/src/androidTest/java/de/jeanlucmakiola/agendula/data/tasks/room/TasksDatabaseTest.kt

@@ -0,0 +1,274 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.Room
+import androidx.test.core.app.ApplicationProvider
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.google.common.truth.Truth.assertThat
+import de.jeanlucmakiola.agendula.domain.TaskStatus
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import kotlin.time.Instant
+
+/**
+ * The schema, exercised through the DAOs. Instrumented rather than JVM because
+ * the app's unit tests are plain JUnit 5 with no Robolectric, and Room needs a
+ * real SQLite.
+ */
+@RunWith(AndroidJUnit4::class)
+class TasksDatabaseTest {
+
+    private lateinit var db: TasksDatabase
+    private lateinit var lists: TaskListDao
+    private lateinit var tasks: TaskDao
+    private lateinit var alarms: TaskAlarmDao
+    private lateinit var accounts: AccountDao
+
+    @Before
+    fun setUp() {
+        db = Room.inMemoryDatabaseBuilder(
+            ApplicationProvider.getApplicationContext(),
+            TasksDatabase::class.java,
+        ).allowMainThreadQueries().build()
+        lists = db.taskLists()
+        tasks = db.tasks()
+        alarms = db.alarms()
+        accounts = db.accounts()
+    }
+
+    @After
+    fun tearDown() = db.close()
+
+    private fun newList(name: String = "Groceries", accountId: Long? = null): Long =
+        lists.insert(TaskListEntity(name = name, color = 0xFF00FF00.toInt(), accountId = accountId))
+
+    private fun newTask(
+        listId: Long,
+        uid: String = "uid-${counter++}",
+        title: String? = "Buy milk",
+        status: TaskStatus = TaskStatus.NEEDS_ACTION,
+        parentId: Long? = null,
+        masterId: Long? = null,
+        recurrenceId: Instant? = null,
+    ): Long = tasks.insert(
+        TaskEntity(
+            listId = listId,
+            uid = uid,
+            title = title,
+            status = status,
+            parentId = parentId,
+            masterId = masterId,
+            recurrenceId = recurrenceId,
+        ),
+    )
+
+    @Test
+    fun writesAndReadsAListWithItsTasks() {
+        val accountId = accounts.insert(AccountEntity(displayName = "Fastmail"))
+        val listId = newList(accountId = accountId)
+        val due = Instant.fromEpochMilliseconds(1_700_000_000_000)
+        val taskId = tasks.insert(
+            TaskEntity(
+                listId = listId,
+                uid = "uid-1",
+                title = "Buy milk",
+                description = "2%",
+                due = due,
+                priority = 3,
+                status = TaskStatus.IN_PROCESS,
+                percentComplete = 40,
+            ),
+        )
+
+        val list = lists.lists().single()
+        assertThat(list.list.id).isEqualTo(listId)
+        assertThat(list.list.name).isEqualTo("Groceries")
+        assertThat(list.accountDisplayName).isEqualTo("Fastmail")
+
+        val row = tasks.task(taskId)!!
+        assertThat(row.task.title).isEqualTo("Buy milk")
+        assertThat(row.task.due).isEqualTo(due)
+        // Stored raw: an off-bucket PRIORITY must come back as it went in.
+        assertThat(row.task.priority).isEqualTo(3)
+        assertThat(row.task.status).isEqualTo(TaskStatus.IN_PROCESS)
+        assertThat(row.task.percentComplete).isEqualTo(40)
+        assertThat(row.listName).isEqualTo("Groceries")
+        assertThat(row.accountDisplayName).isEqualTo("Fastmail")
+    }
+
+    @Test
+    fun readsTasksOfOneListAndHidesClosedOnesUnlessAsked() {
+        val a = newList("A")
+        val b = newList("B")
+        newTask(a, title = "open")
+        newTask(a, title = "done", status = TaskStatus.COMPLETED)
+        newTask(a, title = "cancelled", status = TaskStatus.CANCELLED)
+        newTask(b, title = "elsewhere")
+
+        assertThat(tasks.tasks(a, includeCompleted = false).map { it.task.title })
+            .containsExactly("open")
+        assertThat(tasks.tasks(a, includeCompleted = true)).hasSize(3)
+        assertThat(tasks.tasks(null, includeCompleted = true)).hasSize(4)
+    }
+
+    @Test
+    fun readsSubtasksByParent() {
+        val listId = newList()
+        val parent = newTask(listId, title = "parent")
+        newTask(listId, title = "child", parentId = parent)
+
+        assertThat(tasks.subtasks(parent).map { it.task.title }).containsExactly("child")
+    }
+
+    @Test
+    fun hidesTombstonesFromReadsAndExports() {
+        val listId = newList()
+        val taskId = newTask(listId)
+        tasks.markDeleted(taskId, Instant.fromEpochMilliseconds(1))
+
+        assertThat(tasks.tasks(listId, includeCompleted = true)).isEmpty()
+        assertThat(tasks.task(taskId)).isNull()
+        assertThat(tasks.exportTasks(listId)).isEmpty()
+        assertThat(tasks.entity(taskId)).isNotNull()
+    }
+
+    @Test
+    fun keepsOverridesOutOfTheMasterReads() {
+        val listId = newList()
+        val master = newTask(listId, uid = "series")
+        val override = newTask(
+            listId,
+            uid = "series",
+            masterId = master,
+            recurrenceId = Instant.fromEpochMilliseconds(5_000),
+        )
+
+        assertThat(tasks.tasks(listId, includeCompleted = true).map { it.task.id })
+            .containsExactly(master)
+        assertThat(tasks.overrides(master).map { it.id }).containsExactly(override)
+        assertThat(tasks.allOverrides(listId).map { it.id }).containsExactly(override)
+        assertThat(tasks.override(master, Instant.fromEpochMilliseconds(5_000))?.id)
+            .isEqualTo(override)
+        assertThat(tasks.exportTasks(listId).map { it.id }).containsExactly(master)
+    }
+
+    // --- cascades -------------------------------------------------------------
+
+    @Test
+    fun deletingAListDeletesItsTasks() {
+        val listId = newList()
+        val taskId = newTask(listId)
+
+        lists.delete(listId)
+
+        assertThat(tasks.entity(taskId)).isNull()
+    }
+
+    @Test
+    fun deletingASeriesDeletesItsOverrides() {
+        val listId = newList()
+        val master = newTask(listId, uid = "series")
+        val override = newTask(
+            listId,
+            uid = "series",
+            masterId = master,
+            recurrenceId = Instant.fromEpochMilliseconds(5_000),
+        )
+
+        tasks.delete(master)
+
+        assertThat(tasks.entity(override)).isNull()
+    }
+
+    @Test
+    fun deletingAParentPromotesItsSubtasks() {
+        val listId = newList()
+        val parent = newTask(listId, title = "parent")
+        val child = newTask(listId, title = "child", parentId = parent)
+
+        tasks.delete(parent)
+
+        val promoted = tasks.entity(child)
+        assertThat(promoted).isNotNull()
+        assertThat(promoted!!.parentId).isNull()
+    }
+
+    @Test
+    fun deletingATaskDeletesItsAlarms() {
+        val listId = newList()
+        val taskId = newTask(listId)
+        alarms.replaceForTask(taskId, TaskAlarmEntity(taskId = taskId, minutesBefore = 15))
+        assertThat(alarms.all()).hasSize(1)
+
+        tasks.delete(taskId)
+
+        assertThat(alarms.all()).isEmpty()
+    }
+
+    @Test
+    fun deletingAnAccountDetachesItsListsInsteadOfDeletingThem() {
+        val accountId = accounts.insert(AccountEntity(displayName = "Fastmail"))
+        val listId = newList(accountId = accountId)
+
+        accounts.delete(accountId)
+
+        assertThat(lists.entity(listId)!!.accountId).isNull()
+    }
+
+    @Test
+    fun replacingAnAlarmLeavesOnlyTheNewOne() {
+        val listId = newList()
+        val taskId = newTask(listId)
+        alarms.replaceForTask(taskId, TaskAlarmEntity(taskId = taskId, minutesBefore = 15))
+        alarms.replaceForTask(taskId, TaskAlarmEntity(taskId = taskId, minutesBefore = 30))
+
+        assertThat(alarms.forTask(taskId).map { it.minutesBefore }).containsExactly(30)
+        assertThat(alarms.forTask(taskId).single().reference).isEqualTo(AlarmReference.DUE)
+
+        alarms.replaceForTask(taskId, null)
+        assertThat(alarms.forTask(taskId)).isEmpty()
+    }
+
+    // --- the unique index -----------------------------------------------------
+
+    @Test
+    fun anOverrideMayShareItsMastersUid() {
+        val listId = newList()
+        val master = newTask(listId, uid = "series")
+        newTask(listId, uid = "series", masterId = master, recurrenceId = Instant.fromEpochMilliseconds(1))
+        newTask(listId, uid = "series", masterId = master, recurrenceId = Instant.fromEpochMilliseconds(2))
+
+        assertThat(tasks.overrides(master)).hasSize(2)
+    }
+
+    @Test
+    fun rejectsTwoOverridesOfTheSameOccurrence() {
+        val listId = newList()
+        val master = newTask(listId, uid = "series")
+        val at = Instant.fromEpochMilliseconds(1)
+        newTask(listId, uid = "series", masterId = master, recurrenceId = at)
+
+        val failure = runCatching {
+            newTask(listId, uid = "series", masterId = master, recurrenceId = at)
+        }.exceptionOrNull()
+
+        assertThat(failure).isNotNull()
+        assertThat(failure!!.message).contains("UNIQUE")
+    }
+
+    @Test
+    fun theSameUidMayExistInAnotherList() {
+        val a = newList("A")
+        val b = newList("B")
+        newTask(a, uid = "shared")
+        newTask(b, uid = "shared")
+
+        assertThat(tasks.byUid(a, "shared")).isNotNull()
+        assertThat(tasks.byUid(b, "shared")).isNotNull()
+    }
+
+    private companion object {
+        var counter = 0
+    }
+}

app/src/main/AndroidManifest.xml

@@ -2,9 +2,15 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools">
 
-    <!-- Tasks provider access. Both permission sets are declared; the active one
+    <!-- External tasks-provider access, for StorageMode.EXTERNAL only. Both
+         permission sets are declared, since the manifest is static; the active one
          (org.tasks.* for tasks.org, org.dmfs.* for OpenTasks) is requested at
-         runtime by the permission flow. Both are dangerous-level. -->
+         runtime by the permission flow, and only once the user has actually
+         selected External mode. Both are dangerous-level.
+
+         StorageMode.OWN needs nothing here: it is a Room database in our own data
+         directory. Agendula publishes no ContentProvider and declares no
+         permissions of its own. -->
     <uses-permission android:name="org.dmfs.permission.READ_TASKS" />
     <uses-permission android:name="org.dmfs.permission.WRITE_TASKS" />
     <uses-permission android:name="org.tasks.permission.READ_TASKS" />
@@ -74,8 +80,11 @@
             </intent-filter>
         </receiver>
 
-        <!-- Re-sync reminders when the provider changes (external DAVx5 sync).
-             Targets both known authorities; the host must be static. -->
+        <!-- Re-sync reminders when an external provider changes — DAVx5 pulling
+             tasks while Agendula is backgrounded. External mode only: in OWN mode
+             nothing outside the app can change our data, and Room's
+             InvalidationTracker covers our own writes. An intent-filter host must
+             be a literal, so both external authorities are listed. -->
         <receiver
             android:name=".data.reminders.ProviderChangeReceiver"
             android:exported="true">

app/src/main/java/de/jeanlucmakiola/agendula/AgendulaApp.kt

@@ -1,18 +1,22 @@
 package de.jeanlucmakiola.agendula
 
 import android.app.Application
+import androidx.lifecycle.ProcessLifecycleOwner
 import dagger.hilt.EntryPoint
 import dagger.hilt.InstallIn
 import dagger.hilt.android.EntryPointAccessors
 import dagger.hilt.android.HiltAndroidApp
 import dagger.hilt.components.SingletonComponent
+import de.jeanlucmakiola.agendula.data.di.ApplicationScope
 import de.jeanlucmakiola.agendula.data.reminders.ReminderScheduler
+import de.jeanlucmakiola.agendula.data.tasks.ProviderResolver
+import de.jeanlucmakiola.agendula.data.tasks.StartupGate
+import de.jeanlucmakiola.agendula.data.tasks.room.DatabaseCheckpoint
 import de.jeanlucmakiola.floret.crash.CrashConfig
 import de.jeanlucmakiola.floret.crash.CrashReporter
 import kotlinx.coroutines.CoroutineScope
-import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.SupervisorJob
 import kotlinx.coroutines.launch
+import java.util.concurrent.atomic.AtomicBoolean
 
 /**
  * Application entry point. Registered as android:name=".AgendulaApp". Besides
@@ -35,17 +39,42 @@ class AgendulaApp : Application() {
                 issueTitle = getString(R.string.crash_report_issue_title),
             ),
         )
-        val scheduler = EntryPointAccessors
-            .fromApplication(this, ReminderEntryPoint::class.java)
-            .reminderScheduler()
-        CoroutineScope(SupervisorJob() + Dispatchers.Default).launch {
-            runCatching { scheduler.sync() }
+        val entryPoint = EntryPointAccessors.fromApplication(this, AppEntryPoint::class.java)
+        val scheduler = entryPoint.reminderScheduler()
+        // Mirror the stored storage mode into ProviderResolver and import a
+        // v0.3.x install's tasks, both before anything reads a store.
+        val startupGate = entryPoint.startupGate()
+        val scope = entryPoint.applicationScope()
+        // An alarm is armed off whichever store was active when it was scheduled,
+        // so a switch has to rebuild the set. Armed only once startup's own
+        // null -> stored transition is past, which the launch sync below covers.
+        val started = AtomicBoolean(false)
+        entryPoint.providerResolver().onModeChanged {
+            if (started.get()) scope.launch { runCatching { scheduler.sync() } }
+        }
+        startupGate.start()
+        ProcessLifecycleOwner.get().lifecycle.addObserver(entryPoint.databaseCheckpoint())
+        scope.launch {
+            // Wait for the stored mode and the import to land first. Rescheduling
+            // alarms against whichever store autoMode happens to pick would arm
+            // them off the wrong one — or off an empty one, mid-import.
+            runCatching {
+                startupGate.awaitReady()
+                started.set(true)
+                scheduler.sync()
+            }
         }
     }
 
     @EntryPoint
     @InstallIn(SingletonComponent::class)
-    interface ReminderEntryPoint {
+    interface AppEntryPoint {
         fun reminderScheduler(): ReminderScheduler
+        fun startupGate(): StartupGate
+        fun providerResolver(): ProviderResolver
+
+        @ApplicationScope
+        fun applicationScope(): CoroutineScope
+        fun databaseCheckpoint(): DatabaseCheckpoint
     }
 }

app/src/main/java/de/jeanlucmakiola/agendula/data/demo/DemoSeeder.kt

@@ -50,7 +50,7 @@ class DemoSeeder @Inject constructor(
         repository.createTask(TaskForm(title = "Sketch the Agendula app icon", listId = listId))
 
         val done = repository.createTask(TaskForm(title = "Renew domain name", listId = listId, due = at(ts - 2 * day)))
-        repository.setCompleted(done, completed = true)
+        repository.setCompleted(done, occurrenceStart = null, completed = true)
     }
 
     private companion object {

app/src/main/java/de/jeanlucmakiola/agendula/data/di/DataModule.kt

@@ -3,6 +3,8 @@ package de.jeanlucmakiola.agendula.data.di
 import android.content.Context
 import androidx.datastore.core.DataStore
 import androidx.datastore.preferences.core.Preferences
+import androidx.room.Room
+import androidx.room.RoomDatabase
 import androidx.datastore.preferences.preferencesDataStore
 import dagger.Binds
 import dagger.Module
@@ -10,12 +12,21 @@ import dagger.Provides
 import dagger.hilt.InstallIn
 import dagger.hilt.android.qualifiers.ApplicationContext
 import dagger.hilt.components.SingletonComponent
+import de.jeanlucmakiola.agendula.data.tasks.AndroidProviderEnvironment
 import de.jeanlucmakiola.agendula.data.tasks.AndroidTasksDataSource
+import de.jeanlucmakiola.agendula.data.tasks.ModeRoutingTasksDataSource
+import de.jeanlucmakiola.agendula.data.tasks.ProviderEnvironment
+import de.jeanlucmakiola.agendula.data.tasks.ProviderResolver
 import de.jeanlucmakiola.agendula.data.tasks.TasksDataSource
 import de.jeanlucmakiola.agendula.data.tasks.TasksRepository
 import de.jeanlucmakiola.agendula.data.tasks.TasksRepositoryImpl
+import de.jeanlucmakiola.agendula.data.tasks.room.RoomTasksDataSource
+import de.jeanlucmakiola.agendula.data.tasks.room.TasksDatabase
 import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import javax.inject.Provider
 import javax.inject.Singleton
 
 private val Context.agendulaDataStore: DataStore<Preferences> by preferencesDataStore(
@@ -28,11 +39,11 @@ abstract class DataBindModule {
 
     @Binds
     @Singleton
-    abstract fun bindTasksDataSource(impl: AndroidTasksDataSource): TasksDataSource
+    abstract fun bindTasksRepository(impl: TasksRepositoryImpl): TasksRepository
 
     @Binds
     @Singleton
-    abstract fun bindTasksRepository(impl: TasksRepositoryImpl): TasksRepository
+    abstract fun bindProviderEnvironment(impl: AndroidProviderEnvironment): ProviderEnvironment
 }
 
 @Module
@@ -44,7 +55,41 @@ object DataProvideModule {
     fun provideDataStore(@ApplicationContext context: Context): DataStore<Preferences> =
         context.agendulaDataStore
 
+    @Provides
+    @Singleton
+    fun provideTasksDatabase(@ApplicationContext context: Context): TasksDatabase =
+        Room.databaseBuilder(context, TasksDatabase::class.java, TasksDatabase.NAME)
+            // Room's default, stated rather than assumed: Auto Backup copies files
+            // without checkpointing, so a `-wal` sidecar can hold writes the
+            // backed-up `.db` does not. The backup rules carry all three files and
+            // the app checkpoints on ON_STOP.
+            .setJournalMode(RoomDatabase.JournalMode.WRITE_AHEAD_LOGGING)
+            .build()
+
+    /**
+     * The active store, chosen by [StorageMode].
+     *
+     * Resolved per injection point rather than bound once, because the mode is a
+     * user setting that [de.jeanlucmakiola.agendula.data.tasks.StorageModeHolder]
+     * can change while the process lives. Both implementations are singletons, so
+     * this picks between two long-lived objects rather than building either.
+     */
+    @Provides
+    @Singleton
+    fun provideTasksDataSource(
+        resolver: ProviderResolver,
+        room: Provider<RoomTasksDataSource>,
+        external: Provider<AndroidTasksDataSource>,
+    ): TasksDataSource = ModeRoutingTasksDataSource(resolver, room, external)
+
     @Provides
     @IoDispatcher
     fun provideIoDispatcher(): CoroutineDispatcher = Dispatchers.IO
+
+    @Provides
+    @Singleton
+    @ApplicationScope
+    fun provideApplicationScope(): CoroutineScope =
+        // SupervisorJob so one failing collector can't take the others down with it.
+        CoroutineScope(SupervisorJob() + Dispatchers.Default)
 }

app/src/main/java/de/jeanlucmakiola/agendula/data/di/Qualifiers.kt

@@ -6,3 +6,13 @@ import javax.inject.Qualifier
 @Qualifier
 @Retention(AnnotationRetention.BINARY)
 annotation class IoDispatcher
+
+/**
+ * Marks the process-lifetime [kotlinx.coroutines.CoroutineScope] — for work that
+ * outlives any screen and has nothing to be cancelled by, such as keeping the
+ * selected storage mode mirrored out of DataStore. It is never cancelled, so
+ * don't launch anything unbounded in it.
+ */
+@Qualifier
+@Retention(AnnotationRetention.BINARY)
+annotation class ApplicationScope

app/src/main/java/de/jeanlucmakiola/agendula/data/export/ExportWriter.kt

@@ -0,0 +1,132 @@
+package de.jeanlucmakiola.agendula.data.export
+
+import android.content.Context
+import android.net.Uri
+import androidx.documentfile.provider.DocumentFile
+import dagger.hilt.android.qualifiers.ApplicationContext
+import de.jeanlucmakiola.agendula.data.di.IoDispatcher
+import de.jeanlucmakiola.agendula.domain.export.ExportDocument
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.withContext
+import java.io.IOException
+import java.util.zip.ZipEntry
+import java.util.zip.ZipOutputStream
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/** Where an export ended up, for the UI to report. */
+data class ExportResult(val fileCount: Int, val taskListNames: List<String>)
+
+/**
+ * Why an export failed, as a value rather than a message: the UI ships in eleven
+ * locales, so the wording has to come from a string resource.
+ */
+enum class ExportFailure {
+    FOLDER_UNAVAILABLE,
+    FOLDER_NOT_WRITABLE,
+    CANNOT_CREATE_FILE,
+    LOST_ACCESS,
+    WRITE_FAILED,
+}
+
+/** The export could not be written. */
+class ExportFailedException(
+    val failure: ExportFailure,
+    cause: Throwable? = null,
+) : IOException(failure.name, cause)
+
+/**
+ * Writes [ExportDocument]s to a user-chosen location through the Storage Access
+ * Framework.
+ *
+ * No storage permission anywhere: SAF hands us a `Uri` the user picked
+ * themselves, which is both the modern approach and the only one that still works
+ * on scoped storage. The caller owns launching `ACTION_CREATE_DOCUMENT` (for
+ * [writeZip]) or `ACTION_OPEN_DOCUMENT_TREE` (for [writeToTree]) and passes the
+ * result here.
+ *
+ * Marked in `docs/STORAGE-AND-SYNC.md` as floret-kit material — the plumbing is
+ * not task-domain and Calendula will want the same thing. Kept app-local for now
+ * on the kit's own stated principle of not extracting until a second consumer
+ * actually exists; the seam is here, so moving it later is a file move.
+ */
+@Singleton
+class ExportWriter @Inject constructor(
+    @ApplicationContext private val context: Context,
+    @IoDispatcher private val io: CoroutineDispatcher,
+) {
+
+    /**
+     * Writes every document into [treeUri], a directory the user picked.
+     *
+     * A same-named file is truncated and rewritten in place rather than deleted
+     * and recreated: SAF would otherwise append " (1)" and turn the folder into
+     * an unusable pile of snapshots, and a delete that is not followed by a
+     * successful create loses the previous export outright.
+     *
+     * The directory is listed once. `DocumentFile.findFile` queries the whole
+     * tree per call, so looking each name up in the loop is one full
+     * cross-process directory scan per list.
+     */
+    suspend fun writeToTree(treeUri: Uri, documents: List<ExportDocument>): ExportResult =
+        withContext(io) {
+            runCatching {
+                val tree = DocumentFile.fromTreeUri(context, treeUri)
+                    ?: throw ExportFailedException(ExportFailure.FOLDER_UNAVAILABLE)
+                if (!tree.canWrite()) throw ExportFailedException(ExportFailure.FOLDER_NOT_WRITABLE)
+                val existing = tree.listFiles().associateBy { it.name }
+
+                documents.forEach { document ->
+                    val file = existing[document.fileName]
+                        ?: tree.createFile(MIME_ICALENDAR, document.fileName)
+                        ?: throw ExportFailedException(ExportFailure.CANNOT_CREATE_FILE)
+                    write(file.uri, document.content)
+                }
+            }.getOrElse { throw asExportFailure(it) }
+            ExportResult(documents.size, documents.map { it.fileName })
+        }
+
+    /**
+     * Writes every document into a single zip at [target].
+     *
+     * The one-file form, for sharing or for a backup the user filed somewhere
+     * themselves — one attachment rather than one per list.
+     */
+    suspend fun writeZip(target: Uri, documents: List<ExportDocument>): ExportResult =
+        withContext(io) {
+            runCatching {
+                context.contentResolver.openOutputStream(target, "wt")?.use { raw ->
+                    ZipOutputStream(raw.buffered()).use { zip ->
+                        documents.forEach { document ->
+                            zip.putNextEntry(ZipEntry(document.fileName))
+                            zip.write(document.content)
+                            zip.closeEntry()
+                        }
+                    }
+                } ?: throw ExportFailedException(ExportFailure.WRITE_FAILED)
+            }.getOrElse { throw asExportFailure(it) }
+            ExportResult(documents.size, documents.map { it.fileName })
+        }
+
+    private fun write(target: Uri, bytes: ByteArray) {
+        runCatching {
+            // "wt" truncates. Without it a shorter export leaves the tail of the
+            // previous, longer one behind and produces a corrupt file.
+            context.contentResolver.openOutputStream(target, "wt")?.use { it.write(bytes) }
+                ?: throw ExportFailedException(ExportFailure.WRITE_FAILED)
+        }.getOrElse { throw asExportFailure(it) }
+    }
+
+    private fun asExportFailure(cause: Throwable): Throwable = when (cause) {
+        is ExportFailedException -> cause
+        // A SAF grant can be revoked between the picker and the write (the volume
+        // was unmounted, the provider's process died, the user cleared the grant).
+        is SecurityException -> ExportFailedException(ExportFailure.LOST_ACCESS, cause)
+        is IOException -> ExportFailedException(ExportFailure.WRITE_FAILED, cause)
+        else -> cause
+    }
+
+    private companion object {
+        const val MIME_ICALENDAR = "text/calendar"
+    }
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/export/TaskExporter.kt

@@ -0,0 +1,76 @@
+package de.jeanlucmakiola.agendula.data.export
+
+import de.jeanlucmakiola.agendula.data.di.IoDispatcher
+import de.jeanlucmakiola.agendula.data.tasks.TasksDataSource
+import de.jeanlucmakiola.agendula.domain.export.ExportDocument
+import de.jeanlucmakiola.agendula.domain.export.ExportList
+import de.jeanlucmakiola.agendula.domain.export.ICalendarWriter
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.withContext
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Turns the user's task lists into `.ics` documents.
+ *
+ * Export is a v1 feature rather than a nicety because of where the data now
+ * lives: our own provider is inside the app's private storage, so in Local mode a
+ * user's tasks exist in exactly one place and uninstalling deletes them. On Play,
+ * where most people will never have a sync engine, that is the majority case.
+ *
+ * **One document per list**, because a list is a CalDAV collection and that is the
+ * unit every other client understands. Bundling everything into a single file
+ * would flatten the lists away, and list membership is not recoverable from a
+ * VTODO afterwards.
+ */
+@Singleton
+class TaskExporter @Inject constructor(
+    private val dataSource: TasksDataSource,
+    @IoDispatcher private val io: CoroutineDispatcher,
+) {
+
+    /**
+     * Serialises [listIds] — every visible list when null.
+     *
+     * A list with no tasks still produces a document. An empty `.ics` is a real
+     * answer ("this list is empty"), whereas a missing file is indistinguishable
+     * from the export having gone wrong.
+     */
+    suspend fun export(listIds: Set<Long>? = null): List<ExportDocument> = withContext(io) {
+        dataSource.taskLists()
+            .filter { listIds == null || it.id in listIds }
+            .map { list ->
+                val document = ExportList(
+                    listId = list.id,
+                    name = list.name,
+                    accountName = list.accountName,
+                    tasks = dataSource.exportTasks(list.id),
+                )
+                ExportDocument(
+                    fileName = fileNameFor(list.name, list.id),
+                    content = ICalendarWriter.write(document).toByteArray(Charsets.UTF_8),
+                )
+            }
+    }
+
+    companion object {
+
+        /**
+         * A file name derived from the list name, safe on every filesystem the
+         * user might pick through SAF (including FAT32 on an SD card).
+         *
+         * The list id is appended rather than trusted to be redundant: two lists on
+         * different accounts may share a name, and two exports landing on the same
+         * file would silently lose one of them.
+         */
+        fun fileNameFor(listName: String, listId: Long): String {
+            val safe = listName
+                .map { if (it.isLetterOrDigit() || it == '-' || it == '_') it else '-' }
+                .joinToString("")
+                .trim('-')
+                .take(60)
+                .ifBlank { "list" }
+            return "$safe-$listId.ics"
+        }
+    }
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/prefs/SettingsPrefs.kt

@@ -8,11 +8,12 @@ import androidx.datastore.preferences.core.intPreferencesKey
 import androidx.datastore.preferences.core.longPreferencesKey
 import androidx.datastore.preferences.core.stringPreferencesKey
 import androidx.datastore.preferences.core.stringSetPreferencesKey
+import de.jeanlucmakiola.agendula.data.tasks.StorageMode
 import de.jeanlucmakiola.agendula.domain.TaskFormField
 import de.jeanlucmakiola.floret.reminders.ReminderOverride
 import de.jeanlucmakiola.floret.reminders.ReminderOverrideCodec
 import de.jeanlucmakiola.floret.reminders.applyReminderOverride
-import de.jeanlucmakiola.floret.reminders.reminderLeadFor
+import de.jeanlucmakiola.floret.reminders.reminderLeadsFor
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.map
 import javax.inject.Inject
@@ -39,15 +40,17 @@ data class Settings(
     val bottomAddBar: Boolean = false,
     /**
      * Per-list overrides of [reminderLeadMinutes]: a list present in the map
-     * overrides the global default (a null value = no reminder); absent = inherit.
+     * overrides the global default (an empty list = no reminder); absent =
+     * inherit. Agendula offers a single reminder, so each override is a
+     * one-element (or empty) list.
      */
-    val perListReminderOverride: Map<Long, Int?> = emptyMap(),
+    val perListReminderOverride: Map<Long, List<Int>> = emptyMap(),
     /** Optional edit-form fields shown by default; the rest sit behind "More fields". */
     val defaultEditFields: Set<TaskFormField> = emptySet(),
 ) {
     /** The lead time for a task in [listId]: its override if set, else the global default. */
     fun reminderLeadFor(listId: Long): Int? =
-        perListReminderOverride.reminderLeadFor(listId, reminderLeadMinutes)
+        perListReminderOverride.reminderLeadsFor(listId, listOf(reminderLeadMinutes)).firstOrNull()
 }
 
 /** App preferences, backed by DataStore. Mirrors Calendula's prefs shape. */
@@ -80,6 +83,31 @@ class SettingsPrefs @Inject constructor(
 
     suspend fun setReminderLeadMinutes(minutes: Int) = dataStore.edit { it[REMINDER_LEAD] = minutes }
 
+    /**
+     * Which task store backs the app, or `null` while the user has not chosen —
+     * which is the normal state, since most people never open Settings.
+     *
+     * Kept out of [Settings] on purpose. Everything in there is a rendering
+     * preference collected by the UI; this one selects an authority in the data
+     * layer, is read on paths that must not wait for a whole settings object, and
+     * `null` genuinely means "undecided" rather than "default" — the difference
+     * matters, because undecided is what lets `ProviderResolver.autoMode` keep an
+     * upgrading Posture A user pointed at the provider that holds their data.
+     */
+    val storageMode: Flow<StorageMode?> = dataStore.data.map { p ->
+        when (val stored = p[STORAGE_MODE]) {
+            null -> null
+            // 0.3.x's value for the bundled dmfs provider. That store is gone and
+            // its data was imported into OWN, so read it as OWN rather than
+            // letting it fall through to autoMode — someone who chose local
+            // storage explicitly would otherwise be sent to an external provider.
+            "LOCAL" -> StorageMode.OWN
+            else -> runCatching { StorageMode.valueOf(stored) }.getOrNull()
+        }
+    }
+
+    suspend fun setStorageMode(mode: StorageMode) = dataStore.edit { it[STORAGE_MODE] = mode.name }
+
     /** One-time reminder onboarding gate; false until the step has been shown. */
     val reminderOnboardingDone: Flow<Boolean> = dataStore.data.map { it[REMINDER_ONBOARDING_DONE] ?: false }
 
@@ -111,6 +139,7 @@ class SettingsPrefs @Inject constructor(
         val SHOW_ADD_SUBTASK_ROW = booleanPreferencesKey("show_add_subtask_row")
         val BOTTOM_ADD_BAR = booleanPreferencesKey("bottom_add_bar")
         val REMINDER_ONBOARDING_DONE = booleanPreferencesKey("reminder_onboarding_done")
+        val STORAGE_MODE = stringPreferencesKey("storage_mode")
         val LIST_REMINDER_OVERRIDE = stringPreferencesKey("list_reminder_override")
         val DEFAULT_EDIT_FIELDS = stringSetPreferencesKey("default_edit_fields")
     }

app/src/main/java/de/jeanlucmakiola/agendula/data/reminders/DueReminderReceiver.kt

@@ -3,6 +3,7 @@ package de.jeanlucmakiola.agendula.data.reminders
 import android.content.BroadcastReceiver
 import android.content.Context
 import android.content.Intent
+import androidx.core.net.toUri
 import dagger.hilt.android.AndroidEntryPoint
 import de.jeanlucmakiola.agendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.agendula.data.tasks.TasksDataSource
@@ -45,7 +46,14 @@ class DueReminderReceiver : BroadcastReceiver() {
     companion object {
         private const val EXTRA_TASK_ID = "de.jeanlucmakiola.agendula.extra.TASK_ID"
 
-        fun intent(context: Context, taskId: Long): Intent =
-            Intent(context, DueReminderReceiver::class.java).putExtra(EXTRA_TASK_ID, taskId)
+        /**
+         * [triggerAt] rides in the intent *data*, not just an extra: PendingIntent
+         * identity ignores extras, so two occurrences of the same recurring task
+         * would otherwise collapse into one alarm under FLAG_UPDATE_CURRENT.
+         */
+        fun intent(context: Context, taskId: Long, triggerAt: Long): Intent =
+            Intent(context, DueReminderReceiver::class.java)
+                .setData("agendula://reminder/$taskId/$triggerAt".toUri())
+                .putExtra(EXTRA_TASK_ID, taskId)
     }
 }

app/src/main/java/de/jeanlucmakiola/agendula/data/reminders/ProviderChangeReceiver.kt

@@ -3,7 +3,9 @@ package de.jeanlucmakiola.agendula.data.reminders
 import android.content.BroadcastReceiver
 import android.content.Context
 import android.content.Intent
+import android.os.SystemClock
 import dagger.hilt.android.AndroidEntryPoint
+import de.jeanlucmakiola.agendula.data.tasks.ProviderResolver
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.SupervisorJob
@@ -20,10 +22,25 @@ import javax.inject.Inject
 class ProviderChangeReceiver : BroadcastReceiver() {
 
     @Inject lateinit var scheduler: ReminderScheduler
+    @Inject lateinit var providerResolver: ProviderResolver
 
     private val scope = CoroutineScope(SupervisorJob() + Dispatchers.Default)
 
     override fun onReceive(context: Context, intent: Intent) {
+        // The receiver has to stay exported to hear the provider's broadcast, and
+        // the sender holds no permission we could require — so validate the
+        // broadcast itself. Without this, any installed app can spam a full
+        // re-sync (an unbounded provider read) by firing a matching intent.
+        if (intent.action != Intent.ACTION_PROVIDER_CHANGED) return
+        val authority = providerResolver.resolve()?.authority ?: return
+        if (intent.data?.host != authority) return
+        // External sync can fire these in bursts; one re-sync per burst is plenty.
+        val now = SystemClock.elapsedRealtime()
+        synchronized(Companion) {
+            if (now - lastSyncAt < MIN_SYNC_INTERVAL_MS) return
+            lastSyncAt = now
+        }
+
         val pending = goAsync()
         scope.launch {
             try {
@@ -33,4 +50,11 @@ class ProviderChangeReceiver : BroadcastReceiver() {
             }
         }
     }
+
+    private companion object {
+        const val MIN_SYNC_INTERVAL_MS = 10_000L
+
+        @Volatile
+        var lastSyncAt = -MIN_SYNC_INTERVAL_MS
+    }
 }

app/src/main/java/de/jeanlucmakiola/agendula/data/reminders/ReminderScheduler.kt

@@ -12,15 +12,18 @@ import de.jeanlucmakiola.agendula.data.tasks.TaskQuery
 import de.jeanlucmakiola.agendula.data.tasks.TasksDataSource
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import kotlinx.coroutines.withContext
 import javax.inject.Inject
 import javax.inject.Singleton
 
 /**
- * The self-scheduled due-reminder engine. Tasks providers don't deliver
- * reminders, so Agendula reads upcoming due tasks and arms one exact [AlarmManager]
- * alarm each, within a rolling window. Re-run on app start, boot and provider
- * change; it diffs against [ScheduledReminderStore] so only changed alarms move.
+ * The self-scheduled due-reminder engine. Nothing else delivers task reminders —
+ * not the platform, not a tasks provider — so Agendula reads upcoming due tasks
+ * and arms one exact [AlarmManager] alarm each, within a rolling window. Re-run
+ * on app start, on boot, on a store switch, and on an external provider change;
+ * it diffs against [ScheduledReminderStore] so only changed alarms move.
  */
 @Singleton
 class ReminderScheduler @Inject constructor(
@@ -31,47 +34,89 @@ class ReminderScheduler @Inject constructor(
     private val providerResolver: ProviderResolver,
     @IoDispatcher private val io: CoroutineDispatcher,
 ) {
-    suspend fun sync() = withContext(io) {
-        val provider = providerResolver.resolve()
+    private val syncLock = Mutex()
+
+    /**
+     * Diff the armed alarms against the store and move only what changed.
+     *
+     * Serialised: the diff is a read-modify-write over [ScheduledReminderStore],
+     * and callers overlap (a store switch fires this while the launch sync may
+     * still be running). Two interleaved runs would each write their own set as
+     * the whole truth, leaving the other's alarms armed but unrecorded — never
+     * cancelled, and firing against the wrong store's task ids.
+     */
+    suspend fun sync() = withContext(io) { syncLock.withLock { syncLocked() } }
+
+    private suspend fun syncLocked() {
         val settings = settingsPrefs.settings.first()
-        if (provider == null || !providerResolver.hasPermission(provider) || !settings.remindersEnabled) {
+        // Gate on whether the store is readable, not on whether a provider
+        // resolves: our own store deliberately resolves to no provider, so the
+        // latter clears every reminder in the default mode.
+        if (!settings.remindersEnabled || !providerResolver.canReadStore()) {
             clearAll()
-            return@withContext
+            return
         }
         val now = System.currentTimeMillis()
         val horizon = now + WINDOW_MS
         val tasks = runCatching { dataSource.tasks(TaskQuery(includeCompleted = false)) }
-            .getOrElse { return@withContext }
+            .getOrElse { return }
+
+        // One reminder per *occurrence*: a recurring series yields a row per
+        // occurrence, all sharing a taskId, so this is a Set rather than a
+        // taskId-keyed Map — keying by task would collapse a daily recurring task
+        // down to one arbitrary reminder.
+        // Per-task leads. One query for all of them.
+        val perTask = runCatching { dataSource.alarms() }.getOrElse { emptyMap() }
 
         val desired = tasks
             .filter { !it.isClosed && it.due != null }
             .mapNotNull { task ->
-                // The task's list may override the global lead, or opt out entirely
-                // (override = null), in which case it gets no reminder at all.
-                val lead = settings.reminderLeadFor(task.listId) ?: return@mapNotNull null
-                task.taskId to (task.due!!.toEpochMilliseconds() - lead.coerceAtLeast(0) * 60_000L)
+                // A reminder set on the task itself wins; otherwise the task's list
+                // may override the global lead, or opt out entirely (override =
+                // null), in which case it gets no reminder at all.
+                val reminder = perTask[task.taskId]
+                val lead = reminder?.minutesBefore
+                    ?: settings.reminderLeadFor(task.listId)
+                    ?: return@mapNotNull null
+                // A stored reminder says what it counts back from. Ours are always
+                // before due, but an imported dmfs alarm or another client's can be
+                // before *start* — firing those off the due date is silently wrong
+                // for every task whose start and due differ.
+                val anchor = if (reminder?.fromStart == true) task.start ?: task.due!! else task.due!!
+                ScheduledReminder(
+                    taskId = task.taskId,
+                    triggerAt = anchor.toEpochMilliseconds() - lead.coerceAtLeast(0) * 60_000L,
+                )
             }
-            .toMap()
-            .filterValues { it in now..horizon }
+            // The lower bound trails `now` so a reminder missed while the device was
+            // off still fires once on boot instead of being silently dropped —
+            // setExactAndAllowWhileIdle delivers a past trigger immediately. Anything
+            // already armed stays armed (the diff below), so it can't re-fire.
+            .filter { it.triggerAt in (now - MISSED_GRACE_MS)..horizon }
+            .toSet()
 
         val previous = store.all()
-        (previous.keys - desired.keys).forEach { cancel(it) }
-        desired.forEach { (taskId, triggerAt) ->
-            if (previous[taskId] != triggerAt) schedule(taskId, triggerAt)
-        }
+        (previous - desired).forEach { cancel(it) }
+        (desired - previous).forEach { schedule(it) }
         store.replace(desired)
     }
 
     private fun alarmManager(): AlarmManager = context.getSystemService(AlarmManager::class.java)
 
-    private fun pendingIntent(taskId: Long, create: Boolean): PendingIntent? {
+    private fun pendingIntent(reminder: ScheduledReminder, create: Boolean): PendingIntent? {
         val flags = (if (create) PendingIntent.FLAG_UPDATE_CURRENT else PendingIntent.FLAG_NO_CREATE) or
             PendingIntent.FLAG_IMMUTABLE
-        return PendingIntent.getBroadcast(context, taskId.toInt(), DueReminderReceiver.intent(context, taskId), flags)
+        return PendingIntent.getBroadcast(
+            context,
+            reminder.requestCode,
+            DueReminderReceiver.intent(context, reminder.taskId, reminder.triggerAt),
+            flags,
+        )
     }
 
-    private fun schedule(taskId: Long, triggerAt: Long) {
-        val pi = pendingIntent(taskId, create = true) ?: return
+    private fun schedule(reminder: ScheduledReminder) {
+        val triggerAt = reminder.triggerAt
+        val pi = pendingIntent(reminder, create = true) ?: return
         val am = alarmManager()
         val canExact = Build.VERSION.SDK_INT < Build.VERSION_CODES.S || am.canScheduleExactAlarms()
         if (canExact) {
@@ -81,19 +126,21 @@ class ReminderScheduler @Inject constructor(
         }
     }
 
-    private fun cancel(taskId: Long) {
-        pendingIntent(taskId, create = false)?.let {
+    private fun cancel(reminder: ScheduledReminder) {
+        pendingIntent(reminder, create = false)?.let {
             alarmManager().cancel(it)
             it.cancel()
         }
     }
 
     private suspend fun clearAll() {
-        store.all().keys.forEach { cancel(it) }
-        store.replace(emptyMap())
+        store.all().forEach { cancel(it) }
+        store.replace(emptySet())
     }
 
     private companion object {
         const val WINDOW_MS = 30L * 24 * 60 * 60 * 1000 // 30 days
+        /** How long after its trigger a missed reminder is still worth firing. */
+        const val MISSED_GRACE_MS = 6L * 60 * 60 * 1000 // 6 hours
     }
 }

app/src/main/java/de/jeanlucmakiola/agendula/data/reminders/ScheduledReminderStore.kt

@@ -9,25 +9,38 @@ import javax.inject.Inject
 import javax.inject.Singleton
 
 /**
- * Remembers which task reminders are currently scheduled (taskId → trigger time),
- * so [ReminderScheduler] can diff against a fresh computation and cancel only the
- * alarms that changed. Persisted in DataStore as a set of `taskId|trigger` strings.
+ * One armed alarm. A recurring task has many occurrences sharing a [taskId], so
+ * the trigger time is part of the identity — keying by task alone would collapse
+ * a daily task down to a single reminder.
+ */
+data class ScheduledReminder(val taskId: Long, val triggerAt: Long) {
+    /**
+     * Request code for this alarm's PendingIntent. Derived from both fields so
+     * sibling occurrences don't share (and overwrite) one alarm slot.
+     */
+    val requestCode: Int get() = (taskId * 31 + triggerAt).hashCode()
+}
+
+/**
+ * Remembers which task reminders are currently armed, so [ReminderScheduler] can
+ * diff against a fresh computation and touch only the alarms that changed.
+ * Persisted in DataStore as a set of `taskId|trigger` strings.
  */
 @Singleton
 class ScheduledReminderStore @Inject constructor(
     private val dataStore: DataStore<Preferences>,
 ) {
-    suspend fun all(): Map<Long, Long> =
+    suspend fun all(): Set<ScheduledReminder> =
         dataStore.data.first()[KEY].orEmpty().mapNotNull { entry ->
             val parts = entry.split('|')
             val id = parts.getOrNull(0)?.toLongOrNull()
             val at = parts.getOrNull(1)?.toLongOrNull()
-            if (id != null && at != null) id to at else null
-        }.toMap()
+            if (id != null && at != null) ScheduledReminder(id, at) else null
+        }.toSet()
 
-    suspend fun replace(scheduled: Map<Long, Long>) {
+    suspend fun replace(scheduled: Set<ScheduledReminder>) {
         dataStore.edit { prefs ->
-            prefs[KEY] = scheduled.entries.map { "${it.key}|${it.value}" }.toSet()
+            prefs[KEY] = scheduled.map { "${it.taskId}|${it.triggerAt}" }.toSet()
         }
     }
 

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/AndroidTasksDataSource.kt

@@ -11,13 +11,16 @@ import android.os.Looper
 import dagger.hilt.android.qualifiers.ApplicationContext
 import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Instances
 import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Lists
+import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Properties
 import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Tasks
 import de.jeanlucmakiola.agendula.domain.Task
 import de.jeanlucmakiola.agendula.domain.TaskForm
 import de.jeanlucmakiola.agendula.domain.TaskList
+import de.jeanlucmakiola.agendula.domain.export.ExportTask
 import java.time.ZoneId
 import javax.inject.Inject
 import javax.inject.Singleton
+import kotlin.time.Instant
 
 /**
  * The only class that knows about the ContentResolver, [TasksContract] and the
@@ -83,6 +86,26 @@ class AndroidTasksDataSource @Inject constructor(
             } ?: emptyList()
     }
 
+    override fun exportTasks(listId: Long): List<ExportTask> {
+        // projection = null for the same reason queryInstances uses it: the tasks
+        // table's shape varies across provider versions, and the by-name mapper
+        // reads what's there.
+        val uri = TasksContract.tasksUri(authority())
+        return resolver.query(
+            uri,
+            null,
+            // _deleted marks a row awaiting a sync round-trip. It's gone as far as
+            // the user is concerned, so exporting it would resurrect deleted tasks
+            // in the backup.
+            "${Tasks.LIST_ID} = ? AND (${Tasks.DELETED} IS NULL OR ${Tasks.DELETED} = 0)",
+            arrayOf(listId.toString()),
+            null,
+        )?.use { c ->
+            val reader = CursorColumnReader(c)
+            buildList { while (c.moveToNext()) add(TaskMapper.exportTask(reader)) }
+        } ?: emptyList()
+    }
+
     // --- writes ---------------------------------------------------------------
 
     override fun insertTask(form: TaskForm): Long {
@@ -98,12 +121,109 @@ class AndroidTasksDataSource @Inject constructor(
         if (rows == 0) throw TaskWriteFailedException("update task $taskId")
     }
 
+    override fun updateInstance(taskId: Long, occurrenceStart: Instant, form: TaskForm) {
+        val instanceId = instanceIdFor(taskId, occurrenceStart)
+            ?: throw TaskWriteFailedException("update instance $taskId@$occurrenceStart: no such occurrence")
+        val values = TaskWriteMapper.instanceValues(form, ZoneId.systemDefault().id)
+        val uri = TasksContract.instanceUri(authority(), instanceId)
+        val rows = resolver.update(uri, values.toContentValues(), null, null)
+        if (rows == 0) throw TaskWriteFailedException("update instance $instanceId")
+    }
+
+    /**
+     * The provider's instance row id for one occurrence.
+     *
+     * The seam addresses occurrences by `(taskId, occurrenceStart)`; writing
+     * through the instances URI still needs the row id, so it is looked up here
+     * rather than carried around above the data layer. Selection is on `task_id`
+     * only — the anchor is matched in Kotlin because the column that holds it
+     * (`instance_original_time`) is missing on older provider schemas, where a
+     * WHERE clause naming it would throw instead of falling back.
+     */
+    private fun instanceIdFor(taskId: Long, occurrenceStart: Instant): Long? {
+        val uri = TasksContract.instancesUri(authority())
+        val selection = "${Instances.TASK_ID} = ?"
+        return resolver.query(uri, null, selection, arrayOf(taskId.toString()), null)?.use { c ->
+            val reader = CursorColumnReader(c)
+            while (c.moveToNext()) {
+                if (TaskMapper.occurrenceAnchor(reader) == occurrenceStart) {
+                    return@use reader.getLong(Tasks.ID)
+                }
+            }
+            null
+        }
+    }
+
+    override fun setAlarm(taskId: Long, minutesBeforeDue: Int?) {
+        val uri = TasksContract.propertiesUri(authority())
+        // Replace rather than update: the provider's AlarmHandler re-validates the
+        // whole row on every update, so a partial edit throws — and delete+insert
+        // means we never have to track property_id.
+        resolver.delete(
+            uri,
+            "${Properties.TASK_ID} = ? AND ${Properties.MIMETYPE} = ?",
+            arrayOf(taskId.toString(), TasksContract.Alarm.MIMETYPE),
+        )
+        if (minutesBeforeDue != null) {
+            resolver.insert(uri, TaskWriteMapper.alarmValues(taskId, minutesBeforeDue).toContentValues())
+                ?: throw TaskWriteFailedException("set alarm for task $taskId")
+        }
+    }
+
+    override fun alarms(): Map<Long, TaskReminder> {
+        val uri = TasksContract.propertiesUri(authority())
+        val projection = arrayOf(
+            Properties.TASK_ID,
+            TasksContract.Alarm.MINUTES_BEFORE,
+            TasksContract.Alarm.REFERENCE,
+        )
+        return resolver.query(
+            uri,
+            projection,
+            "${Properties.MIMETYPE} = ?",
+            arrayOf(TasksContract.Alarm.MIMETYPE),
+            null,
+        )?.use { c ->
+            val reader = CursorColumnReader(c)
+            buildMap {
+                while (c.moveToNext()) {
+                    val id = reader.getLong(Properties.TASK_ID)
+                    val minutes = reader.getInt(TasksContract.Alarm.MINUTES_BEFORE)
+                    val reference = reader.getInt(TasksContract.Alarm.REFERENCE)
+                    if (id != null && minutes != null) {
+                        put(
+                            id,
+                            TaskReminder(
+                                minutesBefore = minutes,
+                                fromStart = reference == TasksContract.Alarm.REFERENCE_START,
+                            ),
+                        )
+                    }
+                }
+            }
+        } ?: emptyMap()
+    }
+
     override fun setCompleted(taskId: Long, completed: Boolean) {
         val values = TaskWriteMapper.completionValues(completed, System.currentTimeMillis())
         val rows = resolver.update(taskUri(authority(), taskId), values.toContentValues(), null, null)
         if (rows == 0) throw TaskWriteFailedException("complete task $taskId")
     }
 
+    /**
+     * Through the instances URI, which is what makes the provider fork an override
+     * rather than close the series. No instance row for the anchor means the task
+     * is not a series after all — the plain write is then the right one.
+     */
+    override fun setCompletedInstance(taskId: Long, occurrenceStart: Instant, completed: Boolean) {
+        val instanceId = instanceIdFor(taskId, occurrenceStart)
+            ?: return setCompleted(taskId, completed)
+        val values = TaskWriteMapper.completionValues(completed, System.currentTimeMillis())
+        val uri = TasksContract.instanceUri(authority(), instanceId)
+        val rows = resolver.update(uri, values.toContentValues(), null, null)
+        if (rows == 0) throw TaskWriteFailedException("complete instance $instanceId")
+    }
+
     override fun deleteTask(taskId: Long) {
         resolver.delete(taskUri(authority(), taskId), null, null)
     }
@@ -120,6 +240,31 @@ class AndroidTasksDataSource @Inject constructor(
         return result.lastPathSegment?.toLongOrNull() ?: throw TaskWriteFailedException("create local list: no id")
     }
 
+    override fun updateList(listId: Long, name: String, color: Int) {
+        val values = TaskWriteMapper.listValues(name, color)
+        val rows = resolver.update(listSyncUri(listId), values.toContentValues(), null, null)
+        if (rows == 0) throw TaskWriteFailedException("update list $listId")
+    }
+
+    override fun deleteList(listId: Long) {
+        val rows = resolver.delete(listSyncUri(listId), null, null)
+        if (rows == 0) throw TaskWriteFailedException("delete list $listId")
+    }
+
+    /**
+     * A list row addressed as its own account's sync adapter — the provider only
+     * lets that caller write the `tasklists` table, and the account has to be the
+     * row's own (the params are matched against it, not merely accepted).
+     */
+    private fun listSyncUri(listId: Long): Uri {
+        val authority = authority()
+        val uri = TasksContract.listUri(authority, listId)
+        val account = resolver.query(uri, arrayOf(Lists.ACCOUNT_NAME, Lists.ACCOUNT_TYPE), null, null, null)
+            ?.use { c -> if (c.moveToFirst()) c.getString(0).orEmpty() to c.getString(1).orEmpty() else null }
+            ?: throw TaskWriteFailedException("list $listId not found")
+        return TasksContract.asSyncAdapter(uri, account.first, account.second)
+    }
+
     // --- observation ----------------------------------------------------------
 
     override fun registerObserver(onChange: () -> Unit): AutoCloseable {
@@ -127,9 +272,16 @@ class AndroidTasksDataSource @Inject constructor(
         val observer = object : ContentObserver(Handler(Looper.getMainLooper())) {
             override fun onChange(selfChange: Boolean) = onChange()
         }
-        resolver.registerContentObserver(TasksContract.instancesUri(provider.authority), true, observer)
-        resolver.registerContentObserver(TasksContract.listsUri(provider.authority), true, observer)
-        return AutoCloseable { resolver.unregisterContentObserver(observer) }
+        // Register both or neither: if the second call throws, the first
+        // registration would otherwise leak (no AutoCloseable was handed back yet).
+        try {
+            resolver.registerContentObserver(TasksContract.instancesUri(provider.authority), true, observer)
+            resolver.registerContentObserver(TasksContract.listsUri(provider.authority), true, observer)
+        } catch (e: RuntimeException) {
+            runCatching { resolver.unregisterContentObserver(observer) }
+            throw e
+        }
+        return AutoCloseable { runCatching { resolver.unregisterContentObserver(observer) } }
     }
 
     private fun Map<String, Any?>.toContentValues(): ContentValues {

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/ModeRoutingTasksDataSource.kt

@@ -0,0 +1,88 @@
+package de.jeanlucmakiola.agendula.data.tasks
+
+import de.jeanlucmakiola.agendula.data.tasks.room.RoomTasksDataSource
+import de.jeanlucmakiola.agendula.domain.Task
+import de.jeanlucmakiola.agendula.domain.TaskForm
+import de.jeanlucmakiola.agendula.domain.TaskList
+import de.jeanlucmakiola.agendula.domain.export.ExportTask
+import javax.inject.Provider
+import kotlin.time.Instant
+
+/**
+ * Routes every call to the store [StorageMode] selects.
+ *
+ * Per-call rather than bound once: the mode is a setting the user can change
+ * while the process lives, and [StorageModeHolder] pushes the new value into
+ * [ProviderResolver] without rebuilding the object graph. Both delegates are
+ * singletons, so this chooses between two existing objects.
+ *
+ * Room versus a third-party ContentProvider — nothing else.
+ */
+class ModeRoutingTasksDataSource(
+    private val resolver: ProviderResolver,
+    private val room: Provider<RoomTasksDataSource>,
+    private val external: Provider<AndroidTasksDataSource>,
+) : TasksDataSource {
+
+    private fun active(): TasksDataSource =
+        when (resolver.mode()) {
+            StorageMode.OWN -> room.get()
+            StorageMode.EXTERNAL -> external.get()
+        }
+
+    override fun taskLists(): List<TaskList> = active().taskLists()
+    override fun tasks(query: TaskQuery): List<Task> = active().tasks(query)
+    override fun task(taskId: Long): Task? = active().task(taskId)
+    override fun subtasks(parentTaskId: Long): List<Task> = active().subtasks(parentTaskId)
+    override fun insertTask(form: TaskForm): Long = active().insertTask(form)
+    override fun updateTask(taskId: Long, form: TaskForm) = active().updateTask(taskId, form)
+
+    override fun updateInstance(taskId: Long, occurrenceStart: Instant, form: TaskForm) =
+        active().updateInstance(taskId, occurrenceStart, form)
+
+    override fun setAlarm(taskId: Long, minutesBeforeDue: Int?) = active().setAlarm(taskId, minutesBeforeDue)
+    override fun alarms(): Map<Long, TaskReminder> = active().alarms()
+    override fun exportTasks(listId: Long): List<ExportTask> = active().exportTasks(listId)
+    override fun setCompleted(taskId: Long, completed: Boolean) = active().setCompleted(taskId, completed)
+
+    override fun setCompletedInstance(taskId: Long, occurrenceStart: Instant, completed: Boolean) =
+        active().setCompletedInstance(taskId, occurrenceStart, completed)
+
+    override fun deleteTask(taskId: Long) = active().deleteTask(taskId)
+    override fun createLocalList(name: String, color: Int): Long = active().createLocalList(name, color)
+    override fun updateList(listId: Long, name: String, color: Int) = active().updateList(listId, name, color)
+    override fun deleteList(listId: Long) = active().deleteList(listId)
+    /**
+     * Unlike every other method here, an observer is registered once and then
+     * *held* — so it cannot be routed per call, and would otherwise stay bound to
+     * whichever store was active when the flow started. Switching stores in
+     * Settings would then leave every open screen listening to the store it is no
+     * longer reading from.
+     *
+     * So the registration moves with the mode, and the switch itself counts as a
+     * change: the data underneath every live flow has just been replaced.
+     */
+    override fun registerObserver(onChange: () -> Unit): AutoCloseable {
+        val lock = Any()
+        var closed = false
+        var handle: AutoCloseable? = runCatching { active().registerObserver(onChange) }.getOrNull()
+
+        val modeHandle = resolver.onModeChanged {
+            synchronized(lock) {
+                if (!closed) {
+                    handle?.let { runCatching { it.close() } }
+                    handle = runCatching { active().registerObserver(onChange) }.getOrNull()
+                }
+            }
+            onChange()
+        }
+        return AutoCloseable {
+            synchronized(lock) {
+                closed = true
+                modeHandle.close()
+                handle?.let { runCatching { it.close() } }
+                handle = null
+            }
+        }
+    }
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/ProviderEnvironment.kt

@@ -0,0 +1,46 @@
+package de.jeanlucmakiola.agendula.data.tasks
+
+import android.content.Context
+import android.content.pm.PackageManager
+import androidx.core.content.ContextCompat
+import dagger.hilt.android.qualifiers.ApplicationContext
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * The two platform facts [ProviderResolver] needs, behind an interface.
+ *
+ * Same seam the data source uses, for the same reason: which store a returning
+ * user lands on is decided by [ProviderResolver.autoMode], getting it wrong shows
+ * them an empty app, and that decision is worth testing on the JVM rather than
+ * only on a device. Everything Android-shaped lives here so the logic above stays
+ * plain Kotlin.
+ */
+interface ProviderEnvironment {
+
+    /** The package declaring [authority], or `null` when nothing on the device does. */
+    fun packageDeclaring(authority: String): String?
+
+    /** Whether this app currently holds [permission]. */
+    fun isGranted(permission: String): Boolean
+
+    /** [packageName]'s own app name, or null when it cannot be read. */
+    fun appLabel(packageName: String): String?
+}
+
+@Singleton
+class AndroidProviderEnvironment @Inject constructor(
+    @ApplicationContext private val context: Context,
+) : ProviderEnvironment {
+
+    override fun packageDeclaring(authority: String): String? =
+        context.packageManager.resolveContentProvider(authority, 0)?.packageName
+
+    override fun isGranted(permission: String): Boolean =
+        ContextCompat.checkSelfPermission(context, permission) == PackageManager.PERMISSION_GRANTED
+
+    override fun appLabel(packageName: String): String? = runCatching {
+        val pm = context.packageManager
+        pm.getApplicationLabel(pm.getApplicationInfo(packageName, 0)).toString()
+    }.getOrNull()
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/ProviderFlow.kt

@@ -0,0 +1,31 @@
+package de.jeanlucmakiola.agendula.data.tasks
+
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.retryWhen
+
+private const val BASE_RETRY_MS = 1_000L
+private const val MAX_RETRY_MS = 30_000L
+
+/** 1s, 2s, 4s … capped at 30s, so a permanently-absent provider costs little. */
+private fun retryDelayMs(attempt: Long): Long =
+    (BASE_RETRY_MS shl attempt.coerceAtMost(5).toInt()).coerceAtMost(MAX_RETRY_MS)
+
+/**
+ * Recover a provider-backed flow without killing it.
+ *
+ * Provider reads fail for reasons that resolve on their own: the read permission
+ * isn't granted yet (first launch collects before the permission gate), or the
+ * provider app is mid-update. A terminal `catch` swallows the failure *and*
+ * cancels the upstream, so the flow never produces again — the screen stays empty
+ * until the process restarts, even after the user grants the permission.
+ *
+ * This emits [fallback] instead and keeps retrying with a capped backoff, so the
+ * collector recovers on its own once the provider becomes readable.
+ */
+fun <T> Flow<T>.recoveringFromProviderFailure(fallback: () -> T): Flow<T> =
+    retryWhen { _, attempt ->
+        emit(fallback())
+        delay(retryDelayMs(attempt))
+        true
+    }

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/ProviderResolver.kt

@@ -1,15 +1,12 @@
 package de.jeanlucmakiola.agendula.data.tasks
 
-import android.content.Context
-import android.content.pm.PackageManager
-import androidx.core.content.ContextCompat
-import dagger.hilt.android.qualifiers.ApplicationContext
+import java.util.concurrent.CopyOnWriteArrayList
 import javax.inject.Inject
 import javax.inject.Singleton
 
 /**
- * A tasks provider Agendula can talk to. The same dmfs `TaskProvider` backs every
- * candidate, so the [TasksContract] columns apply regardless of which is present.
+ * An external tasks provider Agendula can talk to. Every candidate runs the same
+ * dmfs `TaskProvider`, so the [TasksContract] columns apply to either.
  */
 data class TaskProvider(
     val authority: String,
@@ -19,41 +16,122 @@ data class TaskProvider(
 )
 
 /**
- * The A/B seam. Detects which tasks provider is installed at runtime and which
- * permission set it needs, so nothing above the data layer hardcodes an
- * authority. Under Posture B (bundled provider) this simply finds our own
- * `org.dmfs.tasks` first. See docs/PLAN.md.
+ * Discovers the *external* tasks providers (OpenTasks, tasks.org) that
+ * [StorageMode.EXTERNAL] can be pointed at.
+ *
+ * This used to be the A/B seam between an external provider and one Agendula
+ * bundled itself. That second half is gone: [StorageMode.OWN] is a Room database
+ * with no authority, no ContentResolver and nothing to permit, so there is
+ * nothing here for it to resolve. See `docs/OWN-STORE.md`.
+ *
+ * Which store is active comes from [storageMode]; how that gets decided when the
+ * user has not chosen is [autoMode].
  */
 @Singleton
 class ProviderResolver @Inject constructor(
-    @ApplicationContext private val context: Context,
+    private val environment: ProviderEnvironment,
 ) {
 
-    /** The active provider, or `null` when no tasks provider is installed. */
-    fun resolve(): TaskProvider? {
-        for (candidate in CANDIDATES) {
-            val info = context.packageManager.resolveContentProvider(candidate.authority, 0)
-                ?: continue
-            return candidate.copy(packageName = info.packageName)
+    private val modeListeners = CopyOnWriteArrayList<() -> Unit>()
+
+    /**
+     * The user's explicit choice, or `null` while they have not made one (which is
+     * the normal state — most people never open Settings). Kept as a plain field
+     * rather than read from DataStore on demand because [resolve] is called from
+     * synchronous data-source code on every query, including from the main thread
+     * via `providerStatus()`. [StorageModeHolder] owns keeping it current.
+     *
+     * Assigning a *different* mode notifies [onModeChanged]: every live store
+     * observer is bound to one store and has to be moved across.
+     */
+    @Volatile
+    var storageMode: StorageMode? = null
+        set(value) {
+            val changed = field != value
+            field = value
+            if (changed) modeListeners.forEach { it() }
+        }
+
+    /**
+     * Observe switches between stores. Fires on the thread that set [storageMode]
+     * — [StorageModeHolder]'s collector — so listeners must be cheap and must not
+     * block.
+     */
+    fun onModeChanged(listener: () -> Unit): AutoCloseable {
+        modeListeners += listener
+        return AutoCloseable { modeListeners -= listener }
+    }
+
+    /** The active store, resolving the undecided case through [autoMode]. */
+    fun mode(): StorageMode = storageMode ?: autoMode()
+
+    /**
+     * The provider to query, or `null` — either because [StorageMode.OWN] is
+     * active and there is no provider involved at all, or because
+     * [StorageMode.EXTERNAL] is and none is installed. Callers that need to tell
+     * those apart ask [mode].
+     */
+    fun resolve(): TaskProvider? = when (mode()) {
+        StorageMode.OWN -> null
+        StorageMode.EXTERNAL -> resolveExternal()
+    }
+
+    /**
+     * What to use when the user has not chosen — and the one piece of real
+     * judgement in this class, because getting it wrong loses people their data.
+     *
+     * Ranking our own store first unconditionally would be wrong: someone who
+     * has been using Agendula over OpenTasks since 0.3.x would update, land on an
+     * empty database, and reasonably conclude their tasks were deleted.
+     *
+     * So the tell is **whether we already hold an external provider's runtime
+     * permission**. That is a dangerous permission — it can only be there because
+     * a previous version asked and the user agreed, which is precisely the
+     * definition of "this person is an existing Posture A user". A fresh install
+     * never holds it, and gets our own store.
+     *
+     * Deliberately cheap and synchronous: a PackageManager lookup and a permission
+     * check, no database probe. Settings overrides it either way.
+     */
+    fun autoMode(): StorageMode {
+        val external = resolveExternal()
+        return if (external != null && hasPermission(external)) StorageMode.EXTERNAL else StorageMode.OWN
+    }
+
+    /** The first installed external candidate, or `null` when none is present. */
+    fun resolveExternal(): TaskProvider? {
+        for (candidate in EXTERNAL_CANDIDATES) {
+            val packageName = environment.packageDeclaring(candidate.authority) ?: continue
+            return candidate.copy(packageName = packageName)
         }
         return null
     }
 
     fun hasPermission(provider: TaskProvider): Boolean =
-        granted(provider.readPermission) && granted(provider.writePermission)
+        environment.isGranted(provider.readPermission) && environment.isGranted(provider.writePermission)
 
-    private fun granted(permission: String): Boolean =
-        ContextCompat.checkSelfPermission(context, permission) == PackageManager.PERMISSION_GRANTED
+    /**
+     * Whether the active store can be read at all.
+     *
+     * [StorageMode.OWN] always can — it is our own database, with nothing to
+     * install and nothing to grant. Only [StorageMode.EXTERNAL] can be
+     * unreadable. Callers that gate on `resolve() != null` instead get this wrong
+     * the moment OWN is active, because OWN resolves to no provider by design.
+     */
+    fun canReadStore(): Boolean = when (mode()) {
+        StorageMode.OWN -> true
+        StorageMode.EXTERNAL -> resolveExternal()?.let(::hasPermission) == true
+    }
 
     companion object {
         /**
          * Verified on-device: tasks.org exposes `org.tasks.opentasks` backed by
-         * `org.dmfs.provider.tasks.TaskProvider`, guarded by
-         * `org.tasks.permission.*` (dangerous). OpenTasks uses `org.dmfs.tasks`
-         * + `org.dmfs.permission.*`. OpenTasks is listed first as the canonical
-         * authority; on a device with only one installed, order is moot.
+         * `org.dmfs.provider.tasks.TaskProvider`, guarded by `org.tasks.permission.*`
+         * (dangerous). OpenTasks uses `org.dmfs.tasks` + `org.dmfs.permission.*`.
+         * OpenTasks is listed first as the canonical authority; on a device with
+         * only one installed, order is moot.
          */
-        val CANDIDATES: List<TaskProvider> = listOf(
+        val EXTERNAL_CANDIDATES: List<TaskProvider> = listOf(
             TaskProvider(
                 authority = "org.dmfs.tasks",
                 readPermission = "org.dmfs.permission.READ_TASKS",

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/StartupGate.kt

@@ -0,0 +1,46 @@
+package de.jeanlucmakiola.agendula.data.tasks
+
+import de.jeanlucmakiola.agendula.data.di.ApplicationScope
+import de.jeanlucmakiola.agendula.data.tasks.legacy.OneShotImport
+import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.launch
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * The work that has to finish before anything reads a task store: the stored
+ * [StorageMode] has to reach [ProviderResolver], and a v0.3.x install's tasks
+ * have to be imported out of the dmfs provider's file into Room.
+ *
+ * Both are startup races with the same shape. Reading before the mode lands
+ * answers from `autoMode()` instead of the user's choice; reading before the
+ * import lands shows an upgrading user an empty app, which is the single worst
+ * thing this migration could do.
+ */
+@Singleton
+class StartupGate @Inject constructor(
+    private val storageModeHolder: StorageModeHolder,
+    private val oneShotImport: OneShotImport,
+    @ApplicationScope private val scope: CoroutineScope,
+) {
+
+    private val ready = CompletableDeferred<Unit>()
+
+    /** Call once, from `Application.onCreate`. */
+    fun start() {
+        storageModeHolder.start()
+        scope.launch {
+            // Opens the gate even on failure: a store that cannot be imported is
+            // still better shown empty than not shown at all, and the source file
+            // is left where it was either way.
+            runCatching {
+                storageModeHolder.awaitReady()
+                oneShotImport.runIfNeeded()
+            }
+            ready.complete(Unit)
+        }
+    }
+
+    suspend fun awaitReady() = ready.await()
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/StorageMode.kt

@@ -0,0 +1,26 @@
+package de.jeanlucmakiola.agendula.data.tasks
+
+/**
+ * Which task store backs the app — the user's choice, per `docs/OWN-STORE.md`.
+ *
+ * Only two values, though `docs/STORAGE-AND-SYNC.md` describes three modes.
+ * **Synced is not a third store**: it is [OWN] with an account attached to a
+ * list, which is derived state rather than something the user picks. Attaching
+ * one is a plain `UPDATE task_lists SET account_id = ?` — not the full data
+ * migration it was under the dmfs provider, whose `ACCOUNT_TYPE` was write-once.
+ */
+enum class StorageMode {
+    /**
+     * Agendula's own Room database. The default, and always available: there is
+     * no authority, no ContentResolver and no permission to grant.
+     */
+    OWN,
+
+    /**
+     * A tasks provider app already on the device (OpenTasks, tasks.org), synced by
+     * whatever that provider's engine is — DAVx5 and friends. Still fully
+     * supported, now a choice rather than the only way. Requires that provider's
+     * runtime read/write permissions.
+     */
+    EXTERNAL,
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/StorageModeHolder.kt

@@ -0,0 +1,47 @@
+package de.jeanlucmakiola.agendula.data.tasks
+
+import de.jeanlucmakiola.agendula.data.di.ApplicationScope
+import de.jeanlucmakiola.agendula.data.prefs.SettingsPrefs
+import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.launch
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Mirrors the stored [StorageMode] into [ProviderResolver].
+ *
+ * The resolver is consulted synchronously from every data-source call and from
+ * `providerStatus()` on the main thread, so it cannot read DataStore itself.
+ * This is the one component that bridges the two: it collects the preference for
+ * the life of the process and pushes each value across.
+ *
+ * [awaitReady] exists for the startup race. Until the first DataStore emission
+ * arrives the resolver's mode is `null` and `ProviderResolver.autoMode` answers
+ * instead — fine as a steady state, wrong for a user who explicitly chose the
+ * other mode. Anything that touches the provider before the UI is up (the launch
+ * reminder re-sync, notably) should wait rather than risk reading the wrong
+ * store and rescheduling every alarm off it.
+ */
+@Singleton
+class StorageModeHolder @Inject constructor(
+    private val prefs: SettingsPrefs,
+    private val resolver: ProviderResolver,
+    @ApplicationScope private val scope: CoroutineScope,
+) {
+
+    private val firstValue = CompletableDeferred<Unit>()
+
+    /** Starts mirroring. Idempotent in effect; call once, from `Application.onCreate`. */
+    fun start() {
+        scope.launch {
+            prefs.storageMode.collect { mode ->
+                resolver.storageMode = mode
+                firstValue.complete(Unit)
+            }
+        }
+    }
+
+    /** Suspends until the stored mode has been applied at least once. */
+    suspend fun awaitReady() = firstValue.await()
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/TaskMapper.kt

@@ -5,6 +5,7 @@ import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Lists
 import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Tasks
 import de.jeanlucmakiola.agendula.domain.Task
 import de.jeanlucmakiola.agendula.domain.TaskList
+import de.jeanlucmakiola.agendula.domain.export.ExportTask
 import de.jeanlucmakiola.agendula.domain.priorityFromICal
 import de.jeanlucmakiola.agendula.domain.statusFromInt
 import kotlin.time.Instant
@@ -16,10 +17,17 @@ object TaskMapper {
         fun instant(name: String): Instant? =
             r.getLong(name)?.let { Instant.fromEpochMilliseconds(it) }
 
-        val instanceId = r.getLong(Tasks.ID) ?: 0L
+        val rowId = r.getLong(Tasks.ID) ?: 0L
+        // Derived from the rule columns rather than the `is_recurring` column
+        // alone: that column only exists from OpenTasks 1.4.0 (DB 23) and is
+        // absent on tasks.org's bundled provider (DB 22), where reading it
+        // would silently report every recurring task as one-off — and route
+        // its edits onto the series anchor.
+        val recurring = r.getString(Tasks.RRULE) != null ||
+            r.getString(Tasks.RDATE) != null ||
+            r.getBoolean(Instances.IS_RECURRING)
         return Task(
-            id = instanceId,
-            taskId = r.getLong(Instances.TASK_ID) ?: instanceId,
+            taskId = r.getLong(Instances.TASK_ID) ?: rowId,
             listId = r.getLong(Tasks.LIST_ID) ?: 0L,
             title = r.getString(Tasks.TITLE).orEmpty(),
             description = r.getString(Tasks.DESCRIPTION),
@@ -38,13 +46,66 @@ object TaskMapper {
             listName = r.getString(Tasks.LIST_NAME),
             accountName = r.getString(Tasks.ACCOUNT_NAME),
             parentId = r.getLong(Tasks.PARENT_ID),
-            isRecurring = r.getBoolean(Instances.IS_RECURRING),
+            isRecurring = recurring,
+            occurrenceStart = if (recurring) occurrenceAnchor(r) else null,
             distanceFromCurrent = r.getInt(Instances.DISTANCE_FROM_CURRENT),
             created = instant(Tasks.CREATED),
             lastModified = instant(Tasks.LAST_MODIFIED),
         )
     }
 
+    /**
+     * The occurrence's `RECURRENCE-ID` anchor.
+     *
+     * `instance_original_time` is the provider's own name for it and is set on
+     * every occurrence of a recurring task, so it is read first. It is absent on
+     * older provider schemas, where the fallbacks reconstruct the same value: a
+     * DTSTART-anchored series instantiates each occurrence at its start, and a
+     * series carrying only DUE anchors on the due date instead.
+     */
+    fun occurrenceAnchor(r: ColumnReader): Instant? =
+        (
+            r.getLong(Instances.INSTANCE_ORIGINAL_TIME)
+                ?: r.getLong(Instances.INSTANCE_START)
+                ?: r.getLong(Instances.INSTANCE_DUE)
+            )?.let { Instant.fromEpochMilliseconds(it) }
+
+    /**
+     * Maps a row of the **`tasks` table** — a master task, not an occurrence.
+     *
+     * Export reads there rather than from `instances` on purpose: in the instances
+     * view a recurring task appears once per occurrence with its times already
+     * resolved and no rule attached, so exporting from it would write the same
+     * task many times over and drop the RRULE that produced them. Here each task
+     * appears exactly once, carrying the rule itself.
+     */
+    fun exportTask(r: ColumnReader): ExportTask {
+        fun instant(name: String): Instant? =
+            r.getLong(name)?.let { Instant.fromEpochMilliseconds(it) }
+
+        return ExportTask(
+            taskId = r.getLong(Tasks.ID) ?: 0L,
+            uid = r.getString(Tasks.UID),
+            title = r.getString(Tasks.TITLE).orEmpty(),
+            description = r.getString(Tasks.DESCRIPTION),
+            location = r.getString(Tasks.LOCATION),
+            url = r.getString(Tasks.URL),
+            priority = priorityFromICal(r.getInt(Tasks.PRIORITY)),
+            status = statusFromInt(r.getInt(Tasks.STATUS)),
+            percentComplete = r.getInt(Tasks.PERCENT_COMPLETE),
+            // The task's own columns, not the instance view's resolved ones.
+            start = instant(Tasks.DTSTART),
+            due = instant(Tasks.DUE),
+            isAllDay = r.getBoolean(Tasks.IS_ALLDAY),
+            completedAt = instant(Tasks.COMPLETED),
+            created = instant(Tasks.CREATED),
+            lastModified = instant(Tasks.LAST_MODIFIED),
+            rrule = r.getString(Tasks.RRULE),
+            rdate = r.getString(Tasks.RDATE),
+            parentId = r.getLong(Tasks.PARENT_ID)?.takeIf { it > 0 },
+        )
+    }
+
     fun taskList(r: ColumnReader): TaskList = TaskList(
         id = r.getLong(Lists.ID) ?: 0L,
         name = r.getString(Lists.NAME).orEmpty(),

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/TaskProjections.kt

@@ -1,8 +1,6 @@
 package de.jeanlucmakiola.agendula.data.tasks
 
-import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Instances
 import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Lists
-import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Tasks
 
 /** Column lists requested from the provider. Order is irrelevant; we read by name. */
 object TaskProjections {
@@ -18,31 +16,9 @@ object TaskProjections {
         Lists.ACCOUNT_TYPE,
     )
 
-    /** Read from the `instances` view (inherits all task columns). */
-    val INSTANCES: Array<String> = arrayOf(
-        Tasks.ID,
-        Instances.TASK_ID,
-        Tasks.LIST_ID,
-        Tasks.TITLE,
-        Tasks.DESCRIPTION,
-        Tasks.LOCATION,
-        Tasks.URL,
-        Tasks.PRIORITY,
-        Tasks.STATUS,
-        Tasks.PERCENT_COMPLETE,
-        Tasks.COMPLETED,
-        Tasks.IS_ALLDAY,
-        Tasks.TZ,
-        Instances.INSTANCE_START,
-        Instances.INSTANCE_DUE,
-        Tasks.TASK_COLOR,
-        Tasks.LIST_COLOR,
-        Tasks.LIST_NAME,
-        Tasks.ACCOUNT_NAME,
-        Tasks.PARENT_ID,
-        Instances.IS_RECURRING,
-        Instances.DISTANCE_FROM_CURRENT,
-        Tasks.CREATED,
-        Tasks.LAST_MODIFIED,
-    )
+    // No `instances` projection on purpose: that read passes `projection = null`
+    // (all columns), because the view's shape differs across provider versions —
+    // tasks.org's bundled OpenTasks has no `is_recurring`, for one. A fixed list
+    // here would drift out of sync with the by-name mapper and quietly drop
+    // columns it depends on. See AndroidTasksDataSource.queryInstances.
 }

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/TaskWriteMapper.kt

@@ -1,9 +1,21 @@
 package de.jeanlucmakiola.agendula.data.tasks
 
+import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Alarm
 import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Lists
+import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Properties
 import de.jeanlucmakiola.agendula.data.tasks.TasksContract.Tasks
 import de.jeanlucmakiola.agendula.domain.TaskForm
 import de.jeanlucmakiola.agendula.domain.toICal
+import kotlin.time.Instant
+
+private const val MILLIS_PER_DAY = 24L * 60 * 60 * 1000
+
+/** Floor to UTC midnight when [allDay], else pass through unchanged. */
+private fun Instant.forAllDay(allDay: Boolean): Instant =
+    if (!allDay) this
+    else Instant.fromEpochMilliseconds(
+        Math.floorDiv(toEpochMilliseconds(), MILLIS_PER_DAY) * MILLIS_PER_DAY,
+    )
 
 /**
  * Turns a [TaskForm] / mutation into a name→value map. Pure (no ContentValues),
@@ -39,8 +51,17 @@ object TaskWriteMapper {
             }
         }
         put(Tasks.IS_ALLDAY, if (form.isAllDay) 1 else 0)
-        put(Tasks.DTSTART, form.start?.toEpochMilliseconds())
-        put(Tasks.DUE, form.due?.toEpochMilliseconds())
+        // All-day tasks are date-only in iCalendar. The provider reads them back
+        // through DateTime.toAllDay(), which drops the time-of-day and resolves the
+        // remaining date against UTC — so a local-midnight instant lands on the
+        // previous day for anyone west of UTC. Pin all-day values to UTC midnight.
+        put(Tasks.DTSTART, form.start?.forAllDay(form.isAllDay)?.toEpochMilliseconds())
+        put(Tasks.DUE, form.due?.forAllDay(form.isAllDay)?.toEpochMilliseconds())
+        // DUE and DURATION are mutually exclusive. The provider's Validating
+        // processor evaluates the *merged* row (supplied values over the stored
+        // ones), so writing DUE onto a task that already carries a DURATION throws
+        // "Only one of DUE or DURATION must be supplied." Clear it alongside.
+        put(Tasks.DURATION, null)
         put(Tasks.PARENT_ID, form.parentId)
         // The provider treats a null tz as local time; set it explicitly for
         // timed tasks so the stored instant is unambiguous across zones.
@@ -48,6 +69,16 @@ object TaskWriteMapper {
         put(Tasks.TZ, if (timed) tzId else null)
     }
 
+    /**
+     * Values for an update through the *instances* URI (a recurring occurrence).
+     * The provider clones the row into an override and strips list/recurrence
+     * fields as it goes, so LIST_ID and PARENT_ID are dropped here rather than
+     * written and silently ignored — moving one occurrence between lists or
+     * parents isn't a thing the override model expresses.
+     */
+    fun instanceValues(form: TaskForm, tzId: String): Map<String, Any?> =
+        taskValues(form, tzId) - Tasks.LIST_ID - Tasks.PARENT_ID
+
     fun completionValues(completed: Boolean, nowMillis: Long): Map<String, Any?> =
         if (completed) {
             mapOf(
@@ -63,9 +94,26 @@ object TaskWriteMapper {
             )
         }
 
-    fun localListValues(name: String, color: Int): Map<String, Any?> = mapOf(
+    /**
+     * A reminder for [taskId], as an Alarm property row. The provider's validator
+     * requires MINUTES_BEFORE, REFERENCE (non-negative) and ALARM_TYPE on every
+     * write, so all three are always present.
+     */
+    fun alarmValues(taskId: Long, minutesBeforeDue: Int): Map<String, Any?> = mapOf(
+        Properties.TASK_ID to taskId,
+        Properties.MIMETYPE to Alarm.MIMETYPE,
+        Alarm.MINUTES_BEFORE to minutesBeforeDue,
+        Alarm.REFERENCE to Alarm.REFERENCE_DUE,
+        Alarm.ALARM_TYPE to Alarm.TYPE_MESSAGE,
+    )
+
+    /** The user-owned columns of a list — what an edit is allowed to change. */
+    fun listValues(name: String, color: Int): Map<String, Any?> = mapOf(
         Lists.NAME to name.trim(),
         Lists.COLOR to color,
+    )
+
+    fun localListValues(name: String, color: Int): Map<String, Any?> = listValues(name, color) + mapOf(
         Lists.ACCOUNT_NAME to TasksContract.LOCAL_ACCOUNT_NAME,
         Lists.ACCOUNT_TYPE to TasksContract.LOCAL_ACCOUNT_TYPE,
         Lists.VISIBLE to 1,

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/TasksContract.kt

@@ -66,6 +66,9 @@ object TasksContract {
         const val IS_ALLDAY = "is_allday"
         const val TZ = "tz"
         const val RRULE = "rrule"
+        const val RDATE = "rdate"
+        /** Set on an override row — the master occurrence this one replaces. */
+        const val ORIGINAL_INSTANCE_ID = "original_instance_id"
         const val PARENT_ID = "parent_id"
         const val SORTING = "sorting"
         const val CREATED = "created"
@@ -96,8 +99,59 @@ object TasksContract {
         const val INSTANCE_DUE_SORTING = "instance_due_sorting"
         const val DISTANCE_FROM_CURRENT = "distance_from_current"
         const val IS_RECURRING = "is_recurring"
+
+        /**
+         * The occurrence's `RECURRENCE-ID` — the time this occurrence was
+         * instantiated at, before any override moved it. Set on every occurrence
+         * of a recurring task, which is what makes it the occurrence's identity.
+         */
+        const val INSTANCE_ORIGINAL_TIME = "instance_original_time"
     }
 
+    /** The `properties` table — per-task side rows, discriminated by [Properties.MIMETYPE]. */
+    object Properties {
+        const val PATH = "properties"
+        const val PROPERTY_ID = "property_id"
+        const val TASK_ID = "task_id"
+        const val MIMETYPE = "mimetype"
+    }
+
+    /**
+     * An alarm property row — a per-task reminder lead.
+     *
+     * Storage and sync format *only*: the provider fires nothing (its alarm
+     * scheduling is commented out and the internal `alarms` table is never
+     * populated), so [de.jeanlucmakiola.agendula.data.reminders.ReminderScheduler]
+     * still arms the real AlarmManager alarm. Writing it here is what makes the
+     * lead survive a sync and show up in other OpenTasks clients.
+     *
+     * The columns are the generic `dataN` slots; the meanings below are the
+     * Alarm property's contract for them.
+     */
+    object Alarm {
+        const val MIMETYPE = "vnd.android.cursor.item/alarm"
+
+        /** `data0` — minutes from the reference date; positive means *before* it. */
+        const val MINUTES_BEFORE = "data0"
+
+        /** `data1` — which date to count from. */
+        const val REFERENCE = "data1"
+
+        /** `data2` — optional message shown with the alarm. */
+        const val MESSAGE = "data2"
+
+        /** `data3` — alarm kind. Must be present, and non-zero to count as an alarm. */
+        const val ALARM_TYPE = "data3"
+
+        const val REFERENCE_DUE = 1
+        const val REFERENCE_START = 2
+
+        /** 0 (NOTHING) is excluded from the provider's `has_alarms` count — use MESSAGE. */
+        const val TYPE_MESSAGE = 1
+    }
+
+    fun propertiesUri(authority: String): Uri = Uri.parse("content://$authority/${Properties.PATH}")
+
     // --- status values (TaskColumns.STATUS_*) --------------------------------
     const val STATUS_NEEDS_ACTION = 0
     const val STATUS_IN_PROCESS = 1
@@ -109,9 +163,20 @@ object TasksContract {
 
     fun authorityUri(authority: String): Uri = Uri.parse("content://$authority")
     fun listsUri(authority: String): Uri = Uri.parse("content://$authority/${Lists.PATH}")
+    fun listUri(authority: String, listId: Long): Uri =
+        Uri.parse("content://$authority/${Lists.PATH}/$listId")
     fun tasksUri(authority: String): Uri = Uri.parse("content://$authority/${Tasks.PATH}")
     fun instancesUri(authority: String): Uri = Uri.parse("content://$authority/${Instances.PATH}")
 
+    /**
+     * A single occurrence. Updating through this URI is how a *recurring* task is
+     * edited: the provider clones the row into an override task
+     * (`original_instance_id` set, recurrence fields stripped) instead of moving
+     * the series anchor, which is what writing to `tasks/<id>` would do.
+     */
+    fun instanceUri(authority: String, instanceId: Long): Uri =
+        Uri.parse("content://$authority/${Instances.PATH}/$instanceId")
+
     /** Append the sync-adapter params required to write local-account rows. */
     fun asSyncAdapter(uri: Uri, accountName: String, accountType: String): Uri =
         uri.buildUpon()

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/TasksDataSource.kt

@@ -3,6 +3,17 @@ package de.jeanlucmakiola.agendula.data.tasks
 import de.jeanlucmakiola.agendula.domain.Task
 import de.jeanlucmakiola.agendula.domain.TaskForm
 import de.jeanlucmakiola.agendula.domain.TaskList
+import kotlin.time.Instant
+
+/**
+ * A stored reminder: how long before, and what it counts back from.
+ *
+ * [fromStart] matters because both stores can hold a `START`-referenced alarm —
+ * the dmfs import preserves one, and an external provider's other clients write
+ * them — while Agendula's own UI only ever sets a before-due lead. Collapsing it
+ * to a number here is what silently fired those reminders off the wrong anchor.
+ */
+data class TaskReminder(val minutesBefore: Int, val fromStart: Boolean = false)
 
 /** What to fetch from the provider. Smart-list date logic is applied above this. */
 data class TaskQuery(
@@ -23,10 +34,67 @@ interface TasksDataSource {
 
     fun insertTask(form: TaskForm): Long
     fun updateTask(taskId: Long, form: TaskForm)
+
+    /**
+     * Update a single occurrence of a recurring task, addressed by the task row and
+     * the occurrence's `RECURRENCE-ID` anchor ([Task.occurrenceStart]). The store
+     * forks an override rather than moving the series anchor — which is what
+     * [updateTask] would do, since a recurring task's start/due are the
+     * occurrence's resolved times.
+     *
+     * Addressing by `(taskId, occurrenceStart)` rather than by a materialised
+     * instance row id keeps this seam independent of any one store's row
+     * numbering; External mode maps it back to an instance row itself.
+     */
+    fun updateInstance(taskId: Long, occurrenceStart: Instant, form: TaskForm)
+    /**
+     * Set (or clear, with `null`) the per-task reminder lead, stored as an Alarm
+     * property row. The provider never fires it — [de.jeanlucmakiola.agendula
+     * .data.reminders.ReminderScheduler] does — but persisting it here is what
+     * syncs the lead and shares it with other OpenTasks clients.
+     */
+    fun setAlarm(taskId: Long, minutesBeforeDue: Int?)
+
+    /** Every task's reminder, by task id. One query, for the scheduler. */
+    fun alarms(): Map<Long, TaskReminder>
+
+    /**
+     * Every task in [listId] read from the **`tasks` table**, for export. Masters,
+     * not occurrences — see [TaskMapper.exportTask] for why that distinction
+     * matters. Excludes rows the provider has flagged deleted-but-unsynced.
+     */
+    fun exportTasks(listId: Long): List<de.jeanlucmakiola.agendula.domain.export.ExportTask>
+
     fun setCompleted(taskId: Long, completed: Boolean)
+
+    /**
+     * Complete (or reopen) **one occurrence** of a recurring task, addressed the
+     * same way [updateInstance] is. Ticking a series through [setCompleted] would
+     * close the master row, which takes every past and future occurrence out of
+     * every list at once.
+     *
+     * Implementations fall back to [setCompleted] when the row turns out not to
+     * be a series master — an override, or a plain task the caller happened to
+     * hand an anchor for — so the routing above cannot get this wrong.
+     */
+    fun setCompletedInstance(taskId: Long, occurrenceStart: Instant, completed: Boolean)
     fun deleteTask(taskId: Long)
     fun createLocalList(name: String, color: Int): Long
 
+    /** Rename and recolour [listId]. */
+    fun updateList(listId: Long, name: String, color: Int)
+
+    /**
+     * Delete [listId] **and the tasks in it** — `tasks.list_id` cascades on the
+     * Room path, and the provider does the same on the External one.
+     *
+     * Only ever called for a local, device-only list: a collection that belongs
+     * to an account is the server's to remove, and neither store expresses a
+     * collection tombstone yet. The UI gates on [TaskList.isLocal]; this seam
+     * does not re-check it.
+     */
+    fun deleteList(listId: Long)
+
     /** Observe any change to tasks/lists; [onChange] fires on a background thread. */
     fun registerObserver(onChange: () -> Unit): AutoCloseable
 }

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/TasksRepository.kt

@@ -37,9 +37,25 @@ interface TasksRepository {
      * since the form loaded. Pass `null` to force the write (overwrite-anyway).
      */
     suspend fun updateTask(taskId: Long, form: TaskForm, expectedLastModified: Instant? = null)
-    suspend fun setCompleted(taskId: Long, completed: Boolean)
+    /**
+     * Complete or reopen a task. Pass the occurrence's [Task.occurrenceStart] so a
+     * recurring series forks a `RECURRENCE-ID` override for that one occurrence
+     * instead of closing the whole series; `null` completes the row itself.
+     */
+    suspend fun setCompleted(taskId: Long, occurrenceStart: Instant?, completed: Boolean)
     suspend fun deleteTask(taskId: Long)
+
+    /**
+     * The per-task reminder lead in minutes before due, or `null` if the task has
+     * none (in which case the list's / global setting applies). Read when the edit
+     * form loads so saving can't silently drop it.
+     */
+    suspend fun reminderFor(taskId: Long): Int?
     suspend fun createLocalList(name: String, color: Int): Long
+    suspend fun updateList(listId: Long, name: String, color: Int)
+
+    /** Deletes the list **and its tasks**. Local lists only — see [TasksDataSource.deleteList]. */
+    suspend fun deleteList(listId: Long)
 
     /** Synchronous snapshot for the permission/onboarding gate. */
     fun providerStatus(): ProviderStatus

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/TasksRepositoryImpl.kt

@@ -28,6 +28,7 @@ import kotlin.time.Instant
 class TasksRepositoryImpl @Inject constructor(
     private val dataSource: TasksDataSource,
     private val providerResolver: ProviderResolver,
+    private val startupGate: StartupGate,
     @IoDispatcher private val io: CoroutineDispatcher,
 ) : TasksRepository {
 
@@ -80,22 +81,50 @@ class TasksRepositoryImpl @Inject constructor(
     }
 
     override suspend fun createTask(form: TaskForm): Long =
-        withContext(io) { dataSource.insertTask(form) }
+        withContext(io) {
+            val id = dataSource.insertTask(form)
+            form.reminderMinutesBeforeDue?.let { dataSource.setAlarm(id, it) }
+            id
+        }
+
+    override suspend fun reminderFor(taskId: Long): Int? =
+        withContext(io) { runCatching { dataSource.alarms()[taskId]?.minutesBefore }.getOrNull() }
 
     override suspend fun updateTask(taskId: Long, form: TaskForm, expectedLastModified: Instant?) =
         withContext(io) {
-            // Conflict-safe overwrite: re-read just before writing and bail if the
-            // provider's last_modified moved since the form captured it (external
-            // sync / another app). A null baseline means "force / overwrite anyway".
+            // Re-read just before writing: it settles the conflict check *and* tells
+            // us which URI to write through.
+            val current = dataSource.task(taskId)
+            // Conflict-safe overwrite: bail if the provider's last_modified moved
+            // since the form captured it (external sync / another app). A null
+            // baseline means "force / overwrite anyway".
             if (expectedLastModified != null) {
-                val current = dataSource.task(taskId)?.lastModified
-                if (current != null && current != expectedLastModified) throw TaskConflictException(taskId)
+                val seen = current?.lastModified
+                if (seen != null && seen != expectedLastModified) throw TaskConflictException(taskId)
+            }
+            // Write the reminder first: forking a recurring occurrence copies the
+            // task's properties onto the new override row, so setting the alarm
+            // beforehand is what carries it across.
+            dataSource.setAlarm(taskId, form.reminderMinutesBeforeDue)
+            // A recurring task's start/due are one occurrence's resolved times, so
+            // writing them back to the task row would re-anchor the whole series.
+            // Going through the occurrence forks an override instead.
+            val occurrence = current?.takeIf { it.isRecurring }?.occurrenceStart
+            if (occurrence != null) {
+                dataSource.updateInstance(taskId, occurrence, form)
+            } else {
+                dataSource.updateTask(taskId, form)
             }
-            dataSource.updateTask(taskId, form)
         }
 
-    override suspend fun setCompleted(taskId: Long, completed: Boolean) =
-        withContext(io) { dataSource.setCompleted(taskId, completed) }
+    override suspend fun setCompleted(taskId: Long, occurrenceStart: Instant?, completed: Boolean) =
+        withContext(io) {
+            if (occurrenceStart != null) {
+                dataSource.setCompletedInstance(taskId, occurrenceStart, completed)
+            } else {
+                dataSource.setCompleted(taskId, completed)
+            }
+        }
 
     override suspend fun deleteTask(taskId: Long) =
         withContext(io) { dataSource.deleteTask(taskId) }
@@ -103,18 +132,32 @@ class TasksRepositoryImpl @Inject constructor(
     override suspend fun createLocalList(name: String, color: Int): Long =
         withContext(io) { dataSource.createLocalList(name, color) }
 
+    override suspend fun updateList(listId: Long, name: String, color: Int) =
+        withContext(io) { dataSource.updateList(listId, name, color) }
+
+    override suspend fun deleteList(listId: Long) =
+        withContext(io) { dataSource.deleteList(listId) }
+
     override fun providerStatus(): ProviderStatus {
+        // Our own store is always ready: it ships with the app, needs no provider
+        // and no grant. The permission gate only ever applied to External mode —
+        // now that is visibly true rather than a special case inside it.
+        if (providerResolver.mode() == StorageMode.OWN) return ProviderStatus.READY
         val provider = providerResolver.resolve() ?: return ProviderStatus.NO_PROVIDER
         return if (providerResolver.hasPermission(provider)) ProviderStatus.READY
         else ProviderStatus.NEEDS_PERMISSION
     }
 
     /**
-     * Emits an initial load, then re-loads on every provider change. The observer
+     * Emits an initial load, then re-loads on every store change. The observer
      * callback (main thread) only pokes a conflated channel; the actual blocking
      * query runs on [io].
      */
     private fun <T> observing(load: () -> T): Flow<T> = callbackFlow {
+        // Nothing reads a store before the stored mode has landed and a v0.3.x
+        // install has been imported — otherwise the first emission comes from the
+        // wrong store, or from an empty one.
+        startupGate.awaitReady()
         val ticks = Channel<Unit>(Channel.CONFLATED)
         val handle = dataSource.registerObserver { ticks.trySend(Unit) }
         ticks.trySend(Unit) // prime the initial emission

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/legacy/OneShotImport.kt

@@ -0,0 +1,384 @@
+package de.jeanlucmakiola.agendula.data.tasks.legacy
+
+import android.content.Context
+import android.database.sqlite.SQLiteDatabase
+import androidx.datastore.core.DataStore
+import androidx.datastore.preferences.core.Preferences
+import androidx.datastore.preferences.core.booleanPreferencesKey
+import androidx.datastore.preferences.core.edit
+import dagger.hilt.android.qualifiers.ApplicationContext
+import de.jeanlucmakiola.agendula.data.tasks.CursorColumnReader
+import de.jeanlucmakiola.agendula.data.tasks.room.AlarmReference
+import de.jeanlucmakiola.agendula.data.tasks.room.TaskAlarmEntity
+import de.jeanlucmakiola.agendula.data.tasks.room.TaskEntity
+import de.jeanlucmakiola.agendula.data.tasks.room.TaskListEntity
+import de.jeanlucmakiola.agendula.data.tasks.room.TasksDatabase
+import de.jeanlucmakiola.agendula.domain.PRIORITY_NONE
+import de.jeanlucmakiola.agendula.domain.statusFromInt
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.withContext
+import java.io.File
+import java.util.UUID
+import javax.inject.Inject
+import javax.inject.Singleton
+import kotlin.time.Instant
+
+/** How much one import moved. */
+data class ImportCounts(val lists: Int, val tasks: Int, val alarms: Int)
+
+/** The outcome of [OneShotImport.runIfNeeded] or [OneShotImport.reimportFromArchive]. */
+sealed interface ImportResult {
+    /** The DataStore flag was already set; nothing was read. */
+    data object AlreadyDone : ImportResult
+
+    /** No legacy database on disk — a fresh install, or one already archived. */
+    data object NothingToImport : ImportResult
+
+    data class Imported(val counts: ImportCounts) : ImportResult
+
+    /** Nothing landed: the transaction rolled back and the source is untouched. */
+    data class Failed(val cause: Throwable) : ImportResult
+}
+
+/**
+ * Moves a v0.3.x install's tasks out of the bundled dmfs provider's SQLite file
+ * and into Room, once (`docs/OWN-STORE.md`, "Migrating existing users").
+ *
+ * The file is opened read-only and directly — no provider, no ContentResolver —
+ * so this keeps working after `:provider` is deleted. Everything lands in one
+ * Room transaction with verified counts, so a failure leaves Room exactly as it
+ * was and the source file exactly where it was.
+ *
+ * dmfs accounts are not carried over: every list is imported as a device-only
+ * list (`account_id IS NULL`), including one that sat under a real account —
+ * only reachable if the user had pointed DAVx5 at our authority. Their task
+ * `uid`s are preserved, which is what lets those rows be re-attached to an
+ * account once sync lands.
+ */
+@Singleton
+class OneShotImport @Inject constructor(
+    @ApplicationContext private val context: Context,
+    private val database: TasksDatabase,
+    private val dataStore: DataStore<Preferences>,
+) {
+
+    /** Whether the import has run. Set before the rename, so both guards hold. */
+    val isDone: Flow<Boolean> = dataStore.data.map { it[IMPORT_DONE] ?: false }
+
+    /**
+     * Steps 1–8 of the plan: archive `databases/tasks.db`, import it, record
+     * completion. Safe to call on every launch.
+     *
+     * The archive happens *before* the import, and the import always replaces, so
+     * that every point this can be killed at re-enters correctly:
+     *
+     * - killed after the rename, before the import — the next run finds the
+     *   archive, imports it, and nothing is lost;
+     * - killed after the import commits, before the flag is written — the next
+     *   run truncates and re-imports the same archive, so the result is the same
+     *   rather than doubled.
+     *
+     * Renaming last would leave that second window open: the flag would be unset
+     * and `tasks.db` still in place, and the next launch would import it a second
+     * time on top of the first. That is the window the plan's "guarded by a
+     * DataStore flag *and* by the rename" is meant to close, and only this order
+     * actually closes it.
+     */
+    suspend fun runIfNeeded(): ImportResult = withContext(Dispatchers.IO) {
+        if (isDone.first()) return@withContext ImportResult.AlreadyDone
+        val source = archivedSource() ?: run {
+            markDone()
+            return@withContext ImportResult.NothingToImport
+        }
+        val counts = runCatching { importFrom(source, replaceExisting = true) }
+            .getOrElse { return@withContext ImportResult.Failed(it) }
+        markDone()
+        ImportResult.Imported(counts)
+    }
+
+    /**
+     * The rollback path: re-run against the archived `tasks.db.imported`,
+     * truncating the Room tables first so a second attempt replaces rather than
+     * merges. Reached by a targeted fix release, not by the app on its own.
+     */
+    suspend fun reimportFromArchive(): ImportResult = withContext(Dispatchers.IO) {
+        val source = archivedSource() ?: return@withContext ImportResult.NothingToImport
+        val counts = runCatching { importFrom(source, replaceExisting = true) }
+            .getOrElse { return@withContext ImportResult.Failed(it) }
+        markDone()
+        ImportResult.Imported(counts)
+    }
+
+    /**
+     * The legacy database as `tasks.db.imported`, archiving it first if it is
+     * still under its live name. `null` when there is nothing to import.
+     */
+    private fun archivedSource(): File? {
+        val archive = context.getDatabasePath(ARCHIVE_NAME)
+        if (archive.exists()) return archive
+        val live = context.getDatabasePath(LEGACY_NAME)
+        if (!live.exists()) return null
+        return if (archive(live)) archive else live
+    }
+
+    /** Clears the completion flag so [runIfNeeded] will import again. */
+    suspend fun clearCompletion() {
+        dataStore.edit { it.remove(IMPORT_DONE) }
+    }
+
+    /**
+     * Steps 2–6 against an arbitrary dmfs database: read it read-only, then write
+     * everything in one Room transaction whose counts are verified before it
+     * commits. Blocking — call it off the main thread.
+     */
+    fun importFrom(source: File, replaceExisting: Boolean = false): ImportCounts {
+        val snapshot = SQLiteDatabase.openDatabase(source.path, null, SQLiteDatabase.OPEN_READONLY)
+            .use(::read)
+        return database.runInTransaction<ImportCounts> {
+            if (replaceExisting) truncate()
+            val baseline = tableCounts()
+            val written = write(snapshot)
+            verify(written, baseline)
+            written
+        }
+    }
+
+    // --- reading the dmfs file ------------------------------------------------
+
+    private fun read(db: SQLiteDatabase): LegacySnapshot {
+        val lists = mutableListOf<LegacyList>()
+        db.rawQuery("SELECT * FROM Lists ORDER BY _id", null).use { cursor ->
+            val r = CursorColumnReader(cursor)
+            while (cursor.moveToNext()) {
+                val id = r.getLong("_id") ?: continue
+                lists += LegacyList(
+                    id = id,
+                    entity = TaskListEntity(
+                        name = r.getString("list_name").orEmpty(),
+                        color = r.getInt("list_color") ?: 0,
+                        accountId = null,
+                        isVisible = r.getBoolean("visible"),
+                        isSynced = r.getBoolean("sync_enabled"),
+                        owner = r.getString("list_owner"),
+                    ),
+                )
+            }
+        }
+
+        val rows = mutableListOf<LegacyTaskRow>()
+        db.rawQuery("SELECT * FROM Tasks WHERE _deleted IS NULL OR _deleted = 0 ORDER BY _id", null)
+            .use { cursor ->
+                val r = CursorColumnReader(cursor)
+                while (cursor.moveToNext()) {
+                    val id = r.getLong("_id") ?: continue
+                    rows += LegacyTaskRow(
+                        id = id,
+                        listId = r.getLong("list_id") ?: continue,
+                        parentId = r.getLong("parent_id"),
+                        masterId = r.getLong("original_instance_id"),
+                        recurrenceId = r.instant("original_instance_time"),
+                        entity = TaskEntity(
+                            listId = 0,
+                            uid = r.getString("_uid") ?: UUID.randomUUID().toString(),
+                            title = r.getString("title"),
+                            description = r.getString("description"),
+                            location = r.getString("location"),
+                            url = r.getString("url"),
+                            color = r.getInt("task_color"),
+                            status = statusFromInt(r.getInt("status")),
+                            percentComplete = r.getInt("percent_complete"),
+                            completedAt = r.instant("completed"),
+                            priority = r.getInt("priority") ?: PRIORITY_NONE,
+                            classification = r.getInt("class"),
+                            dtstart = r.instant("dtstart"),
+                            due = r.instant("due"),
+                            duration = r.getString("duration"),
+                            isAllDay = r.getBoolean("is_allday"),
+                            timezone = r.getString("tz"),
+                            rrule = r.getString("rrule"),
+                            rdate = r.getString("rdate"),
+                            exdate = r.getString("exdate"),
+                            createdAt = r.instant("created"),
+                            lastModified = r.instant("last_modified"),
+                        ),
+                    )
+                }
+            }
+
+        val alarms = mutableListOf<LegacyAlarm>()
+        db.rawQuery("SELECT task_id, mimetype, data0, data1, data2 FROM Properties", null)
+            .use { cursor ->
+                val r = CursorColumnReader(cursor)
+                while (cursor.moveToNext()) {
+                    if (r.getString("mimetype") != ALARM_MIMETYPE) continue
+                    val taskId = r.getLong("task_id") ?: continue
+                    val minutes = r.getString("data0")?.trim()?.toIntOrNull() ?: continue
+                    alarms += LegacyAlarm(
+                        taskId = taskId,
+                        minutesBefore = minutes,
+                        reference = if (r.getString("data1")?.trim() == REFERENCE_START) {
+                            AlarmReference.START
+                        } else {
+                            AlarmReference.DUE
+                        },
+                        message = r.getString("data2"),
+                    )
+                }
+            }
+
+        return LegacySnapshot(lists, rows, alarms)
+    }
+
+    // --- writing into Room ----------------------------------------------------
+
+    /**
+     * dmfs `list_id`, `parent_id` and `original_instance_id` are old row ids, and
+     * Room mints its own on insert, so every one of them is remapped through the
+     * ids the inserts hand back. Tasks are inserted with their links cleared and
+     * a second pass sets them, because a parent may be a higher `_id` than its
+     * child.
+     */
+    private fun write(snapshot: LegacySnapshot): ImportCounts {
+        val listDao = database.taskLists()
+        val taskDao = database.tasks()
+        val alarmDao = database.alarms()
+
+        val listIds = snapshot.lists.associate { it.id to listDao.insert(it.entity) }
+
+        // A task whose list is missing is already invisible in dmfs — its tasks
+        // view inner-joins Lists — so dropping it loses nothing the user could see.
+        val importable = snapshot.tasks.filter { it.listId in listIds }
+        val importableIds = importable.mapTo(mutableSetOf()) { it.id }
+        val taskIds = mutableMapOf<Long, Long>()
+        val inserted = mutableListOf<Pair<LegacyTaskRow, TaskEntity>>()
+        val seen = mutableSetOf<Triple<Long, String, Instant?>>()
+
+        for (row in importable) {
+            val listId = listIds.getValue(row.listId)
+            val overrides = row.masterId != null && row.masterId in importableIds
+            val recurrenceId = row.recurrenceId.takeIf { overrides }
+            // A duplicate (list, uid, recurrence) would abort the whole import on
+            // the unique index; a fresh uid costs the row nothing it still has.
+            val uid = row.entity.uid.takeIf { seen.add(Triple(listId, it, recurrenceId)) }
+                ?: UUID.randomUUID().toString()
+            val entity = row.entity.copy(listId = listId, uid = uid, recurrenceId = recurrenceId)
+            val newId = taskDao.insert(entity)
+            taskIds[row.id] = newId
+            inserted += row to entity.copy(id = newId)
+        }
+
+        for ((row, entity) in inserted) {
+            val parentId = row.parentId?.let(taskIds::get)
+            val masterId = row.masterId?.let(taskIds::get)
+            if (parentId == null && masterId == null) continue
+            taskDao.update(entity.copy(parentId = parentId, masterId = masterId))
+        }
+
+        var alarmCount = 0
+        for (alarm in snapshot.alarms) {
+            val taskId = taskIds[alarm.taskId] ?: continue
+            alarmDao.insert(
+                TaskAlarmEntity(
+                    taskId = taskId,
+                    minutesBefore = alarm.minutesBefore,
+                    reference = alarm.reference,
+                    message = alarm.message,
+                ),
+            )
+            alarmCount++
+        }
+
+        return ImportCounts(lists = listIds.size, tasks = taskIds.size, alarms = alarmCount)
+    }
+
+    private fun verify(written: ImportCounts, before: ImportCounts) {
+        val after = tableCounts()
+        check(after.lists - before.lists == written.lists) {
+            "list count mismatch: ${after.lists - before.lists} != ${written.lists}"
+        }
+        check(after.tasks - before.tasks == written.tasks) {
+            "task count mismatch: ${after.tasks - before.tasks} != ${written.tasks}"
+        }
+        check(after.alarms - before.alarms == written.alarms) {
+            "alarm count mismatch: ${after.alarms - before.alarms} != ${written.alarms}"
+        }
+    }
+
+    /** Dropping the lists takes their tasks and alarms with them, by cascade. */
+    private fun truncate() {
+        val listDao = database.taskLists()
+        listDao.lists().forEach { listDao.delete(it.list.id) }
+    }
+
+    private fun tableCounts() = ImportCounts(
+        lists = count("task_lists"),
+        tasks = count("tasks"),
+        alarms = count("task_alarms"),
+    )
+
+    private fun count(table: String): Int =
+        database.query("SELECT COUNT(*) FROM $table", null).use {
+            if (it.moveToFirst()) it.getInt(0) else 0
+        }
+
+    // --- the source file ------------------------------------------------------
+
+    /**
+     * Renames the dmfs file, sidecars included, to `tasks.db.imported`. Never
+     * deletes it: for one release it is the only way back if the import turns out
+     * to be wrong on someone's device.
+     */
+    private fun archive(source: File): Boolean {
+        val target = File(source.parentFile, ARCHIVE_NAME)
+        if (!source.renameTo(target)) return false
+        for (suffix in SIDECARS) {
+            val sidecar = File(source.path + suffix)
+            if (sidecar.exists()) sidecar.renameTo(File(target.path + suffix))
+        }
+        return true
+    }
+
+    private suspend fun markDone() {
+        dataStore.edit { it[IMPORT_DONE] = true }
+    }
+
+    private fun CursorColumnReader.instant(name: String): Instant? =
+        getLong(name)?.let(Instant::fromEpochMilliseconds)
+
+    companion object {
+        const val LEGACY_NAME = "tasks.db"
+        const val ARCHIVE_NAME = "tasks.db.imported"
+
+        private const val ALARM_MIMETYPE = "vnd.android.cursor.item/alarm"
+        private const val REFERENCE_START = "2"
+        private val SIDECARS = listOf("-journal", "-wal", "-shm")
+        private val IMPORT_DONE = booleanPreferencesKey("legacy_import_done")
+    }
+}
+
+private class LegacySnapshot(
+    val lists: List<LegacyList>,
+    val tasks: List<LegacyTaskRow>,
+    val alarms: List<LegacyAlarm>,
+)
+
+private class LegacyList(val id: Long, val entity: TaskListEntity)
+
+private class LegacyTaskRow(
+    val id: Long,
+    val listId: Long,
+    val parentId: Long?,
+    val masterId: Long?,
+    val recurrenceId: Instant?,
+    val entity: TaskEntity,
+)
+
+private class LegacyAlarm(
+    val taskId: Long,
+    val minutesBefore: Int,
+    val reference: AlarmReference,
+    val message: String?,
+)

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/AccountDao.kt

@@ -0,0 +1,30 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.Dao
+import androidx.room.Insert
+import androidx.room.Query
+import androidx.room.Update
+import kotlin.time.Instant
+
+/** Reads and writes over `accounts`. Unused until sync lands. */
+@Dao
+interface AccountDao {
+
+    @Query("SELECT * FROM accounts ORDER BY display_name")
+    fun all(): List<AccountEntity>
+
+    @Query("SELECT * FROM accounts WHERE id = :accountId")
+    fun account(accountId: Long): AccountEntity?
+
+    @Insert
+    fun insert(account: AccountEntity): Long
+
+    @Update
+    fun update(account: AccountEntity)
+
+    @Query("UPDATE accounts SET last_sync_at = :at, last_sync_error = :error WHERE id = :accountId")
+    fun recordSync(accountId: Long, at: Instant?, error: String?)
+
+    @Query("DELETE FROM accounts WHERE id = :accountId")
+    fun delete(accountId: Long): Int
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/Converters.kt

@@ -0,0 +1,38 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.TypeConverter
+import de.jeanlucmakiola.agendula.domain.TaskStatus
+import de.jeanlucmakiola.agendula.domain.statusFromInt
+import de.jeanlucmakiola.agendula.domain.toInt
+import kotlin.time.Instant
+
+/**
+ * Storage encodings for the entity types SQLite has no column type for. Time is
+ * epoch millis; [TaskStatus] goes through the `domain` mappers so that numbering
+ * keeps its single home.
+ *
+ * `PRIORITY` deliberately has no converter — it is stored as the raw iCalendar
+ * integer, because [de.jeanlucmakiola.agendula.domain.Priority] is a lossy
+ * bucketing and a converter would apply it before the value reaches disk.
+ */
+object Converters {
+
+    @TypeConverter
+    fun instantToMillis(value: Instant?): Long? = value?.toEpochMilliseconds()
+
+    @TypeConverter
+    fun instantFromMillis(value: Long?): Instant? = value?.let(Instant::fromEpochMilliseconds)
+
+    @TypeConverter
+    fun statusToInt(value: TaskStatus): Int = value.toInt()
+
+    @TypeConverter
+    fun statusFrom(value: Int): TaskStatus = statusFromInt(value)
+
+    @TypeConverter
+    fun alarmReferenceToString(value: AlarmReference): String = value.name
+
+    @TypeConverter
+    fun alarmReferenceFrom(value: String): AlarmReference =
+        runCatching { AlarmReference.valueOf(value) }.getOrDefault(AlarmReference.DUE)
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/DatabaseCheckpoint.kt

@@ -0,0 +1,35 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.lifecycle.DefaultLifecycleObserver
+import androidx.lifecycle.LifecycleOwner
+import de.jeanlucmakiola.agendula.data.di.ApplicationScope
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Folds the write-ahead log back into the database file when the app goes to the
+ * background.
+ *
+ * Room runs in WAL mode, and Auto Backup copies files without checkpointing — so
+ * a `-wal` sidecar can hold writes the backed-up `.db` does not. The backup rules
+ * carry all three files, which already makes a restore consistent; this narrows
+ * the window further by ensuring the `.db` alone is usually current, which is what
+ * a restore onto a device that drops the sidecars falls back to.
+ */
+@Singleton
+class DatabaseCheckpoint @Inject constructor(
+    private val database: TasksDatabase,
+    @ApplicationScope private val scope: CoroutineScope,
+) : DefaultLifecycleObserver {
+
+    override fun onStop(owner: LifecycleOwner) {
+        scope.launch(Dispatchers.IO) {
+            runCatching {
+                database.openHelper.writableDatabase.query("PRAGMA wal_checkpoint(TRUNCATE)").close()
+            }
+        }
+    }
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/Entities.kt

@@ -0,0 +1,213 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.ColumnInfo
+import androidx.room.Entity
+import androidx.room.ForeignKey
+import androidx.room.Index
+import androidx.room.PrimaryKey
+import de.jeanlucmakiola.agendula.domain.PRIORITY_NONE
+import de.jeanlucmakiola.agendula.domain.TaskStatus
+import kotlin.time.Instant
+
+/**
+ * A CalDAV account. Empty until sync lands (`docs/SYNC.md` phase 2), but the FK
+ * from [TaskListEntity] exists from v1 so turning sync on never needs a
+ * migration. The app password is never stored here — Keystore only.
+ */
+@Entity(tableName = "accounts")
+data class AccountEntity(
+    @PrimaryKey(autoGenerate = true)
+    @ColumnInfo(name = "id") val id: Long = 0,
+    @ColumnInfo(name = "display_name") val displayName: String,
+    @ColumnInfo(name = "principal_url") val principalUrl: String? = null,
+    @ColumnInfo(name = "home_set_url") val homeSetUrl: String? = null,
+    @ColumnInfo(name = "username") val username: String? = null,
+    @ColumnInfo(name = "last_sync_at") val lastSyncAt: Instant? = null,
+    @ColumnInfo(name = "last_sync_error") val lastSyncError: String? = null,
+)
+
+/**
+ * A task list. [accountId] is nullable: `NULL` is a device-only list, and
+ * attaching one to an account later is a plain `UPDATE` rather than a data
+ * migration.
+ *
+ * Deleting an account detaches its lists (`SET NULL`) instead of deleting them,
+ * for the same reason [TaskEntity.parentId] does — removing an account is not
+ * an instruction to destroy the tasks it held.
+ */
+@Entity(
+    tableName = "task_lists",
+    foreignKeys = [
+        ForeignKey(
+            entity = AccountEntity::class,
+            parentColumns = ["id"],
+            childColumns = ["account_id"],
+            onDelete = ForeignKey.SET_NULL,
+        ),
+    ],
+    indices = [Index(value = ["account_id"])],
+)
+data class TaskListEntity(
+    @PrimaryKey(autoGenerate = true)
+    @ColumnInfo(name = "id") val id: Long = 0,
+    @ColumnInfo(name = "name") val name: String,
+    /** ARGB. */
+    @ColumnInfo(name = "color") val color: Int,
+    @ColumnInfo(name = "account_id") val accountId: Long? = null,
+    @ColumnInfo(name = "is_visible", defaultValue = "1") val isVisible: Boolean = true,
+    @ColumnInfo(name = "is_synced", defaultValue = "1") val isSynced: Boolean = true,
+    /** CalDAV owner display name. */
+    @ColumnInfo(name = "owner") val owner: String? = null,
+    @ColumnInfo(name = "is_read_only", defaultValue = "0") val isReadOnly: Boolean = false,
+    /** User ordering. */
+    @ColumnInfo(name = "sort_order", defaultValue = "0") val sortOrder: Int = 0,
+    /** Collection URL, relative to the account root. */
+    @ColumnInfo(name = "href") val href: String? = null,
+    @ColumnInfo(name = "ctag") val ctag: String? = null,
+    /** RFC 6578 sync token, per collection. */
+    @ColumnInfo(name = "sync_token") val syncToken: String? = null,
+    @ColumnInfo(name = "is_dirty", defaultValue = "0") val isDirty: Boolean = false,
+)
+
+/**
+ * A task. Series masters *and* `RECURRENCE-ID` overrides live in this table; an
+ * override is a row with [recurrenceId] set and [masterId] pointing at its
+ * master, sharing the master's [uid].
+ *
+ * [masterId] and [parentId] are different things: [parentId] is task hierarchy
+ * (`RELATED-TO;RELTYPE=PARENT`), [masterId] is recurrence. A row can carry both.
+ */
+@Entity(
+    tableName = "tasks",
+    foreignKeys = [
+        ForeignKey(
+            entity = TaskListEntity::class,
+            parentColumns = ["id"],
+            childColumns = ["list_id"],
+            onDelete = ForeignKey.CASCADE,
+        ),
+        // Deleting a series takes its overrides with it — they would otherwise be
+        // unreachable rows that still sync.
+        ForeignKey(
+            entity = TaskEntity::class,
+            parentColumns = ["id"],
+            childColumns = ["master_id"],
+            onDelete = ForeignKey.CASCADE,
+        ),
+        // Deleting a parent promotes its subtasks to top level rather than
+        // destroying work the user did not ask to lose.
+        ForeignKey(
+            entity = TaskEntity::class,
+            parentColumns = ["id"],
+            childColumns = ["parent_id"],
+            onDelete = ForeignKey.SET_NULL,
+        ),
+    ],
+    indices = [
+        Index(value = ["list_id", "is_deleted"]),
+        Index(value = ["parent_id"]),
+        Index(value = ["master_id", "recurrence_id"]),
+        Index(value = ["is_dirty"]),
+        // An override shares its master's UID, so (list_id, uid) alone would
+        // reject the very rows recurrence depends on. With recurrence_id NULL on
+        // the master and set on each override this reads as: one master and at
+        // most one override per occurrence, per UID, per list. Note SQLite treats
+        // NULLs as distinct in a unique index, so the master half is a statement
+        // of intent, not an enforced constraint.
+        Index(value = ["list_id", "uid", "recurrence_id"], unique = true),
+    ],
+)
+data class TaskEntity(
+    // identity
+    @PrimaryKey(autoGenerate = true)
+    @ColumnInfo(name = "id") val id: Long = 0,
+    @ColumnInfo(name = "list_id") val listId: Long,
+    /** RFC 4122 UUID, minted at creation in every mode, synced or not. */
+    @ColumnInfo(name = "uid") val uid: String,
+    @ColumnInfo(name = "href") val href: String? = null,
+    @ColumnInfo(name = "etag") val etag: String? = null,
+
+    // content
+    @ColumnInfo(name = "title") val title: String? = null,
+    @ColumnInfo(name = "description") val description: String? = null,
+    @ColumnInfo(name = "location") val location: String? = null,
+    @ColumnInfo(name = "url") val url: String? = null,
+    /** ARGB override for the list colour. */
+    @ColumnInfo(name = "color") val color: Int? = null,
+
+    // state
+    @ColumnInfo(name = "status", defaultValue = "0") val status: TaskStatus = TaskStatus.NEEDS_ACTION,
+    @ColumnInfo(name = "percent_complete") val percentComplete: Int? = null,
+    @ColumnInfo(name = "completed_at") val completedAt: Instant? = null,
+    /**
+     * Raw iCalendar `PRIORITY`: 0 none, 1 highest, 9 lowest. Stored unbucketed —
+     * [de.jeanlucmakiola.agendula.domain.Priority] folds 1–4 into HIGH, so
+     * converting on the way *in* would rewrite a server's `PRIORITY:3` as `1` and
+     * lose it on the next round-trip. The bucketing belongs to the mapper, which
+     * is where the UI needs it.
+     */
+    @ColumnInfo(name = "priority", defaultValue = "0") val priority: Int = PRIORITY_NONE,
+    /** RFC 5545 `CLASS`: 0 public, 1 private, 2 confidential. */
+    @ColumnInfo(name = "classification") val classification: Int? = null,
+
+    // time
+    @ColumnInfo(name = "dtstart") val dtstart: Instant? = null,
+    @ColumnInfo(name = "due") val due: Instant? = null,
+    /** RFC 5545 `DURATION`, verbatim. Mutually exclusive with [due]. */
+    @ColumnInfo(name = "duration") val duration: String? = null,
+    @ColumnInfo(name = "is_all_day", defaultValue = "0") val isAllDay: Boolean = false,
+    @ColumnInfo(name = "timezone") val timezone: String? = null,
+
+    // recurrence
+    @ColumnInfo(name = "rrule") val rrule: String? = null,
+    @ColumnInfo(name = "rdate") val rdate: String? = null,
+    @ColumnInfo(name = "exdate") val exdate: String? = null,
+    /** This row's `RECURRENCE-ID` anchor; `NULL` on a master. */
+    @ColumnInfo(name = "recurrence_id") val recurrenceId: Instant? = null,
+    /** The series this row overrides; `NULL` on a master. */
+    @ColumnInfo(name = "master_id") val masterId: Long? = null,
+
+    // hierarchy
+    @ColumnInfo(name = "parent_id") val parentId: Long? = null,
+    @ColumnInfo(name = "sort_order", defaultValue = "0") val sortOrder: Int = 0,
+
+    // audit
+    @ColumnInfo(name = "created_at") val createdAt: Instant? = null,
+    @ColumnInfo(name = "last_modified") val lastModified: Instant? = null,
+    @ColumnInfo(name = "sequence", defaultValue = "0") val sequence: Int = 0,
+
+    // sync
+    @ColumnInfo(name = "is_dirty", defaultValue = "0") val isDirty: Boolean = false,
+    /** Tombstone: deleted locally, still owed to a server. */
+    @ColumnInfo(name = "is_deleted", defaultValue = "0") val isDeleted: Boolean = false,
+    /**
+     * Raw unfolded iCalendar lines of every property we do not model, re-emitted
+     * verbatim on write so a round-trip cannot silently lose a field.
+     */
+    @ColumnInfo(name = "unknown_properties") val unknownProperties: String? = null,
+)
+
+/** What [TaskAlarmEntity.minutesBefore] counts back from. */
+enum class AlarmReference { DUE, START }
+
+/** A reminder lead on a task. Positive [minutesBefore] is *before* [reference]. */
+@Entity(
+    tableName = "task_alarms",
+    foreignKeys = [
+        ForeignKey(
+            entity = TaskEntity::class,
+            parentColumns = ["id"],
+            childColumns = ["task_id"],
+            onDelete = ForeignKey.CASCADE,
+        ),
+    ],
+    indices = [Index(value = ["task_id"])],
+)
+data class TaskAlarmEntity(
+    @PrimaryKey(autoGenerate = true)
+    @ColumnInfo(name = "id") val id: Long = 0,
+    @ColumnInfo(name = "task_id") val taskId: Long,
+    @ColumnInfo(name = "minutes_before") val minutesBefore: Int,
+    @ColumnInfo(name = "reference", defaultValue = "DUE") val reference: AlarmReference = AlarmReference.DUE,
+    @ColumnInfo(name = "message") val message: String? = null,
+)

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/Projections.kt

@@ -0,0 +1,26 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.ColumnInfo
+import androidx.room.Embedded
+
+/**
+ * A list plus its account's display name, which the domain
+ * [de.jeanlucmakiola.agendula.domain.TaskList] carries and groups by.
+ * `null` means a device-only list.
+ */
+data class TaskListRow(
+    @Embedded val list: TaskListEntity,
+    @ColumnInfo(name = "account_display_name") val accountDisplayName: String?,
+)
+
+/**
+ * A task plus the three columns of its list the domain
+ * [de.jeanlucmakiola.agendula.domain.Task] carries, so reading a screenful is
+ * one query rather than one per list.
+ */
+data class TaskRow(
+    @Embedded val task: TaskEntity,
+    @ColumnInfo(name = "list_name") val listName: String,
+    @ColumnInfo(name = "list_color") val listColor: Int,
+    @ColumnInfo(name = "account_display_name") val accountDisplayName: String?,
+)

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/RoomTaskMapper.kt

@@ -0,0 +1,114 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import de.jeanlucmakiola.agendula.domain.LocalAccount
+import de.jeanlucmakiola.agendula.domain.Task
+import de.jeanlucmakiola.agendula.domain.TaskList
+import de.jeanlucmakiola.agendula.domain.export.ExportTask
+import de.jeanlucmakiola.agendula.domain.priorityFromICal
+import de.jeanlucmakiola.agendula.domain.recurrence.RecurrenceSpec
+import kotlin.time.Instant
+
+/** Account type reported for a list attached to one of ours. */
+const val CALDAV_ACCOUNT_TYPE = "caldav"
+
+/** Maps Room rows to domain models. Pure + testable, like [de.jeanlucmakiola.agendula.data.tasks.TaskMapper]. */
+object RoomTaskMapper {
+
+    fun taskList(row: TaskListRow): TaskList = TaskList(
+        id = row.list.id,
+        name = row.list.name,
+        color = row.list.color,
+        // TaskList.accountName is non-null and the lists screen groups by it, so a
+        // list with no account still has to report something to group under.
+        accountName = row.accountDisplayName ?: LocalAccount.NAME,
+        accountType = if (row.list.accountId == null) LocalAccount.TYPE else CALDAV_ACCOUNT_TYPE,
+        isSynced = row.list.isSynced,
+        isVisible = row.list.isVisible,
+        owner = row.list.owner,
+    )
+
+    /**
+     * One occurrence of [row]. [occurrenceStart] is the occurrence's
+     * `RECURRENCE-ID` anchor and `null` for a task that does not recur;
+     * [start] / [due] are that occurrence's resolved times.
+     */
+    fun task(
+        row: TaskRow,
+        occurrenceStart: Instant? = null,
+        start: Instant? = row.task.dtstart,
+        due: Instant? = row.task.due,
+        distanceFromCurrent: Int? = null,
+    ): Task = Task(
+        taskId = row.task.id,
+        listId = row.task.listId,
+        title = row.task.title.orEmpty(),
+        description = row.task.description,
+        location = row.task.location,
+        url = row.task.url,
+        priority = priorityFromICal(row.task.priority),
+        status = row.task.status,
+        percentComplete = row.task.percentComplete,
+        start = start,
+        due = due,
+        isAllDay = row.task.isAllDay,
+        timeZone = row.task.timezone,
+        completedAt = row.task.completedAt,
+        listColor = row.listColor,
+        taskColor = row.task.color,
+        listName = row.listName,
+        accountName = row.accountDisplayName ?: LocalAccount.NAME,
+        parentId = row.task.parentId,
+        isRecurring = row.task.isRecurring,
+        occurrenceStart = occurrenceStart,
+        distanceFromCurrent = distanceFromCurrent,
+        created = row.task.createdAt,
+        lastModified = row.task.lastModified,
+    )
+
+    fun exportTask(task: TaskEntity): ExportTask = ExportTask(
+        taskId = task.id,
+        uid = task.uid,
+        title = task.title.orEmpty(),
+        description = task.description,
+        location = task.location,
+        url = task.url,
+        priority = priorityFromICal(task.priority),
+        status = task.status,
+        percentComplete = task.percentComplete,
+        start = task.dtstart,
+        due = task.due,
+        isAllDay = task.isAllDay,
+        completedAt = task.completedAt,
+        created = task.createdAt,
+        lastModified = task.lastModified,
+        rrule = task.rrule,
+        rdate = task.rdate,
+        parentId = task.parentId?.takeIf { it > 0 },
+    )
+}
+
+/** A row carries a recurrence rule if it has an `RRULE` or an `RDATE`. */
+val TaskEntity.isRecurring: Boolean
+    get() = !rrule.isNullOrBlank() || !rdate.isNullOrBlank()
+
+/**
+ * The series anchor: `DTSTART` when present, else `DUE`. A `VTODO` may carry only
+ * a due date, and RFC 5545 then anchors the recurrence on it — matching how the
+ * dmfs provider instantiated the same series.
+ */
+val TaskEntity.recurrenceAnchor: Instant?
+    get() = dtstart ?: due
+
+/** The rule set of this series, or `null` when it does not recur. */
+fun TaskEntity.recurrenceSpec(): RecurrenceSpec? {
+    if (!isRecurring) return null
+    val anchor = recurrenceAnchor ?: return null
+    return RecurrenceSpec(
+        rrule = rrule,
+        rdate = rdate,
+        exdate = exdate,
+        anchor = anchor,
+        isAllDay = isAllDay,
+        timeZone = timezone,
+    )
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/RoomTasksDataSource.kt

@@ -0,0 +1,282 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.InvalidationTracker
+import de.jeanlucmakiola.agendula.data.tasks.TaskQuery
+import de.jeanlucmakiola.agendula.data.tasks.TaskReminder
+import de.jeanlucmakiola.agendula.data.tasks.TaskWriteFailedException
+import de.jeanlucmakiola.agendula.data.tasks.TasksDataSource
+import de.jeanlucmakiola.agendula.domain.Task
+import de.jeanlucmakiola.agendula.domain.TaskForm
+import de.jeanlucmakiola.agendula.domain.TaskList
+import de.jeanlucmakiola.agendula.domain.export.ExportTask
+import de.jeanlucmakiola.agendula.domain.recurrence.ExpansionWindow
+import de.jeanlucmakiola.agendula.domain.recurrence.RecurrenceExpander
+import java.time.ZoneId
+import java.util.UUID
+import javax.inject.Inject
+import javax.inject.Singleton
+import kotlin.time.Clock
+import kotlin.time.Duration.Companion.days
+import kotlin.time.Instant
+
+/** How far either side of now a series is expanded. */
+private val WINDOW_BACK = 365.days
+private val WINDOW_FORWARD = 730.days
+
+private val OBSERVED_TABLES = arrayOf("tasks", "task_lists", "task_alarms", "accounts")
+
+/**
+ * [TasksDataSource] over Agendula's own Room store.
+ *
+ * The one structural difference from [de.jeanlucmakiola.agendula.data.tasks
+ * .AndroidTasksDataSource]: there is no materialised instances table, so a
+ * recurring series is expanded here, at read time, by [RecurrenceExpander].
+ * Nothing above this cares — the repository already filters and sorts in Kotlin.
+ */
+@Singleton
+class RoomTasksDataSource @Inject constructor(
+    private val database: TasksDatabase,
+) : TasksDataSource {
+
+    private val clock: Clock = Clock.System
+
+    private val tasks get() = database.tasks()
+    private val lists get() = database.taskLists()
+    private val alarms get() = database.alarms()
+
+    // --- reads ----------------------------------------------------------------
+
+    override fun taskLists(): List<TaskList> = lists.lists().map(RoomTaskMapper::taskList)
+
+    override fun tasks(query: TaskQuery): List<Task> {
+        val now = clock.now()
+        val overrides = tasks.allOverrides(query.listId).groupBy { it.masterId }
+        return tasks.tasks(query.listId, query.includeCompleted)
+            .flatMap { occurrencesOf(it, overrides[it.task.id].orEmpty(), now) }
+            .filter { query.includeCompleted || !it.isClosed }
+    }
+
+    override fun task(taskId: Long): Task? {
+        val row = tasks.task(taskId) ?: return null
+        // An override row is one occurrence in its own right; it names the
+        // occurrence it replaces rather than expanding to a series.
+        row.task.recurrenceId?.let { return RoomTaskMapper.task(row, occurrenceStart = it) }
+        val now = clock.now()
+        val occurrences = occurrencesOf(row, tasks.overrides(taskId), now)
+        return occurrences.firstOrNull { it.distanceFromCurrent == 0 } ?: occurrences.firstOrNull()
+    }
+
+    override fun subtasks(parentTaskId: Long): List<Task> {
+        val now = clock.now()
+        return tasks.subtasks(parentTaskId)
+            .flatMap { occurrencesOf(it, tasks.overrides(it.task.id), now) }
+    }
+
+    override fun exportTasks(listId: Long): List<ExportTask> =
+        tasks.exportTasks(listId).map(RoomTaskMapper::exportTask)
+
+    override fun alarms(): Map<Long, TaskReminder> =
+        alarms.all().associate {
+            it.taskId to TaskReminder(
+                minutesBefore = it.minutesBefore,
+                fromStart = it.reference == AlarmReference.START,
+            )
+        }
+
+    /**
+     * Every occurrence of [row] inside the expansion window, with any
+     * `RECURRENCE-ID` override substituted for the occurrence it replaces.
+     *
+     * A non-recurring task is its own single occurrence and carries a null
+     * [Task.occurrenceStart], so it keys and edits by task id exactly as before.
+     */
+    private fun occurrencesOf(row: TaskRow, overrides: List<TaskEntity>, now: Instant): List<Task> {
+        val spec = row.task.recurrenceSpec() ?: return listOf(RoomTaskMapper.task(row))
+        val window = ExpansionWindow(
+            from = now - WINDOW_BACK,
+            until = now + WINDOW_FORWARD,
+            pivot = now,
+        )
+        val anchors = RecurrenceExpander.expand(spec, window)
+        if (anchors.isEmpty()) return emptyList()
+
+        val distances = RecurrenceExpander.distancesFromCurrent(anchors, now)
+        val byAnchor = overrides.associateBy { it.recurrenceId }
+
+        return anchors.mapIndexedNotNull { index, anchor ->
+            val override = byAnchor[anchor]
+            if (override != null) {
+                RoomTaskMapper.task(
+                    row = row.copy(task = override),
+                    occurrenceStart = anchor,
+                    start = override.dtstart,
+                    due = override.due,
+                    distanceFromCurrent = distances[index],
+                )
+            } else {
+                val (start, due) = occurrenceTimes(row.task, anchor)
+                RoomTaskMapper.task(
+                    row = row,
+                    occurrenceStart = anchor,
+                    start = start,
+                    due = due,
+                    distanceFromCurrent = distances[index],
+                )
+            }
+        }
+    }
+
+    /**
+     * One occurrence's resolved start and due. A timed series keeps each
+     * occurrence's duration; a due-anchored one has no start to offset from, so
+     * the anchor *is* the due date.
+     */
+    private fun occurrenceTimes(master: TaskEntity, anchor: Instant): Pair<Instant?, Instant?> {
+        if (master.dtstart == null) return null to anchor
+        val length = master.due?.let { it - master.dtstart }
+        return anchor to length?.let { anchor + it }
+    }
+
+    // --- writes ---------------------------------------------------------------
+
+    override fun insertTask(form: TaskForm): Long {
+        if (lists.exists(form.listId) == 0) throw TaskWriteFailedException("insert task: no list ${form.listId}")
+        val entity = TaskFormWriter.newTask(form, uid = UUID.randomUUID().toString(), now = clock.now(), tzId = zone())
+        return tasks.insert(entity)
+    }
+
+    override fun updateTask(taskId: Long, form: TaskForm) {
+        val current = tasks.entity(taskId) ?: throw TaskWriteFailedException("update task $taskId")
+        tasks.update(TaskFormWriter.apply(current, form, clock.now(), zone()))
+    }
+
+    /**
+     * Writes one occurrence as a `RECURRENCE-ID` override — RFC 5545's model, and
+     * what every other CalDAV client expects to receive. The dmfs provider
+     * detached the occurrence into a brand-new task with its own UID instead,
+     * which is the model least compatible with sync; the override shares its
+     * master's UID, which is exactly what makes it an override.
+     */
+    override fun updateInstance(taskId: Long, occurrenceStart: Instant, form: TaskForm) {
+        val master = tasks.entity(taskId) ?: throw TaskWriteFailedException("update instance $taskId")
+        val now = clock.now()
+        val existing = tasks.override(taskId, occurrenceStart)
+        if (existing != null) {
+            tasks.update(TaskFormWriter.apply(existing, form, now, zone()))
+            return
+        }
+        val (start, due) = occurrenceTimes(master, occurrenceStart)
+        val fork = TaskFormWriter.apply(
+            newOverride(master, taskId, occurrenceStart, start, due),
+            form,
+            now,
+            zone(),
+        )
+        // The list and parent come from the master: moving one occurrence between
+        // lists or parents is not something the override model expresses.
+        val id = tasks.insert(fork.copy(listId = master.listId, parentId = master.parentId))
+        alarms.forTask(taskId).firstOrNull()?.let { alarms.replaceForTask(id, it) }
+    }
+
+    override fun setAlarm(taskId: Long, minutesBeforeDue: Int?) {
+        alarms.replaceForTask(
+            taskId,
+            minutesBeforeDue?.let { TaskAlarmEntity(taskId = taskId, minutesBefore = it) },
+        )
+    }
+
+    override fun setCompleted(taskId: Long, completed: Boolean) {
+        val current = tasks.entity(taskId) ?: throw TaskWriteFailedException("complete task $taskId")
+        tasks.update(TaskFormWriter.completed(current, completed, clock.now()))
+    }
+
+    /**
+     * Ticking one occurrence forks a `RECURRENCE-ID` override carrying the
+     * completion — the same model [updateInstance] writes. Writing the status onto
+     * the master instead would close the series: the master is what
+     * [TaskDao.tasks] filters on, so every occurrence, past and future, would
+     * leave every list at once.
+     */
+    override fun setCompletedInstance(taskId: Long, occurrenceStart: Instant, completed: Boolean) {
+        val master = tasks.entity(taskId) ?: throw TaskWriteFailedException("complete instance $taskId")
+        // Not a series master — an override, or a plain task the caller handed an
+        // anchor for. Either way this row *is* the occurrence.
+        if (master.recurrenceSpec() == null) return setCompleted(taskId, completed)
+
+        val now = clock.now()
+        tasks.override(taskId, occurrenceStart)?.let {
+            tasks.update(TaskFormWriter.completed(it, completed, now))
+            return
+        }
+        val (start, due) = occurrenceTimes(master, occurrenceStart)
+        val fork = TaskFormWriter.completed(newOverride(master, taskId, occurrenceStart, start, due), completed, now)
+        val id = tasks.insert(fork)
+        alarms.forTask(taskId).firstOrNull()?.let { alarms.replaceForTask(id, it) }
+    }
+
+    /**
+     * A blank override row for one occurrence of [master]: same UID (that is what
+     * makes it an override rather than a separate task), the series fields
+     * stripped, and no `href`/`etag` because the server has never seen it.
+     */
+    private fun newOverride(
+        master: TaskEntity,
+        masterId: Long,
+        occurrenceStart: Instant,
+        start: Instant?,
+        due: Instant?,
+    ): TaskEntity = master.copy(
+        id = 0,
+        masterId = masterId,
+        recurrenceId = occurrenceStart,
+        dtstart = start,
+        due = due,
+        rrule = null,
+        rdate = null,
+        exdate = null,
+        href = null,
+        etag = null,
+    )
+
+    /**
+     * Hard delete for a row no server knows about, tombstone for one that is
+     * still owed to a collection. `master_id` cascades, so deleting a series
+     * takes its overrides with it.
+     */
+    override fun deleteTask(taskId: Long) {
+        val current = tasks.entity(taskId) ?: return
+        val listAccount = lists.entity(current.listId)?.accountId
+        if (listAccount == null) tasks.delete(taskId) else tasks.markDeleted(taskId, clock.now())
+    }
+
+    override fun createLocalList(name: String, color: Int): Long =
+        lists.insert(TaskListEntity(name = name.trim(), color = color))
+
+    override fun updateList(listId: Long, name: String, color: Int) {
+        val current = lists.entity(listId) ?: throw TaskWriteFailedException("update list $listId")
+        // Only an account-backed collection owes a server a PROPPATCH; a
+        // device-only list has nothing to be dirty for.
+        lists.update(
+            current.copy(
+                name = name.trim(),
+                color = color,
+                isDirty = current.accountId != null,
+            ),
+        )
+    }
+
+    /** `tasks.list_id` is `ON DELETE CASCADE`, so the list's tasks go with it. */
+    override fun deleteList(listId: Long) = lists.delete(listId)
+
+    // --- observation ----------------------------------------------------------
+
+    override fun registerObserver(onChange: () -> Unit): AutoCloseable {
+        val observer = object : InvalidationTracker.Observer(OBSERVED_TABLES) {
+            override fun onInvalidated(tables: Set<String>) = onChange()
+        }
+        database.invalidationTracker.addObserver(observer)
+        return AutoCloseable { database.invalidationTracker.removeObserver(observer) }
+    }
+
+    private fun zone(): String = ZoneId.systemDefault().id
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/TaskAlarmDao.kt

@@ -0,0 +1,35 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.Dao
+import androidx.room.Insert
+import androidx.room.Query
+import androidx.room.Transaction
+
+/** Reads and writes over `task_alarms`. */
+@Dao
+interface TaskAlarmDao {
+
+    /** Every reminder in the store, for one scheduler pass. */
+    @Query("SELECT * FROM task_alarms")
+    fun all(): List<TaskAlarmEntity>
+
+    @Query("SELECT * FROM task_alarms WHERE task_id = :taskId")
+    fun forTask(taskId: Long): List<TaskAlarmEntity>
+
+    @Insert
+    fun insert(alarm: TaskAlarmEntity): Long
+
+    @Query("DELETE FROM task_alarms WHERE task_id = :taskId")
+    fun deleteForTask(taskId: Long): Int
+
+    /**
+     * Set the task's only reminder, or clear it with `null`. The row that lands is
+     * always a new one — the id is cleared so an alarm lifted off another task
+     * (forking an occurrence copies the master's) inserts instead of colliding.
+     */
+    @Transaction
+    fun replaceForTask(taskId: Long, alarm: TaskAlarmEntity?) {
+        deleteForTask(taskId)
+        alarm?.let { insert(it.copy(id = 0, taskId = taskId)) }
+    }
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/TaskDao.kt

@@ -0,0 +1,134 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.Dao
+import androidx.room.Insert
+import androidx.room.Query
+import androidx.room.Update
+import de.jeanlucmakiola.agendula.domain.TaskStatus
+import kotlin.time.Instant
+
+/**
+ * Reads and writes over `tasks`.
+ *
+ * Reads split masters from overrides on purpose: [tasks] returns the rows a
+ * recurrence expander expands (a non-recurring task is its own single
+ * occurrence), and [allOverrides] / [overrides] return the
+ * `RECURRENCE-ID` rows that replace individual occurrences. Nothing here
+ * expands anything — that is phase 2's job, in Kotlin.
+ */
+@Dao
+interface TaskDao {
+
+    // --- reads ----------------------------------------------------------------
+
+    /**
+     * Master (and non-recurring) rows, optionally narrowed to one list. Closed
+     * tasks — `COMPLETED` and `CANCELLED` — are excluded unless
+     * [includeCompleted]; tombstones always are.
+     */
+    @Query(
+        """
+        SELECT t.*, l.name AS list_name, l.color AS list_color,
+               a.display_name AS account_display_name
+        FROM tasks t
+        JOIN task_lists l ON l.id = t.list_id
+        LEFT JOIN accounts a ON a.id = l.account_id
+        WHERE t.is_deleted = 0
+          AND t.master_id IS NULL
+          AND (:listId IS NULL OR t.list_id = :listId)
+          AND (:includeCompleted = 1 OR t.status NOT IN (2, 3))
+        """
+    )
+    fun tasks(listId: Long?, includeCompleted: Boolean): List<TaskRow>
+
+    @Query(
+        """
+        SELECT t.*, l.name AS list_name, l.color AS list_color,
+               a.display_name AS account_display_name
+        FROM tasks t
+        JOIN task_lists l ON l.id = t.list_id
+        LEFT JOIN accounts a ON a.id = l.account_id
+        WHERE t.id = :taskId AND t.is_deleted = 0
+        """
+    )
+    fun task(taskId: Long): TaskRow?
+
+    @Query(
+        """
+        SELECT t.*, l.name AS list_name, l.color AS list_color,
+               a.display_name AS account_display_name
+        FROM tasks t
+        JOIN task_lists l ON l.id = t.list_id
+        LEFT JOIN accounts a ON a.id = l.account_id
+        WHERE t.parent_id = :parentTaskId AND t.is_deleted = 0 AND t.master_id IS NULL
+        """
+    )
+    fun subtasks(parentTaskId: Long): List<TaskRow>
+
+    @Query("SELECT * FROM tasks WHERE id = :taskId")
+    fun entity(taskId: Long): TaskEntity?
+
+    /**
+     * Every override, optionally narrowed to one list — read alongside [tasks] so
+     * expansion can replace the occurrences they override in one pass rather than
+     * querying per series.
+     */
+    @Query(
+        """
+        SELECT * FROM tasks
+        WHERE master_id IS NOT NULL AND is_deleted = 0
+          AND (:listId IS NULL OR list_id = :listId)
+        """
+    )
+    fun allOverrides(listId: Long?): List<TaskEntity>
+
+    @Query("SELECT * FROM tasks WHERE master_id = :masterId AND is_deleted = 0")
+    fun overrides(masterId: Long): List<TaskEntity>
+
+    @Query(
+        "SELECT * FROM tasks WHERE master_id = :masterId AND recurrence_id IS :recurrenceId AND is_deleted = 0"
+    )
+    fun override(masterId: Long, recurrenceId: Instant?): TaskEntity?
+
+    @Query("SELECT * FROM tasks WHERE list_id = :listId AND uid = :uid AND recurrence_id IS :recurrenceId")
+    fun byUid(listId: Long, uid: String, recurrenceId: Instant? = null): TaskEntity?
+
+    /** Masters only, tombstones excluded — what an `.ics` export writes. */
+    @Query("SELECT * FROM tasks WHERE list_id = :listId AND is_deleted = 0 AND master_id IS NULL")
+    fun exportTasks(listId: Long): List<TaskEntity>
+
+    @Query("SELECT * FROM tasks WHERE is_dirty = 1")
+    fun dirty(): List<TaskEntity>
+
+    // --- writes ---------------------------------------------------------------
+
+    @Insert
+    fun insert(task: TaskEntity): Long
+
+    @Update
+    fun update(task: TaskEntity): Int
+
+    @Query(
+        """
+        UPDATE tasks SET status = :status, percent_complete = :percentComplete,
+               completed_at = :completedAt, last_modified = :lastModified, is_dirty = :dirty
+        WHERE id = :taskId
+        """
+    )
+    fun setCompletion(
+        taskId: Long,
+        status: TaskStatus,
+        percentComplete: Int?,
+        completedAt: Instant?,
+        lastModified: Instant?,
+        dirty: Boolean,
+    ): Int
+
+    /** Hard delete. Used when the row was never on a server. */
+    @Query("DELETE FROM tasks WHERE id = :taskId")
+    fun delete(taskId: Long): Int
+
+    /** Tombstone, for a row a server still knows about. */
+    @Query("UPDATE tasks SET is_deleted = 1, is_dirty = 1, last_modified = :at WHERE id = :taskId")
+    fun markDeleted(taskId: Long, at: Instant?): Int
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/TaskFormWriter.kt

@@ -0,0 +1,91 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import de.jeanlucmakiola.agendula.domain.TaskForm
+import de.jeanlucmakiola.agendula.domain.TaskStatus
+import de.jeanlucmakiola.agendula.domain.toICal
+import kotlin.time.Instant
+
+private const val MILLIS_PER_DAY = 24L * 60 * 60 * 1000
+
+/** Floor to UTC midnight when [allDay], else pass through unchanged. */
+internal fun Instant.forAllDay(allDay: Boolean): Instant =
+    if (!allDay) this
+    else Instant.fromEpochMilliseconds(
+        Math.floorDiv(toEpochMilliseconds(), MILLIS_PER_DAY) * MILLIS_PER_DAY,
+    )
+
+/**
+ * Applies a [TaskForm] to a [TaskEntity]. Pure, so the semantics below are
+ * testable on the JVM without a database.
+ *
+ * This is the Room counterpart of
+ * [de.jeanlucmakiola.agendula.data.tasks.TaskWriteMapper], which stays for
+ * External mode. It is a separate object rather than a shared one because most
+ * of what that mapper does is work around the provider — clearing `DURATION`
+ * because the provider validates a merged row, writing `STATUS` both ways
+ * because the provider auto-completes at 100% but will not reopen below it. Here
+ * those rules are ours to state directly.
+ */
+object TaskFormWriter {
+
+    /** A brand-new task. [uid] is minted by the caller and never null. */
+    fun newTask(form: TaskForm, uid: String, now: Instant, tzId: String): TaskEntity =
+        apply(
+            TaskEntity(listId = form.listId, uid = uid, createdAt = now),
+            form,
+            now,
+            tzId,
+        )
+
+    /** [current] with [form] applied. Identity, recurrence and sync columns are left alone. */
+    fun apply(current: TaskEntity, form: TaskForm, now: Instant, tzId: String): TaskEntity {
+        val percent = form.percentComplete?.coerceIn(0, 100)
+        val timed = !form.isAllDay && (form.start != null || form.due != null)
+        return current.copy(
+            listId = form.listId,
+            title = form.title.trim(),
+            description = form.description?.trim()?.ifBlank { null },
+            priority = form.priority.toICal(),
+            percentComplete = percent,
+            status = statusFor(percent, current.status),
+            completedAt = completedAtFor(percent, current, now),
+            dtstart = form.start?.forAllDay(form.isAllDay),
+            due = form.due?.forAllDay(form.isAllDay),
+            // DUE and DURATION are mutually exclusive (RFC 5545 §3.6.2).
+            duration = null,
+            isAllDay = form.isAllDay,
+            timezone = if (timed) tzId else null,
+            parentId = form.parentId?.takeIf { it > 0 },
+            lastModified = now,
+            isDirty = true,
+        )
+    }
+
+    /** The completion triple, for the standalone complete toggle. */
+    fun completed(current: TaskEntity, completed: Boolean, now: Instant): TaskEntity = current.copy(
+        status = if (completed) TaskStatus.COMPLETED else TaskStatus.NEEDS_ACTION,
+        percentComplete = if (completed) 100 else null,
+        completedAt = if (completed) now else null,
+        lastModified = now,
+        isDirty = true,
+    )
+
+    /**
+     * A form carrying no percent leaves status alone — the standalone toggle stays
+     * authoritative. Otherwise progress and status move together in both
+     * directions, which is the asymmetry the provider never had: it auto-completed
+     * at 100% but would not reopen below it, stranding a task "done at 75%".
+     */
+    private fun statusFor(percent: Int?, current: TaskStatus): TaskStatus = when {
+        percent == null -> current
+        percent >= 100 -> TaskStatus.COMPLETED
+        percent > 0 -> TaskStatus.IN_PROCESS
+        else -> TaskStatus.NEEDS_ACTION
+    }
+
+    private fun completedAtFor(percent: Int?, current: TaskEntity, now: Instant): Instant? = when {
+        percent == null -> current.completedAt
+        percent >= 100 -> current.completedAt ?: now
+        else -> null
+    }
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/TaskListDao.kt

@@ -0,0 +1,51 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.Dao
+import androidx.room.Insert
+import androidx.room.Query
+import androidx.room.Update
+
+/** Reads and writes over `task_lists`. Synchronous, like the seam above it. */
+@Dao
+interface TaskListDao {
+
+    @Query(
+        """
+        SELECT l.*, a.display_name AS account_display_name
+        FROM task_lists l LEFT JOIN accounts a ON a.id = l.account_id
+        ORDER BY a.display_name, l.sort_order, l.name
+        """
+    )
+    fun lists(): List<TaskListRow>
+
+    @Query(
+        """
+        SELECT l.*, a.display_name AS account_display_name
+        FROM task_lists l LEFT JOIN accounts a ON a.id = l.account_id
+        WHERE l.id = :listId
+        """
+    )
+    fun list(listId: Long): TaskListRow?
+
+    @Query("SELECT * FROM task_lists WHERE id = :listId")
+    fun entity(listId: Long): TaskListEntity?
+
+    @Query("SELECT COUNT(*) FROM task_lists WHERE id = :listId")
+    fun exists(listId: Long): Int
+
+    @Insert
+    fun insert(list: TaskListEntity): Long
+
+    @Update
+    fun update(list: TaskListEntity)
+
+    @Query("UPDATE task_lists SET is_visible = :visible WHERE id = :listId")
+    fun setVisible(listId: Long, visible: Boolean)
+
+    /** Attach a list to an account, or detach it with `null`. */
+    @Query("UPDATE task_lists SET account_id = :accountId WHERE id = :listId")
+    fun setAccount(listId: Long, accountId: Long?)
+
+    @Query("DELETE FROM task_lists WHERE id = :listId")
+    fun delete(listId: Long)
+}

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/TasksDatabase.kt

@@ -0,0 +1,34 @@
+package de.jeanlucmakiola.agendula.data.tasks.room
+
+import androidx.room.Database
+import androidx.room.RoomDatabase
+import androidx.room.TypeConverters
+
+/**
+ * Agendula's own task store (`docs/OWN-STORE.md`). Four tables, designed from
+ * what the app actually reads and writes plus RFC 5545's `VTODO`.
+ *
+ * Schemas are exported to `app/schemas/` and committed, so a future version can
+ * be migration-tested against this one.
+ */
+@Database(
+    entities = [
+        AccountEntity::class,
+        TaskListEntity::class,
+        TaskEntity::class,
+        TaskAlarmEntity::class,
+    ],
+    version = 1,
+    exportSchema = true,
+)
+@TypeConverters(Converters::class)
+abstract class TasksDatabase : RoomDatabase() {
+    abstract fun taskLists(): TaskListDao
+    abstract fun tasks(): TaskDao
+    abstract fun alarms(): TaskAlarmDao
+    abstract fun accounts(): AccountDao
+
+    companion object {
+        const val NAME = "agendula-tasks.db"
+    }
+}

app/src/main/java/de/jeanlucmakiola/agendula/domain/AllDayTime.kt

@@ -0,0 +1,42 @@
+package de.jeanlucmakiola.agendula.domain
+
+import java.time.ZoneId
+import java.time.ZoneOffset
+import kotlin.time.Instant
+
+/**
+ * All-day tasks are date-only in iCalendar. OpenTasks reads them back through
+ * `DateTime.toAllDay()`, which discards the time-of-day and resolves the
+ * remaining date against UTC — so the storage convention is **UTC midnight of
+ * the intended calendar date, with a null timezone**. Timed tasks, by contrast,
+ * are ordinary instants rendered in the device's zone.
+ *
+ * These two conventions disagree about which day a given instant is, which is
+ * why every all-day value needs an explicit conversion rather than a raw
+ * `Instant` passed straight through.
+ */
+
+/** UTC midnight of [date] — the storage form for an all-day value. */
+fun allDayInstantOf(date: java.time.LocalDate): Instant =
+    Instant.fromEpochMilliseconds(date.atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli())
+
+/**
+ * The calendar date this instant denotes: read in UTC for [allDay] values,
+ * in [zone] for timed ones.
+ */
+fun Instant.calendarDate(allDay: Boolean, zone: ZoneId = ZoneId.systemDefault()): java.time.LocalDate =
+    java.time.Instant.ofEpochMilli(toEpochMilliseconds())
+        .atZone(if (allDay) ZoneOffset.UTC else zone)
+        .toLocalDate()
+
+/**
+ * Move an instant across the two conventions when the all-day switch flips, so
+ * the day the user is looking at stays put. Without this, toggling all-day off
+ * turns a UTC-midnight value into "02:00" in Berlin (or the previous day, 19:00,
+ * in New York) — reading to the user as "the time reset itself".
+ */
+fun Instant.rebasedForAllDay(allDay: Boolean, zone: ZoneId = ZoneId.systemDefault()): Instant =
+    if (allDay) allDayInstantOf(calendarDate(allDay = false, zone = zone))
+    else Instant.fromEpochMilliseconds(
+        calendarDate(allDay = true).atStartOfDay(zone).toInstant().toEpochMilli(),
+    )

app/src/main/java/de/jeanlucmakiola/agendula/domain/Models.kt

@@ -1,6 +1,5 @@
 package de.jeanlucmakiola.agendula.domain
 
-import de.jeanlucmakiola.agendula.data.tasks.TasksContract
 import kotlin.time.Instant
 
 /** A task list (the `tasklists` table). Lists group under their account. */
@@ -15,7 +14,8 @@ data class TaskList(
     val owner: String?,
 ) {
     /** A device-only list Agendula (or another app) created locally, not synced. */
-    val isLocal: Boolean get() = accountType == TasksContract.LOCAL_ACCOUNT_TYPE
+    val isLocal: Boolean
+        get() = accountType == LocalAccount.TYPE || accountType == LocalAccount.DMFS_TYPE
 }
 
 enum class TaskStatus { NEEDS_ACTION, IN_PROCESS, COMPLETED, CANCELLED }
@@ -24,11 +24,11 @@ enum class TaskStatus { NEEDS_ACTION, IN_PROCESS, COMPLETED, CANCELLED }
 enum class Priority { NONE, LOW, MEDIUM, HIGH }
 
 /**
- * A task occurrence as read from the `instances` view. [id] is the instance row
- * id; [taskId] is the underlying `tasks._id` and the stable target for edits.
+ * One occurrence of a task. [taskId] is the underlying task row and the stable
+ * target for edits and navigation; [occurrenceStart] distinguishes occurrences of
+ * the same series.
  */
 data class Task(
-    val id: Long,
     val taskId: Long,
     val listId: Long,
     val title: String,
@@ -48,7 +48,22 @@ data class Task(
     val listName: String?,
     val accountName: String?,
     val parentId: Long?,
+    /**
+     * This row carries a recurrence rule, so it is one occurrence of a series and
+     * [start]/[due] are that occurrence's resolved times — *not* the master's
+     * anchor. Edits go through
+     * [de.jeanlucmakiola.agendula.data.tasks.TasksDataSource.updateInstance], which
+     * forks a `RECURRENCE-ID` override instead of re-anchoring the series.
+     */
     val isRecurring: Boolean,
+    /**
+     * This occurrence's `RECURRENCE-ID` anchor — what identifies it within its
+     * series — or `null` when the task does not recur. Together with [taskId] it
+     * is a stable, collision-free identity for an occurrence, which is what list
+     * keys and [de.jeanlucmakiola.agendula.data.tasks.TasksDataSource.updateInstance]
+     * address it by.
+     */
+    val occurrenceStart: Instant? = null,
     val distanceFromCurrent: Int?,
     val created: Instant?,
     val lastModified: Instant?,
@@ -65,6 +80,15 @@ data class Task(
     val isSubtask: Boolean get() = parentId != null && parentId > 0
     /** The task's own colour if set, else the list colour. */
     val effectiveColor: Int get() = taskColor ?: listColor
+
+    /**
+     * Stable identity for a lazy-list key. Two occurrences of one series can show
+     * up in the same list, so [taskId] alone is not unique — and folding
+     * `(taskId, occurrenceStart)` into a Long could collide, which as a Compose
+     * key is a visible bug.
+     */
+    val occurrenceKey: String
+        get() = if (occurrenceStart == null) "$taskId" else "$taskId@${occurrenceStart.toEpochMilliseconds()}"
 }
 
 /** Detail bundle: a task, its parent (if it's a subtask), and its direct children. */
@@ -85,22 +109,22 @@ fun priorityFromICal(value: Int?): Priority = when {
 
 /** Representative iCalendar priority for a bucket (1 high, 5 medium, 9 low). */
 fun Priority.toICal(): Int = when (this) {
-    Priority.NONE -> TasksContract.PRIORITY_NONE
+    Priority.NONE -> PRIORITY_NONE
     Priority.HIGH -> 1
     Priority.MEDIUM -> 5
     Priority.LOW -> 9
 }
 
 fun statusFromInt(value: Int?): TaskStatus = when (value) {
-    TasksContract.STATUS_IN_PROCESS -> TaskStatus.IN_PROCESS
-    TasksContract.STATUS_COMPLETED -> TaskStatus.COMPLETED
-    TasksContract.STATUS_CANCELLED -> TaskStatus.CANCELLED
+    ICalStatus.IN_PROCESS -> TaskStatus.IN_PROCESS
+    ICalStatus.COMPLETED -> TaskStatus.COMPLETED
+    ICalStatus.CANCELLED -> TaskStatus.CANCELLED
     else -> TaskStatus.NEEDS_ACTION
 }
 
 fun TaskStatus.toInt(): Int = when (this) {
-    TaskStatus.NEEDS_ACTION -> TasksContract.STATUS_NEEDS_ACTION
-    TaskStatus.IN_PROCESS -> TasksContract.STATUS_IN_PROCESS
-    TaskStatus.COMPLETED -> TasksContract.STATUS_COMPLETED
-    TaskStatus.CANCELLED -> TasksContract.STATUS_CANCELLED
+    TaskStatus.NEEDS_ACTION -> ICalStatus.NEEDS_ACTION
+    TaskStatus.IN_PROCESS -> ICalStatus.IN_PROCESS
+    TaskStatus.COMPLETED -> ICalStatus.COMPLETED
+    TaskStatus.CANCELLED -> ICalStatus.CANCELLED
 }

app/src/main/java/de/jeanlucmakiola/agendula/domain/TaskConstants.kt

@@ -0,0 +1,30 @@
+package de.jeanlucmakiola.agendula.domain
+
+/**
+ * iCalendar `STATUS` values for a `VTODO`, as integers.
+ *
+ * These live in `domain` rather than being read out of a provider contract: the
+ * numbering is Agendula's own storage encoding as much as it is dmfs's, and the
+ * domain layer must not depend on the data layer to map its own enums.
+ */
+object ICalStatus {
+    const val NEEDS_ACTION = 0
+    const val IN_PROCESS = 1
+    const val COMPLETED = 2
+    const val CANCELLED = 3
+}
+
+/** Priority 0 means "no priority"; 1 is highest, 9 lowest (RFC 5545 §3.8.1.9). */
+const val PRIORITY_NONE = 0
+
+/** How a device-only list identifies its (non-existent) account. */
+object LocalAccount {
+    /** Shown as the section header above device-only lists. */
+    const val NAME = "Local"
+
+    /** What Agendula's own store reports for a list with no account. */
+    const val TYPE = "local"
+
+    /** What a dmfs-derived provider reports in External mode. */
+    const val DMFS_TYPE = "org.dmfs.account.LOCAL"
+}

app/src/main/java/de/jeanlucmakiola/agendula/domain/export/ExportModels.kt

@@ -0,0 +1,66 @@
+package de.jeanlucmakiola.agendula.domain.export
+
+import de.jeanlucmakiola.agendula.domain.Priority
+import de.jeanlucmakiola.agendula.domain.TaskStatus
+import kotlin.time.Instant
+
+/**
+ * One task as it goes out to iCalendar — a **master** task, not an occurrence.
+ *
+ * Deliberately not [de.jeanlucmakiola.agendula.domain.Task]. That model is read
+ * from the `instances` view, where a recurring task appears once per occurrence
+ * with resolved times and no rule; exporting from it would write the same task
+ * fifty times and lose the RRULE that generated them. Export reads the `tasks`
+ * table instead, and needs two fields the UI never asks for ([uid], [rrule]).
+ */
+data class ExportTask(
+    /** `tasks._id` — the fallback identity when [uid] is absent. */
+    val taskId: Long,
+    /**
+     * The iCalendar UID, or `null` for a task created on this device and never
+     * synced. The dmfs provider only lets a *sync adapter* assign one, so in Local
+     * mode this is null for everything — see [ICalendarWriter.uidFor], which
+     * synthesises a stable substitute rather than emitting a VTODO with no UID.
+     */
+    val uid: String?,
+    val title: String,
+    val description: String?,
+    val location: String?,
+    val url: String?,
+    val priority: Priority,
+    val status: TaskStatus,
+    val percentComplete: Int?,
+    val start: Instant?,
+    val due: Instant?,
+    val isAllDay: Boolean,
+    val completedAt: Instant?,
+    val created: Instant?,
+    val lastModified: Instant?,
+    /** Raw `RRULE` value as stored, without the `RRULE:` name. Null when non-recurring. */
+    val rrule: String?,
+    /** Raw `RDATE` value as stored. Null when absent. */
+    val rdate: String?,
+    /** `tasks._id` of the parent, for `RELATED-TO;RELTYPE=PARENT`. */
+    val parentId: Long?,
+)
+
+/** A task list and everything in it, ready to become one `.ics` document. */
+data class ExportList(
+    val listId: Long,
+    val name: String,
+    val accountName: String,
+    val tasks: List<ExportTask>,
+)
+
+/** A single file the export produced: [fileName] and its finished bytes. */
+data class ExportDocument(
+    val fileName: String,
+    val content: ByteArray,
+) {
+    // ByteArray gets identity equals/hashCode, which makes this data class lie.
+    override fun equals(other: Any?): Boolean =
+        this === other ||
+            (other is ExportDocument && fileName == other.fileName && content.contentEquals(other.content))
+
+    override fun hashCode(): Int = 31 * fileName.hashCode() + content.contentHashCode()
+}

app/src/main/java/de/jeanlucmakiola/agendula/domain/export/ICalendarWriter.kt

@@ -0,0 +1,204 @@
+package de.jeanlucmakiola.agendula.domain.export
+
+import de.jeanlucmakiola.agendula.domain.Priority
+import de.jeanlucmakiola.agendula.domain.TaskStatus
+import de.jeanlucmakiola.agendula.domain.calendarDate
+import de.jeanlucmakiola.agendula.domain.toICal
+import java.time.ZoneOffset
+import java.time.format.DateTimeFormatter
+import kotlin.time.Instant
+
+/**
+ * Writes a task list as an RFC 5545 `VCALENDAR` of `VTODO` components.
+ *
+ * Pure Kotlin and deliberately free of any Android type, so the format — the part
+ * that decides whether an exported backup can actually be read again — is
+ * unit-testable on the JVM. Serialising tasks is task-domain and stays here; the
+ * SAF/file plumbing that carries the bytes out is not, and lives in the data
+ * layer (and is the piece `docs/STORAGE-AND-SYNC.md` marks as a floret-kit
+ * candidate).
+ *
+ * **Times are always written in UTC.** Emitting a local `TZID` would oblige us to
+ * also emit a matching `VTIMEZONE` component with its full transition rules, and
+ * a `TZID` referencing an absent definition is what actually breaks importers. UTC
+ * is unambiguous and universally accepted, so the exported instant is exact even
+ * though the original wall-clock zone is not carried. All-day values keep their
+ * `VALUE=DATE` form and stay date-only, which is the only representation that
+ * survives a timezone change intact.
+ */
+object ICalendarWriter {
+
+    private const val PRODUCT_ID = "-//Jean-Luc Makiola//Agendula//EN"
+
+    /** RFC 5545 caps a content line at 75 octets, excluding the CRLF. */
+    private const val MAX_LINE_OCTETS = 75
+
+    private val DATE = DateTimeFormatter.ofPattern("yyyyMMdd")
+    private val DATE_TIME_UTC = DateTimeFormatter.ofPattern("yyyyMMdd'T'HHmmss'Z'")
+
+    /** Serialises [list] to a complete `.ics` document. */
+    fun write(list: ExportList): String = buildString {
+        line("BEGIN:VCALENDAR")
+        line("VERSION:2.0")
+        line("PRODID:$PRODUCT_ID")
+        line("CALSCALE:GREGORIAN")
+        // Non-standard but near-universally understood, and the only way the list's
+        // name survives into a calendar app. Importers that don't know it skip it.
+        property("X-WR-CALNAME", list.name)
+
+        // Parents must be addressable by UID, and a subtask may appear before its
+        // parent in the list, so resolve every id up front.
+        val uidsById = list.tasks.associate { it.taskId to uidFor(it) }
+        list.tasks.forEach { task -> writeTask(task, uidsById) }
+
+        line("END:VCALENDAR")
+    }
+
+    /**
+     * The UID to write for [task].
+     *
+     * Local tasks have none, because nothing assigns one: the provider never
+     * generates a `_uid` itself, and our write path does not set it either, so in
+     * Local mode every task arrives here with `uid == null`.
+     *
+     * Note this is a gap we leave open, not one the provider imposes.
+     * `processors/tasks/Validating.java:92-96` restricts `_uid` to sync adapters
+     * on *update* only; `insert` does not check it, so any caller may assign a UID
+     * at creation. Doing that would be strictly better than synthesising here —
+     * see `docs/SYNC.md`, where it is a phase-1 item, because a real UID minted at
+     * creation is what lets a local task later be pushed to CalDAV without
+     * duplicating.
+     *
+     * Until then: a VTODO without a UID is invalid and, worse, un-mergeable —
+     * re-importing a backup would duplicate every task instead of matching it. So
+     * we synthesise one from the row id, which is stable for as long as the row
+     * is, and tag it with our own domain so a synthesised UID is recognisable as
+     * such.
+     */
+    fun uidFor(task: ExportTask): String =
+        task.uid?.takeIf { it.isNotBlank() } ?: "agendula-${task.taskId}@jeanlucmakiola.de"
+
+    private fun StringBuilder.writeTask(task: ExportTask, uidsById: Map<Long, String>) {
+        line("BEGIN:VTODO")
+        property("UID", uidFor(task))
+        // DTSTAMP is mandatory. It means "when this representation was written",
+        // which for an export is now — not the task's own timestamps.
+        property("DTSTAMP", formatUtc(Instant.fromEpochMilliseconds(System.currentTimeMillis())))
+        property("SUMMARY", task.title)
+
+        task.description?.takeIf { it.isNotBlank() }?.let { property("DESCRIPTION", it) }
+        task.location?.takeIf { it.isNotBlank() }?.let { property("LOCATION", it) }
+        // URL is a URI, not TEXT: it must not be escaped like one.
+        task.url?.takeIf { it.isNotBlank() }?.let { rawProperty("URL", it) }
+
+        task.start?.let { dateProperty("DTSTART", it, task.isAllDay) }
+        task.due?.let { dateProperty("DUE", it, task.isAllDay) }
+        task.created?.let { rawProperty("CREATED", formatUtc(it)) }
+        task.lastModified?.let { rawProperty("LAST-MODIFIED", formatUtc(it)) }
+        // COMPLETED is defined as UTC date-time even for an all-day task.
+        task.completedAt?.let { rawProperty("COMPLETED", formatUtc(it)) }
+
+        rawProperty("STATUS", task.status.toICalName())
+        if (task.priority != Priority.NONE) rawProperty("PRIORITY", task.priority.toICal().toString())
+        task.percentComplete?.coerceIn(0, 100)?.let { rawProperty("PERCENT-COMPLETE", it.toString()) }
+
+        // Passed through as stored. The provider keeps these in iCalendar form
+        // already, and re-deriving them would risk changing what the user's
+        // recurrence actually means.
+        task.rrule?.takeIf { it.isNotBlank() }?.let { rawProperty("RRULE", it) }
+        task.rdate?.takeIf { it.isNotBlank() }?.let { rawProperty("RDATE", it) }
+
+        // Only emit the link when the parent is in this same document; a
+        // RELATED-TO pointing outside the file would dangle on import.
+        task.parentId?.let { uidsById[it] }?.let {
+            property("RELATED-TO;RELTYPE=PARENT", it)
+        }
+
+        line("END:VTODO")
+    }
+
+    private fun StringBuilder.dateProperty(name: String, instant: Instant, allDay: Boolean) {
+        if (allDay) {
+            // Read in UTC, matching the storage convention (see AllDayTime): an
+            // all-day value *is* UTC midnight of the intended calendar date.
+            rawProperty("$name;VALUE=DATE", instant.calendarDate(allDay = true).format(DATE))
+        } else {
+            rawProperty(name, formatUtc(instant))
+        }
+    }
+
+    private fun formatUtc(instant: Instant): String =
+        java.time.Instant.ofEpochMilli(instant.toEpochMilliseconds())
+            .atZone(ZoneOffset.UTC)
+            .format(DATE_TIME_UTC)
+
+    /** A property whose value is TEXT, and so must be escaped. */
+    private fun StringBuilder.property(name: String, value: String) =
+        line("$name:${escapeText(value)}")
+
+    /** A property whose value is already in its final form (dates, numbers, URIs, rules). */
+    private fun StringBuilder.rawProperty(name: String, value: String) = line("$name:$value")
+
+    private fun StringBuilder.line(content: String) {
+        append(fold(content))
+        append(CRLF)
+    }
+
+    /**
+     * Escapes a TEXT value per RFC 5545 §3.3.11. Backslash first, or it would
+     * double the backslashes introduced by the later replacements.
+     */
+    internal fun escapeText(value: String): String = value
+        .replace("\\", "\\\\")
+        .replace(";", "\\;")
+        .replace(",", "\\,")
+        .replace("\r\n", "\\n")
+        .replace("\n", "\\n")
+        .replace("\r", "\\n")
+
+    /**
+     * Folds a content line to at most [MAX_LINE_OCTETS] octets, continuing with
+     * CRLF + a single space.
+     *
+     * Counted in **octets, not characters** — the limit is defined that way, and an
+     * emoji in a task title is four of them. Splits are kept on character
+     * boundaries so folding can never cut a UTF-8 sequence in half and corrupt the
+     * text; an importer unfolds by removing CRLF + leading whitespace, recovering
+     * the original exactly.
+     */
+    internal fun fold(content: String): String {
+        if (content.utf8Size() <= MAX_LINE_OCTETS) return content
+
+        val out = StringBuilder()
+        var octets = 0
+        // First line takes the full budget; every continuation loses one octet to
+        // the leading space.
+        var budget = MAX_LINE_OCTETS
+        var index = 0
+        while (index < content.length) {
+            val codePoint = content.codePointAt(index)
+            val charCount = Character.charCount(codePoint)
+            val size = String(Character.toChars(codePoint)).utf8Size()
+            if (octets + size > budget) {
+                out.append(CRLF).append(' ')
+                octets = 0
+                budget = MAX_LINE_OCTETS - 1
+            }
+            out.append(content, index, index + charCount)
+            octets += size
+            index += charCount
+        }
+        return out.toString()
+    }
+
+    private fun String.utf8Size(): Int = toByteArray(Charsets.UTF_8).size
+
+    private fun TaskStatus.toICalName(): String = when (this) {
+        TaskStatus.NEEDS_ACTION -> "NEEDS-ACTION"
+        TaskStatus.IN_PROCESS -> "IN-PROCESS"
+        TaskStatus.COMPLETED -> "COMPLETED"
+        TaskStatus.CANCELLED -> "CANCELLED"
+    }
+
+    private const val CRLF = "\r\n"
+}

app/src/main/java/de/jeanlucmakiola/agendula/domain/recurrence/RecurrenceExpander.kt

@@ -0,0 +1,179 @@
+package de.jeanlucmakiola.agendula.domain.recurrence
+
+import org.dmfs.rfc5545.DateTime
+import org.dmfs.rfc5545.recur.RecurrenceRule
+import org.dmfs.rfc5545.recurrenceset.RecurrenceList
+import org.dmfs.rfc5545.recurrenceset.RecurrenceRuleAdapter
+import org.dmfs.rfc5545.recurrenceset.RecurrenceSet
+import java.time.ZoneId
+import java.util.TimeZone
+import kotlin.time.Instant
+
+private const val MILLIS_PER_SECOND = 1000L
+private const val MILLIS_PER_DAY = 24L * 60 * 60 * 1000
+
+/** The rule set of one task series, as stored. All strings are raw iCalendar values. */
+data class RecurrenceSpec(
+    val rrule: String?,
+    val rdate: String?,
+    val exdate: String?,
+    /** The series anchor: DTSTART if present, else DUE. Never null for a recurring task. */
+    val anchor: Instant,
+    val isAllDay: Boolean,
+    /** IANA zone id the anchor is expressed in; null means floating/local. */
+    val timeZone: String?,
+)
+
+/**
+ * The window expansion is bounded to: [from] inclusive, [until] exclusive, and
+ * never more than [maxOccurrences] results — so an unbounded `RRULE` terminates.
+ *
+ * [pivot] is where "now" sits inside the window, and it is what the occurrence
+ * budget is spent around. Without it a series firing more often than about
+ * once a day exhausts [maxOccurrences] inside the past alone — an eight-hourly
+ * task would stop expanding months before today, so it would never appear in
+ * Today or Upcoming at all. At most a quarter of the budget goes to occurrences
+ * before [pivot], and the most recent of those are the ones kept.
+ */
+data class ExpansionWindow(
+    val from: Instant,
+    val until: Instant,
+    val maxOccurrences: Int = 500,
+    val pivot: Instant = from,
+)
+
+/**
+ * Expands a task series into its occurrences in memory, over `lib-recur`.
+ *
+ * There is no materialised instances table behind this: the repository already
+ * filters and sorts in Kotlin, so occurrences are computed at read time and the
+ * whole class of staleness bugs a cached table brings never exists.
+ */
+object RecurrenceExpander {
+
+    /**
+     * Every occurrence of [spec] inside [window], as its `RECURRENCE-ID` anchor —
+     * the instant identifying that occurrence within the series. Ascending,
+     * deduplicated, `EXDATE` applied.
+     *
+     * The anchor itself is always part of the set (RFC 5545 §3.8.5.3: `DTSTART`
+     * is the first instance), so a spec with no rule and no `RDATE` expands to
+     * exactly its anchor. A malformed `RRULE`, `RDATE` or `EXDATE` is dropped
+     * rather than thrown — a task whose stored rule cannot be parsed still has
+     * to appear.
+     *
+     * [floatingZone] resolves a series with no [RecurrenceSpec.timeZone]; it is a
+     * parameter rather than a `TimeZone.getDefault()` lookup so expansion is
+     * deterministic under test.
+     */
+    fun expand(
+        spec: RecurrenceSpec,
+        window: ExpansionWindow,
+        floatingZone: ZoneId = ZoneId.systemDefault(),
+    ): List<Instant> {
+        val zone = zoneOf(spec, floatingZone)
+        val anchorMillis = anchorMillis(spec)
+
+        val set = RecurrenceSet()
+        spec.rrule.orNull()?.let { raw -> ruleOf(raw, zone)?.let { set.addInstances(RecurrenceRuleAdapter(it)) } }
+        spec.rdate.orNull()?.let { raw -> datesOf(raw, zone)?.let(set::addInstances) }
+        spec.exdate.orNull()?.let { raw -> datesOf(raw, zone)?.let(set::addExceptions) }
+
+        val iterator = set.iterator(zone, anchorMillis, window.until.toEpochMilliseconds())
+        iterator.fastForward(window.from.toEpochMilliseconds())
+
+        // Occurrences arrive ascending, so everything before the pivot lands first
+        // and `past` is final by the time the first future one appears. Past is a
+        // sliding window (the newest are the ones worth keeping); the rest of the
+        // budget then goes to the future, undiminished when there is no past.
+        val pastCap = window.maxOccurrences / 4
+        val past = ArrayDeque<Instant>()
+        val future = ArrayList<Instant>()
+        var previous = Long.MIN_VALUE
+        while (iterator.hasNext()) {
+            val millis = iterator.next()
+            if (millis == previous) continue
+            previous = millis
+            val at = Instant.fromEpochMilliseconds(millis)
+            if (at < window.pivot) {
+                if (past.size == pastCap) past.removeFirst()
+                if (pastCap > 0) past.addLast(at)
+            } else {
+                future += at
+                if (past.size + future.size >= window.maxOccurrences) break
+            }
+        }
+        return past + future
+    }
+
+    /**
+     * Index of the current occurrence in an ascending [occurrences] list: the
+     * first one at or after [now], or the last one when the whole series is in
+     * the past. `-1` when there are no occurrences at all.
+     */
+    fun currentOccurrenceIndex(occurrences: List<Instant>, now: Instant): Int {
+        if (occurrences.isEmpty()) return -1
+        val next = occurrences.indexOfFirst { it >= now }
+        return if (next >= 0) next else occurrences.lastIndex
+    }
+
+    /**
+     * Each occurrence's distance from the current one, index-aligned with
+     * [occurrences]. `0` is the current occurrence, negative counts back into the
+     * past and positive counts forward — the convention `Task.distanceFromCurrent`
+     * carries and the data sources pick the current occurrence by.
+     *
+     * Purely positional: unlike the dmfs provider, which drove the same number off
+     * each instance's closed state, this knows only times. Completion-aware
+     * refinement belongs where overrides carry their status.
+     */
+    fun distancesFromCurrent(occurrences: List<Instant>, now: Instant): List<Int> {
+        val current = currentOccurrenceIndex(occurrences, now)
+        if (current < 0) return emptyList()
+        return occurrences.indices.map { it - current }
+    }
+
+    private fun zoneOf(spec: RecurrenceSpec, floatingZone: ZoneId): TimeZone {
+        if (spec.isAllDay) return TimeZone.getTimeZone(ZoneId.of("UTC"))
+        val stored = spec.timeZone?.let { runCatching { ZoneId.of(it) }.getOrNull() }
+        return TimeZone.getTimeZone(stored ?: floatingZone)
+    }
+
+    /**
+     * All-day series are date-anchored: pin the anchor to UTC midnight, as it is
+     * stored. A timed one is floored to the second, because RFC 5545 DATE-TIME
+     * has no sub-second field — carrying millis in makes lib-recur emit the raw
+     * anchor *and* its truncated self, doubling the first occurrence, and mints
+     * `RECURRENCE-ID`s no other client could address.
+     */
+    private fun anchorMillis(spec: RecurrenceSpec): Long {
+        val millis = spec.anchor.toEpochMilliseconds()
+        val unit = if (spec.isAllDay) MILLIS_PER_DAY else MILLIS_PER_SECOND
+        return Math.floorDiv(millis, unit) * unit
+    }
+
+    private fun ruleOf(value: String, zone: TimeZone): RecurrenceRule? = runCatching {
+        RecurrenceRule(value).also { rule ->
+            // lib-recur refuses to iterate a floating UNTIL against a zoned start,
+            // and RFC 5545 §3.3.10 forbids that pairing — but stored rules carry it
+            // anyway. Re-read the UNTIL's local fields in the series zone.
+            val until = rule.until
+            if (until != null && until.isFloating) {
+                rule.until = DateTime(
+                    zone,
+                    until.year,
+                    until.month,
+                    until.dayOfMonth,
+                    until.hours,
+                    until.minutes,
+                    until.seconds,
+                )
+            }
+        }
+    }.getOrNull()
+
+    private fun datesOf(value: String, zone: TimeZone): RecurrenceList? =
+        runCatching { RecurrenceList(value, zone) }.getOrNull()
+
+    private fun String?.orNull(): String? = this?.trim()?.ifEmpty { null }
+}

app/src/main/java/de/jeanlucmakiola/agendula/ui/RootScreen.kt

@@ -10,6 +10,7 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.material3.Button
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.ui.Alignment
@@ -19,6 +20,7 @@ import androidx.compose.ui.unit.dp
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.jeanlucmakiola.agendula.R
+import de.jeanlucmakiola.agendula.ui.common.OnResume
 import de.jeanlucmakiola.agendula.data.tasks.ProviderStatus
 import de.jeanlucmakiola.agendula.ui.navigation.AgendulaNavHost
 import de.jeanlucmakiola.agendula.ui.permission.PermissionViewModel
@@ -39,11 +41,23 @@ fun RootScreen(
         ActivityResultContracts.RequestMultiplePermissions(),
     ) { permissionViewModel.refresh() }
 
+    // Re-check on every resume, not just after the in-app request: the user may
+    // have granted the permission (or installed a provider) in system Settings and
+    // come back, and otherwise the gate would hold until the process restarts.
+    OnResume { permissionViewModel.refresh() }
+
+    // Neither gate can show in OWN mode (that store is always READY), so the way
+    // out of one is always our own store. Without it a user whose provider app
+    // went away is held on this screen with Settings behind it.
+    val fallback = stringResource(R.string.onboarding_use_own_store)
+
     when (permission.status) {
         ProviderStatus.NO_PROVIDER -> Gate(
             modifier = modifier,
             title = stringResource(R.string.onboarding_no_provider_title),
             body = stringResource(R.string.onboarding_no_provider_body),
+            secondaryAction = fallback,
+            onSecondaryAction = permissionViewModel::useOwnStore,
         )
         ProviderStatus.NEEDS_PERMISSION -> Gate(
             modifier = modifier,
@@ -51,6 +65,8 @@ fun RootScreen(
             body = stringResource(R.string.onboarding_permission_body),
             action = stringResource(R.string.onboarding_permission_button),
             onAction = { launcher.launch(permission.permissionsToRequest.toTypedArray()) },
+            secondaryAction = fallback,
+            onSecondaryAction = permissionViewModel::useOwnStore,
         )
         ProviderStatus.READY -> ReadyGate(modifier = modifier)
     }
@@ -87,6 +103,8 @@ private fun Gate(
     modifier: Modifier = Modifier,
     action: String? = null,
     onAction: () -> Unit = {},
+    secondaryAction: String? = null,
+    onSecondaryAction: () -> Unit = {},
 ) {
     Column(
         modifier = modifier.fillMaxSize().padding(24.dp),
@@ -96,5 +114,6 @@ private fun Gate(
         Text(title, style = MaterialTheme.typography.headlineSmall)
         Text(body, style = MaterialTheme.typography.bodyMedium)
         if (action != null) Button(onClick = onAction) { Text(action) }
+        if (secondaryAction != null) TextButton(onClick = onSecondaryAction) { Text(secondaryAction) }
     }
 }

app/src/main/java/de/jeanlucmakiola/agendula/ui/common/DateTimeField.kt

@@ -1,167 +0,0 @@
-package de.jeanlucmakiola.agendula.ui.common
-
-import de.jeanlucmakiola.floret.time.formatDateTime
-import androidx.compose.foundation.layout.Arrangement
-import androidx.compose.foundation.layout.Column
-import androidx.compose.foundation.layout.Row
-import androidx.compose.foundation.layout.fillMaxWidth
-import androidx.compose.foundation.layout.padding
-import androidx.compose.foundation.shape.RoundedCornerShape
-import androidx.compose.material.icons.Icons
-import androidx.compose.material.icons.rounded.Clear
-import androidx.compose.material.icons.rounded.Event
-import androidx.compose.material3.DatePicker
-import androidx.compose.material3.DatePickerDialog
-import androidx.compose.material3.ExperimentalMaterial3Api
-import androidx.compose.material3.Icon
-import androidx.compose.material3.IconButton
-import androidx.compose.material3.MaterialTheme
-import androidx.compose.material3.Surface
-import androidx.compose.material3.Text
-import androidx.compose.material3.TextButton
-import androidx.compose.material3.TimePicker
-import androidx.compose.material3.rememberDatePickerState
-import androidx.compose.material3.rememberTimePickerState
-import androidx.compose.runtime.Composable
-import androidx.compose.runtime.getValue
-import androidx.compose.runtime.mutableStateOf
-import androidx.compose.runtime.remember
-import androidx.compose.runtime.setValue
-import androidx.compose.ui.Alignment
-import androidx.compose.ui.Modifier
-import androidx.compose.ui.res.stringResource
-import androidx.compose.ui.unit.dp
-import androidx.compose.ui.window.Dialog
-import de.jeanlucmakiola.agendula.R
-import java.time.LocalDate
-import java.time.LocalTime
-import java.time.ZoneId
-import java.time.ZoneOffset
-import kotlin.time.Instant
-
-private val zone: ZoneId get() = ZoneId.systemDefault()
-
-internal fun Instant.toLocalDate(): LocalDate =
-    java.time.Instant.ofEpochMilli(toEpochMilliseconds()).atZone(zone).toLocalDate()
-
-internal fun Instant.toLocalTime(): LocalTime =
-    java.time.Instant.ofEpochMilli(toEpochMilliseconds()).atZone(zone).toLocalTime()
-
-internal fun localToInstant(date: LocalDate, time: LocalTime): Instant =
-    Instant.fromEpochMilliseconds(date.atTime(time).atZone(zone).toInstant().toEpochMilli())
-
-/**
- * A labelled date(-time) field for the edit form: a tonal row showing the
- * current value (or nothing), tappable to pick a date and — unless [allDay] —
- * a time. A clear affordance appears once a value is set. Emits `null` when
- * cleared. Styled to match the app's rounded tonal family.
- */
-@OptIn(ExperimentalMaterial3Api::class)
-@Composable
-fun DateTimeField(
-    label: String,
-    value: Instant?,
-    allDay: Boolean,
-    onChange: (Instant?) -> Unit,
-    modifier: Modifier = Modifier,
-) {
-    var showDatePicker by remember { mutableStateOf(false) }
-    var showTimePicker by remember { mutableStateOf(false) }
-    var pendingDate by remember { mutableStateOf<LocalDate?>(null) }
-
-    Surface(
-        onClick = { showDatePicker = true },
-        shape = RoundedCornerShape(22.dp),
-        color = MaterialTheme.colorScheme.surfaceContainerHigh,
-        modifier = modifier.fillMaxWidth(),
-    ) {
-        Row(
-            modifier = Modifier.padding(horizontal = 20.dp, vertical = 14.dp),
-            verticalAlignment = Alignment.CenterVertically,
-            horizontalArrangement = Arrangement.spacedBy(12.dp),
-        ) {
-            Icon(Icons.Rounded.Event, contentDescription = null, tint = MaterialTheme.colorScheme.onSurfaceVariant)
-            Column(modifier = Modifier.weight(1f)) {
-                Text(
-                    text = label,
-                    style = MaterialTheme.typography.labelMedium,
-                    color = MaterialTheme.colorScheme.onSurfaceVariant,
-                )
-                Text(
-                    text = value?.formatDateTime(allDay) ?: stringResource(R.string.edit_set),
-                    style = MaterialTheme.typography.bodyLarge,
-                )
-            }
-            if (value != null) {
-                IconButton(onClick = { onChange(null) }) {
-                    Icon(Icons.Rounded.Clear, contentDescription = stringResource(R.string.edit_clear))
-                }
-            }
-        }
-    }
-
-    if (showDatePicker) {
-        val initialMillis = (value ?: Instant.fromEpochMilliseconds(System.currentTimeMillis()))
-            .toLocalDate().atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli()
-        val dateState = rememberDatePickerState(initialSelectedDateMillis = initialMillis)
-        DatePickerDialog(
-            onDismissRequest = { showDatePicker = false },
-            confirmButton = {
-                TextButton(
-                    onClick = {
-                        showDatePicker = false
-                        val millis = dateState.selectedDateMillis ?: return@TextButton
-                        val date = java.time.Instant.ofEpochMilli(millis)
-                            .atZone(ZoneOffset.UTC).toLocalDate()
-                        if (allDay) {
-                            onChange(localToInstant(date, LocalTime.MIDNIGHT))
-                        } else {
-                            pendingDate = date
-                            showTimePicker = true
-                        }
-                    },
-                ) { Text(stringResource(android.R.string.ok)) }
-            },
-            dismissButton = {
-                TextButton(onClick = { showDatePicker = false }) {
-                    Text(stringResource(android.R.string.cancel))
-                }
-            },
-        ) { DatePicker(state = dateState) }
-    }
-
-    if (showTimePicker) {
-        val base = value ?: Instant.fromEpochMilliseconds(System.currentTimeMillis())
-        val timeState = rememberTimePickerState(
-            initialHour = base.toLocalTime().hour,
-            initialMinute = base.toLocalTime().minute,
-        )
-        Dialog(onDismissRequest = { showTimePicker = false }) {
-            Surface(
-                shape = RoundedCornerShape(28.dp),
-                color = MaterialTheme.colorScheme.surfaceContainerHigh,
-            ) {
-                Column(
-                    modifier = Modifier.padding(24.dp),
-                    horizontalAlignment = Alignment.CenterHorizontally,
-                    verticalArrangement = Arrangement.spacedBy(16.dp),
-                ) {
-                    TimePicker(state = timeState)
-                    Row(
-                        modifier = Modifier.fillMaxWidth(),
-                        horizontalArrangement = Arrangement.End,
-                    ) {
-                        TextButton(onClick = { showTimePicker = false }) {
-                            Text(stringResource(android.R.string.cancel))
-                        }
-                        TextButton(onClick = {
-                            showTimePicker = false
-                            val date = pendingDate ?: return@TextButton
-                            onChange(localToInstant(date, LocalTime.of(timeState.hour, timeState.minute)))
-                        }) { Text(stringResource(android.R.string.ok)) }
-                    }
-                }
-            }
-        }
-    }
-}

app/src/main/java/de/jeanlucmakiola/agendula/ui/common/ListColors.kt

@@ -0,0 +1,29 @@
+package de.jeanlucmakiola.agendula.ui.common
+
+/**
+ * The colours offered when creating or editing a task list.
+ *
+ * Raw ARGB, the way a CalDAV server sends one — every surface that draws a list
+ * colour runs it through
+ * [de.jeanlucmakiola.floret.components.pastelize] first, so these are hues
+ * rather than final fills, chosen to stay distinguishable after that pass. A
+ * list can still carry any colour a server gives it; this is only the set the
+ * app hands out.
+ */
+val ListPalette: List<Int> = listOf(
+    0xFF7A5C6B.toInt(), // mauve — Agendula's own seed
+    0xFFD7484A.toInt(), // red
+    0xFFE8743B.toInt(), // orange
+    0xFFE0A32E.toInt(), // amber
+    0xFF7CA83E.toInt(), // olive
+    0xFF35A06A.toInt(), // green
+    0xFF19938C.toInt(), // teal
+    0xFF2A9BC4.toInt(), // cyan
+    0xFF3C74C8.toInt(), // blue
+    0xFF6A5CC0.toInt(), // indigo
+    0xFF9455B8.toInt(), // purple
+    0xFFC94F8E.toInt(), // pink
+)
+
+/** What a new list gets before the user picks anything. */
+val DefaultListColor: Int = ListPalette.first()

app/src/main/java/de/jeanlucmakiola/agendula/ui/common/OnResume.kt

@@ -0,0 +1,29 @@
+package de.jeanlucmakiola.agendula.ui.common
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisposableEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.rememberUpdatedState
+import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.LifecycleEventObserver
+import androidx.lifecycle.compose.LocalLifecycleOwner
+
+/**
+ * Runs [block] on every `ON_RESUME`.
+ *
+ * For state the app cannot observe because it is granted, revoked or installed
+ * outside it — a runtime permission, an exact-alarm allowance, a provider app —
+ * which otherwise stays stale until the process restarts.
+ */
+@Composable
+fun OnResume(block: () -> Unit) {
+    val current by rememberUpdatedState(block)
+    val lifecycle = LocalLifecycleOwner.current.lifecycle
+    DisposableEffect(lifecycle) {
+        val observer = LifecycleEventObserver { _, event ->
+            if (event == Lifecycle.Event.ON_RESUME) current()
+        }
+        lifecycle.addObserver(observer)
+        onDispose { lifecycle.removeObserver(observer) }
+    }
+}

app/src/main/java/de/jeanlucmakiola/agendula/ui/common/PickerTime.kt

@@ -0,0 +1,20 @@
+package de.jeanlucmakiola.agendula.ui.common
+
+import java.time.LocalDate
+import java.time.LocalTime
+import java.time.ZoneId
+import kotlin.time.Instant
+
+/**
+ * Zone helpers shared by the date/time pickers. All-day conversions live in
+ * [de.jeanlucmakiola.agendula.domain.AllDayTime] — these cover the timed case,
+ * where the device zone is the right frame of reference.
+ */
+
+private val zone: ZoneId get() = ZoneId.systemDefault()
+
+internal fun Instant.toLocalTime(): LocalTime =
+    java.time.Instant.ofEpochMilli(toEpochMilliseconds()).atZone(zone).toLocalTime()
+
+internal fun localToInstant(date: LocalDate, time: LocalTime): Instant =
+    Instant.fromEpochMilliseconds(date.atTime(time).atZone(zone).toInstant().toEpochMilli())

app/src/main/java/de/jeanlucmakiola/agendula/ui/common/ReminderLeadPicker.kt

@@ -54,7 +54,9 @@ fun ReminderLeadPicker(
     onDismiss: () -> Unit,
     presets: List<Int> = REMINDER_PRESETS,
 ) {
-    val selectedMinutes = (selected as? ReminderOverride.Minutes)?.minutes
+    // Agendula is single-reminder: an override carries a one-element list, so
+    // take the single value for this single-select picker.
+    val selectedMinutes = (selected as? ReminderOverride.Minutes)?.minutes?.firstOrNull()
     val customSelected = selectedMinutes != null && selectedMinutes !in presets
     val seed = decomposeReminderMinutes(selectedMinutes?.takeIf { customSelected })
 
@@ -65,7 +67,7 @@ fun ReminderLeadPicker(
     val options = buildList {
         if (allowInherit) add(ReminderOverride.Inherit)
         if (allowNone) add(ReminderOverride.None)
-        presets.forEach { add(ReminderOverride.Minutes(it)) }
+        presets.forEach { add(ReminderOverride.Minutes(listOf(it))) }
     }
     val rowCount = options.size + 1 // + the custom row
 
@@ -105,7 +107,7 @@ fun ReminderLeadPicker(
                 unit = unit,
                 onUnitChange = { unit = it },
                 onConfirm = { minutes ->
-                    onSelect(ReminderOverride.Minutes(minutes))
+                    onSelect(ReminderOverride.Minutes(listOf(minutes)))
                     onDismiss()
                 },
             )
@@ -168,5 +170,5 @@ private fun CustomReminderEditor(
 private fun reminderOverrideLabel(override: ReminderOverride): String = when (override) {
     ReminderOverride.Inherit -> stringResource(R.string.reminder_use_default)
     ReminderOverride.None -> stringResource(R.string.reminder_none)
-    is ReminderOverride.Minutes -> reminderLeadTimeLabel(override.minutes)
+    is ReminderOverride.Minutes -> reminderLeadTimeLabel(override.minutes.first())
 }

app/src/main/java/de/jeanlucmakiola/agendula/ui/common/ShapedActionButton.kt

@@ -98,4 +98,7 @@ object ActionShapes {
 
     /** Search — a 6-sided cookie, the same family as [Settings] but distinct. */
     val Search: RoundedPolygon get() = MaterialShapes.Cookie6Sided
+
+    /** New list — a sunny burst beside the Lists header. */
+    val AddList: RoundedPolygon get() = MaterialShapes.Sunny
 }

app/src/main/java/de/jeanlucmakiola/agendula/ui/detail/TaskDetailScreen.kt

@@ -501,13 +501,17 @@ private fun taskWhenLines(task: Task): Pair<String, String?>? {
     val due = task.due
     return when {
         start != null && due != null -> {
-            val sameDay = start.formatDate() == due.formatDate()
-            val primary = if (sameDay) due.formatDate() else "${start.formatDate()} – ${due.formatDate()}"
-            val secondary = if (task.isAllDay) null else "${start.formatTime()} – ${due.formatTime()}"
+            val allDay = task.isAllDay
+            val sameDay = start.formatDate(allDay) == due.formatDate(allDay)
+            val primary =
+                if (sameDay) due.formatDate(allDay)
+                else "${start.formatDate(allDay)} – ${due.formatDate(allDay)}"
+            val secondary = if (allDay) null else "${start.formatTime()} – ${due.formatTime()}"
             primary to secondary
         }
-        due != null -> due.formatDate() to if (task.isAllDay) null else due.formatTime()
-        start != null -> start.formatDate() to if (task.isAllDay) null else start.formatTime()
+        due != null -> due.formatDate(task.isAllDay) to if (task.isAllDay) null else due.formatTime()
+        start != null ->
+            start.formatDate(task.isAllDay) to if (task.isAllDay) null else start.formatTime()
         else -> null
     }
 }

app/src/main/java/de/jeanlucmakiola/agendula/ui/detail/TaskDetailViewModel.kt

@@ -4,6 +4,7 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
 import de.jeanlucmakiola.agendula.data.tasks.TasksRepository
+import de.jeanlucmakiola.agendula.data.tasks.recoveringFromProviderFailure
 import de.jeanlucmakiola.agendula.domain.Task
 import de.jeanlucmakiola.agendula.domain.TaskDetail
 import de.jeanlucmakiola.agendula.domain.TaskForm
@@ -11,7 +12,6 @@ import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
-import kotlinx.coroutines.flow.catch
 import kotlinx.coroutines.flow.filterNotNull
 import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.map
@@ -42,14 +42,14 @@ class TaskDetailViewModel @Inject constructor(
                         if (detail == null) TaskDetailUiState.NotFound else TaskDetailUiState.Content(detail)
                     }
                     .onStart { emit(TaskDetailUiState.Loading) }
-                    .catch { emit(TaskDetailUiState.NotFound) }
+                    .recoveringFromProviderFailure { TaskDetailUiState.NotFound }
             }
             .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), TaskDetailUiState.Loading)
 
     fun bind(id: Long) { taskId.value = id }
 
     fun toggleComplete(task: Task) = viewModelScope.launch {
-        runCatching { repository.setCompleted(task.taskId, !task.isCompleted) }
+        runCatching { repository.setCompleted(task.taskId, task.occurrenceStart, !task.isCompleted) }
     }
 
     fun delete(task: Task) = viewModelScope.launch {

app/src/main/java/de/jeanlucmakiola/agendula/ui/edit/TaskEditScreen.kt

@@ -99,7 +99,8 @@ import de.jeanlucmakiola.floret.time.formatTime
 import de.jeanlucmakiola.agendula.ui.common.localToInstant
 import de.jeanlucmakiola.floret.components.pastelize
 import de.jeanlucmakiola.floret.components.positionOf
-import de.jeanlucmakiola.agendula.ui.common.toLocalDate
+import de.jeanlucmakiola.agendula.domain.allDayInstantOf
+import de.jeanlucmakiola.agendula.domain.calendarDate
 import de.jeanlucmakiola.agendula.ui.common.toLocalTime
 import de.jeanlucmakiola.agendula.ui.tasklist.priorityLabel
 import java.time.LocalTime
@@ -178,7 +179,7 @@ private fun EditContent(
     val accent = selectedList?.let { pastelize(it.color, dark) } ?: MaterialTheme.colorScheme.primary
     val gap = 12.dp
 
-    var pickerTarget by remember { mutableStateOf<PickerTarget?>(null) }
+    var pickerTarget by rememberSaveable { mutableStateOf<PickerTarget?>(null) }
     var showListPicker by rememberSaveable { mutableStateOf(false) }
     var showParentPicker by rememberSaveable { mutableStateOf(false) }
     var showReminderPicker by rememberSaveable { mutableStateOf(false) }
@@ -653,7 +654,7 @@ private fun ScheduleRow(
             )
         } else {
             Text(
-                text = value.formatDate(),
+                text = value.formatDate(allDay),
                 style = MaterialTheme.typography.titleMedium,
                 color = valueColor,
                 modifier = Modifier.clickable(onClick = onPick).padding(vertical = 8.dp, horizontal = 6.dp),
@@ -689,12 +690,15 @@ private fun DateTimePickerFlow(
     onResult: (Instant) -> Unit,
     onDismiss: () -> Unit,
 ) {
-    var pendingDate by remember { mutableStateOf<java.time.LocalDate?>(null) }
-    var showTime by remember { mutableStateOf(false) }
+    var pendingDate by rememberSaveable { mutableStateOf<java.time.LocalDate?>(null) }
+    var showTime by rememberSaveable { mutableStateOf(false) }
 
     if (!showTime) {
+        // M3's DatePicker speaks UTC millis. An all-day value is already UTC-based,
+        // a timed one is read in the device zone — calendarDate picks the right frame
+        // so the dialog opens on the day the rest of the UI shows.
         val initialMillis = (initial ?: nowInstant())
-            .toLocalDate().atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli()
+            .calendarDate(allDay).atStartOfDay(ZoneOffset.UTC).toInstant().toEpochMilli()
         val dateState = rememberDatePickerState(initialSelectedDateMillis = initialMillis)
         DatePickerDialog(
             onDismissRequest = onDismiss,
@@ -703,7 +707,7 @@ private fun DateTimePickerFlow(
                     val millis = dateState.selectedDateMillis ?: run { onDismiss(); return@TextButton }
                     val date = java.time.Instant.ofEpochMilli(millis).atZone(ZoneOffset.UTC).toLocalDate()
                     if (allDay) {
-                        onResult(localToInstant(date, LocalTime.MIDNIGHT))
+                        onResult(allDayInstantOf(date))
                     } else {
                         pendingDate = date
                         showTime = true
@@ -865,7 +869,7 @@ private fun ParentPickerSheet(
                     GroupedRow(
                         title = task.title.ifBlank { stringResource(R.string.task_untitled) },
                         position = positionOf(index, section.tasks.size),
-                        summary = task.due?.formatDate(),
+                        summary = task.due?.formatDate(task.isAllDay),
                         selected = task.taskId == selectedId,
                         minHeight = 56.dp,
                         onClick = { choose(task.taskId) },

app/src/main/java/de/jeanlucmakiola/agendula/ui/edit/TaskEditViewModel.kt

@@ -15,6 +15,7 @@ import de.jeanlucmakiola.agendula.domain.TaskFormError
 import de.jeanlucmakiola.agendula.domain.TaskFormField
 import de.jeanlucmakiola.agendula.domain.TaskList
 import de.jeanlucmakiola.agendula.domain.populatedFields
+import de.jeanlucmakiola.agendula.domain.rebasedForAllDay
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
@@ -70,6 +71,15 @@ class TaskEditViewModel @Inject constructor(
 
     private var editingTaskId: Long? = null
 
+    /**
+     * Whether the form has already been populated. The host `LaunchedEffect`
+     * re-fires whenever the composition restarts — an Activity recreation
+     * (rotation, theme/font/display-size change, split-screen, unfolding) — while
+     * this ViewModel survives on the nav back stack. Without this guard the
+     * rebind would overwrite in-progress edits with the untouched provider row.
+     */
+    private var bound = false
+
     /** `last_modified` captured when the form loaded — the conflict-check baseline. */
     private var baselineLastModified: Instant? = null
 
@@ -78,6 +88,8 @@ class TaskEditViewModel @Inject constructor(
 
     /** Start a fresh task, optionally pre-selecting a list / parent. */
     fun bindNew(presetListId: Long? = null, parentId: Long? = null) {
+        if (bound) return
+        bound = true
         editingTaskId = null
         baselineLastModified = null
         viewModelScope.launch {
@@ -103,6 +115,8 @@ class TaskEditViewModel @Inject constructor(
 
     /** Load an existing task for editing. */
     fun bindEdit(taskId: Long) {
+        if (bound && editingTaskId == taskId) return
+        bound = true
         editingTaskId = taskId
         viewModelScope.launch {
             defaultFields = settingsPrefs.settings.first().defaultEditFields
@@ -126,6 +140,7 @@ class TaskEditViewModel @Inject constructor(
                     priority = task.priority,
                     parentId = task.parentId,
                     percentComplete = task.percentComplete,
+                    reminderMinutesBeforeDue = repository.reminderFor(taskId),
                     lists = lists,
                     parentCandidates = loadParents(task.listId, selfId = taskId),
                 ),
@@ -178,7 +193,19 @@ class TaskEditViewModel @Inject constructor(
 
     fun onStartChange(value: Instant?) = update { it.copy(start = value) }
     fun onDueChange(value: Instant?) = update { it.copy(due = value) }
-    fun onAllDayChange(value: Boolean) = update { it.copy(isAllDay = value) }
+    /**
+     * All-day and timed values use different conventions (UTC midnight vs. a real
+     * instant in the device zone), so the switch has to move the timestamps too —
+     * flipping the flag alone makes an all-day task read back as "02:00", which
+     * looks to the user like the time reset itself.
+     */
+    fun onAllDayChange(value: Boolean) = update {
+        it.copy(
+            isAllDay = value,
+            start = it.start?.rebasedForAllDay(value),
+            due = it.due?.rebasedForAllDay(value),
+        )
+    }
     fun onPriorityChange(value: Priority) = update { it.copy(priority = value) }
     fun onPercentChange(value: Int?) = update { it.copy(percentComplete = value?.coerceIn(0, 100)) }
     fun onParentChange(parentId: Long?) = update { it.copy(parentId = parentId) }

app/src/main/java/de/jeanlucmakiola/agendula/ui/export/ExportScreen.kt

@@ -0,0 +1,182 @@
+package de.jeanlucmakiola.agendula.ui.export
+
+import androidx.activity.compose.rememberLauncherForActivityResult
+import androidx.activity.result.contract.ActivityResultContracts
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.rounded.Circle
+import androidx.compose.material.icons.rounded.Folder
+import androidx.compose.material.icons.rounded.FolderZip
+import androidx.compose.material3.Button
+import androidx.compose.material3.Checkbox
+import androidx.compose.material3.CircularProgressIndicator
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedButton
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.res.pluralStringResource
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.unit.dp
+import androidx.hilt.navigation.compose.hiltViewModel
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import de.jeanlucmakiola.agendula.R
+import de.jeanlucmakiola.agendula.data.export.ExportFailure
+import de.jeanlucmakiola.floret.components.CollapsingScaffold
+import de.jeanlucmakiola.floret.components.GroupedRow
+import de.jeanlucmakiola.floret.components.Position
+import de.jeanlucmakiola.floret.components.pastelize
+import de.jeanlucmakiola.floret.components.positionOf
+
+private const val ZIP_MIME = "application/zip"
+private const val ZIP_NAME = "agendula-tasks.zip"
+
+/**
+ * Export the task lists as iCalendar. Which lists go out is a per-list tick; the
+ * destination is a folder or a single zip, both picked through SAF so the app
+ * needs no storage permission.
+ */
+@Composable
+fun ExportScreen(
+    onBack: () -> Unit,
+    modifier: Modifier = Modifier,
+    viewModel: ExportViewModel = hiltViewModel(),
+) {
+    val state by viewModel.state.collectAsStateWithLifecycle()
+    val dark = isSystemInDarkTheme()
+
+    val folderLauncher = rememberLauncherForActivityResult(
+        contract = ActivityResultContracts.OpenDocumentTree(),
+    ) { uri -> uri?.let(viewModel::exportToFolder) }
+    val zipLauncher = rememberLauncherForActivityResult(
+        contract = ActivityResultContracts.CreateDocument(ZIP_MIME),
+    ) { uri -> uri?.let(viewModel::exportToZip) }
+
+    val canExport = !state.running && state.selectedCount > 0
+
+    CollapsingScaffold(
+        title = stringResource(R.string.settings_export),
+        onBack = onBack,
+        modifier = modifier,
+    ) {
+        Text(
+            text = stringResource(R.string.export_hint),
+            style = MaterialTheme.typography.bodyMedium,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+            modifier = Modifier.padding(horizontal = 16.dp, vertical = 4.dp),
+        )
+        Spacer(Modifier.height(16.dp))
+
+        if (state.lists.isEmpty()) {
+            GroupedRow(
+                title = stringResource(R.string.export_no_lists),
+                position = Position.Alone,
+                dimmed = true,
+            )
+        } else {
+            state.lists.forEachIndexed { index, list ->
+                val selected = state.isSelected(list.id)
+                GroupedRow(
+                    title = list.name,
+                    // The account only says something when it isn't the device itself.
+                    summary = list.accountName.takeIf { !list.isLocal },
+                    position = positionOf(index, state.lists.size),
+                    leading = {
+                        Icon(Icons.Rounded.Circle, contentDescription = null, tint = pastelize(list.color, dark))
+                    },
+                    trailing = {
+                        Checkbox(checked = selected, onCheckedChange = { viewModel.toggle(list.id) })
+                    },
+                    onClick = { viewModel.toggle(list.id) },
+                )
+            }
+        }
+
+        Spacer(Modifier.height(24.dp))
+        Column(
+            modifier = Modifier.fillMaxWidth().padding(horizontal = 16.dp),
+            verticalArrangement = Arrangement.spacedBy(8.dp),
+        ) {
+            Button(
+                onClick = { folderLauncher.launch(null) },
+                enabled = canExport,
+                modifier = Modifier.fillMaxWidth(),
+            ) {
+                Icon(Icons.Rounded.Folder, contentDescription = null, modifier = Modifier.size(18.dp))
+                Spacer(Modifier.size(8.dp))
+                Text(stringResource(R.string.export_to_folder))
+            }
+            OutlinedButton(
+                onClick = { zipLauncher.launch(ZIP_NAME) },
+                enabled = canExport,
+                modifier = Modifier.fillMaxWidth(),
+            ) {
+                Icon(Icons.Rounded.FolderZip, contentDescription = null, modifier = Modifier.size(18.dp))
+                Spacer(Modifier.size(8.dp))
+                Text(stringResource(R.string.export_to_zip))
+            }
+        }
+
+        Spacer(Modifier.height(16.dp))
+        ExportStatus(state = state)
+        Spacer(Modifier.height(24.dp))
+    }
+}
+
+/** The running spinner, then whatever the last export ended as — it stays put. */
+@Composable
+private fun ExportStatus(state: ExportUiState) {
+    val outcome = state.outcome
+    when {
+        state.running -> Row(
+            modifier = Modifier.fillMaxWidth().padding(horizontal = 16.dp),
+            verticalAlignment = Alignment.CenterVertically,
+            horizontalArrangement = Arrangement.spacedBy(12.dp),
+        ) {
+            CircularProgressIndicator(Modifier.size(18.dp))
+            Text(
+                text = stringResource(R.string.export_running),
+                style = MaterialTheme.typography.bodyMedium,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+            )
+        }
+        outcome is ExportOutcome.Success -> StatusText(
+            text = pluralStringResource(R.plurals.export_done, outcome.fileCount, outcome.fileCount),
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+        )
+        outcome is ExportOutcome.Failure -> StatusText(
+            text = stringResource(failureMessage(outcome.reason)),
+            color = MaterialTheme.colorScheme.error,
+        )
+    }
+}
+
+private fun failureMessage(reason: ExportFailure): Int = when (reason) {
+    ExportFailure.FOLDER_UNAVAILABLE -> R.string.export_failed_folder
+    ExportFailure.FOLDER_NOT_WRITABLE -> R.string.export_failed_read_only
+    ExportFailure.CANNOT_CREATE_FILE -> R.string.export_failed_create
+    ExportFailure.LOST_ACCESS -> R.string.export_failed_access
+    ExportFailure.WRITE_FAILED -> R.string.export_failed
+}
+
+@Composable
+private fun StatusText(text: String, color: Color) {
+    Text(
+        text = text,
+        style = MaterialTheme.typography.bodyMedium,
+        color = color,
+        modifier = Modifier.fillMaxWidth().padding(horizontal = 16.dp),
+    )
+}

app/src/main/java/de/jeanlucmakiola/agendula/ui/export/ExportViewModel.kt

@@ -0,0 +1,122 @@
+package de.jeanlucmakiola.agendula.ui.export
+
+import android.net.Uri
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import dagger.hilt.android.lifecycle.HiltViewModel
+import de.jeanlucmakiola.agendula.data.export.ExportFailedException
+import de.jeanlucmakiola.agendula.data.export.ExportFailure
+import de.jeanlucmakiola.agendula.data.export.ExportResult
+import de.jeanlucmakiola.agendula.data.export.ExportWriter
+import de.jeanlucmakiola.agendula.data.export.TaskExporter
+import de.jeanlucmakiola.agendula.data.tasks.ProviderResolver
+import de.jeanlucmakiola.agendula.data.tasks.TasksRepository
+import de.jeanlucmakiola.agendula.data.tasks.recoveringFromProviderFailure
+import de.jeanlucmakiola.agendula.domain.TaskList
+import de.jeanlucmakiola.agendula.domain.export.ExportDocument
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.stateIn
+import kotlinx.coroutines.flow.update
+import kotlinx.coroutines.launch
+import javax.inject.Inject
+import kotlin.coroutines.cancellation.CancellationException
+
+/** How the last export ended, kept on screen rather than flashed past. */
+sealed interface ExportOutcome {
+    data class Success(val fileCount: Int) : ExportOutcome
+    data class Failure(val reason: ExportFailure) : ExportOutcome
+}
+
+data class ExportUiState(
+    val lists: List<TaskList> = emptyList(),
+    /** Lists the user has ticked *off*; everything else is included. */
+    val excluded: Set<Long> = emptySet(),
+    val running: Boolean = false,
+    val outcome: ExportOutcome? = null,
+) {
+    fun isSelected(listId: Long): Boolean = listId !in excluded
+
+    val selectedCount: Int get() = lists.count { isSelected(it.id) }
+}
+
+/**
+ * Drives the export screen. Holds the selection as an exclusion set so a list
+ * that appears while the screen is open is exported too — the natural reading of
+ * "everything, minus what I unticked".
+ */
+@HiltViewModel
+class ExportViewModel @Inject constructor(
+    repository: TasksRepository,
+    resolver: ProviderResolver,
+    private val exporter: TaskExporter,
+    private val writer: ExportWriter,
+) : ViewModel() {
+
+    private val excluded = MutableStateFlow(emptySet<Long>())
+    private val running = MutableStateFlow(false)
+    private val outcome = MutableStateFlow<ExportOutcome?>(null)
+
+    private var exportJob: Job? = null
+
+    // List ids are per-store, and Settings can switch stores with this ViewModel
+    // still alive — so the selection, the receipt and a write already addressing
+    // the old store's lists all go with it.
+    private val modeHandle = resolver.onModeChanged {
+        exportJob?.cancel()
+        excluded.value = emptySet()
+        outcome.value = null
+    }
+
+    override fun onCleared() {
+        modeHandle.close()
+    }
+
+    val state: StateFlow<ExportUiState> =
+        combine(
+            repository.taskLists().recoveringFromProviderFailure { emptyList() },
+            excluded,
+            running,
+            outcome,
+        ) { lists, excluded, running, outcome ->
+            ExportUiState(lists, excluded, running, outcome)
+        }.stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), ExportUiState())
+
+    fun toggle(listId: Long) = excluded.update { current ->
+        if (listId in current) current - listId else current + listId
+    }
+
+    /** Writes one `.ics` per list into a folder the user picked through SAF. */
+    fun exportToFolder(tree: Uri) = export { documents -> writer.writeToTree(tree, documents) }
+
+    /** Writes every list into a single zip the user named through SAF. */
+    fun exportToZip(target: Uri) = export { documents -> writer.writeZip(target, documents) }
+
+    private fun export(write: suspend (List<ExportDocument>) -> ExportResult) {
+        if (running.value) return
+        running.value = true
+        outcome.value = null
+        exportJob = viewModelScope.launch {
+            // Null means "every list" to the exporter, and is what an untouched
+            // screen should send: the flow may not have emitted a list yet.
+            val selection = excluded.value.takeIf { it.isNotEmpty() }
+                ?.let { skipped -> state.value.lists.map { it.id }.toSet() - skipped }
+            try {
+                val result = write(exporter.export(selection))
+                outcome.value = ExportOutcome.Success(result.fileCount)
+            } catch (cancelled: CancellationException) {
+                // Leaving the screen mid-write is not a failed export.
+                throw cancelled
+            } catch (error: Exception) {
+                outcome.value = ExportOutcome.Failure(
+                    (error as? ExportFailedException)?.failure ?: ExportFailure.WRITE_FAILED,
+                )
+            } finally {
+                running.value = false
+            }
+        }
+    }
+}

app/src/main/java/de/jeanlucmakiola/agendula/ui/lists/ListEditorSheet.kt

@@ -0,0 +1,295 @@
+package de.jeanlucmakiola.agendula.ui.lists
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.aspectRatio
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.heightIn
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.selection.selectable
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.rounded.Check
+import androidx.compose.material.icons.rounded.DeleteOutline
+import androidx.compose.material3.AlertDialog
+import androidx.compose.material3.Button
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableIntStateOf
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.saveable.rememberSaveable
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.focus.FocusRequester
+import androidx.compose.ui.focus.focusRequester
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.luminance
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.semantics.Role
+import androidx.compose.ui.semantics.contentDescription
+import androidx.compose.ui.semantics.semantics
+import androidx.compose.ui.text.input.ImeAction
+import androidx.compose.ui.unit.dp
+import de.jeanlucmakiola.agendula.R
+import de.jeanlucmakiola.agendula.domain.TaskList
+import de.jeanlucmakiola.agendula.ui.common.DefaultListColor
+import de.jeanlucmakiola.agendula.ui.common.ListColorChip
+import de.jeanlucmakiola.agendula.ui.common.ListPalette
+import de.jeanlucmakiola.floret.components.FullScreenPicker
+import de.jeanlucmakiola.floret.components.GroupedSurface
+import de.jeanlucmakiola.floret.components.InlineTextField
+import de.jeanlucmakiola.floret.components.Position
+import de.jeanlucmakiola.floret.components.pastelize
+
+private const val SWATCHES_PER_ROW = 6
+
+/**
+ * Create or edit a task list: a name field over the palette of list colours, on
+ * the family's full-screen sheet with the commit in its title bar.
+ *
+ * [initial] null is the create case. [onDelete] is null for a list the app must
+ * not remove — an account's collection belongs to its server — which is also why
+ * the destructive row only appears when it is non-null.
+ */
+@Composable
+fun ListEditorSheet(
+    initial: TaskList?,
+    onSave: (name: String, color: Int) -> Unit,
+    onDismiss: () -> Unit,
+    onDelete: (() -> Unit)? = null,
+) {
+    var name by rememberSaveable(initial?.id) { mutableStateOf(initial?.name.orEmpty()) }
+    var color by rememberSaveable(initial?.id) { mutableIntStateOf(initial?.color ?: DefaultListColor) }
+    var confirmDelete by rememberSaveable { mutableStateOf(false) }
+
+    val valid = name.isNotBlank()
+    val commit = {
+        if (valid) {
+            onSave(name.trim(), color)
+            onDismiss()
+        }
+    }
+
+    FullScreenPicker(
+        title = stringResource(if (initial == null) R.string.list_new_title else R.string.list_edit_title),
+        onDismiss = onDismiss,
+        actions = {
+            Button(
+                onClick = commit,
+                enabled = valid,
+                modifier = Modifier.padding(end = 12.dp),
+            ) { Text(stringResource(R.string.save)) }
+        },
+    ) {
+        NameField(
+            name = name,
+            color = color,
+            // A new list opens with the keyboard up: naming it is the whole task.
+            autoFocus = initial == null,
+            onNameChange = { name = it },
+            onImeAction = commit,
+        )
+
+        Spacer(Modifier.height(20.dp))
+        SectionLabel(stringResource(R.string.list_color))
+        ColorGrid(selected = color, onSelect = { color = it })
+
+        if (onDelete != null) {
+            Spacer(Modifier.height(24.dp))
+            DeleteRow(onClick = { confirmDelete = true })
+        }
+        Spacer(Modifier.height(24.dp))
+    }
+
+    if (confirmDelete && onDelete != null) {
+        DeleteListDialog(
+            listName = initial?.name.orEmpty(),
+            onConfirm = {
+                confirmDelete = false
+                onDelete()
+                onDismiss()
+            },
+            onDismiss = { confirmDelete = false },
+        )
+    }
+}
+
+/** The name, with the chosen colour beside it so the two read as one thing. */
+@Composable
+private fun NameField(
+    name: String,
+    color: Int,
+    autoFocus: Boolean,
+    onNameChange: (String) -> Unit,
+    onImeAction: () -> Unit,
+) {
+    val focusRequester = remember { FocusRequester() }
+    LaunchedEffect(autoFocus) { if (autoFocus) focusRequester.requestFocus() }
+    GroupedSurface(position = Position.Alone, modifier = Modifier.padding(horizontal = 16.dp)) {
+        Row(
+            modifier = Modifier.fillMaxWidth().heightIn(min = 72.dp).padding(horizontal = 16.dp),
+            verticalAlignment = Alignment.CenterVertically,
+            horizontalArrangement = Arrangement.spacedBy(16.dp),
+        ) {
+            ListColorChip(color)
+            InlineTextField(
+                value = name,
+                onValueChange = onNameChange,
+                placeholder = stringResource(R.string.list_name_hint),
+                imeAction = ImeAction.Done,
+                onImeAction = onImeAction,
+                modifier = Modifier.fillMaxWidth().focusRequester(focusRequester),
+            )
+        }
+    }
+}
+
+/** The palette as two rows of round swatches; the chosen one carries a check. */
+@Composable
+private fun ColorGrid(selected: Int, onSelect: (Int) -> Unit) {
+    val dark = isSystemInDarkTheme()
+    GroupedSurface(position = Position.Alone, modifier = Modifier.padding(horizontal = 16.dp)) {
+        Column(
+            modifier = Modifier.padding(horizontal = 12.dp, vertical = 16.dp),
+            verticalArrangement = Arrangement.spacedBy(12.dp),
+        ) {
+            ListPalette.chunked(SWATCHES_PER_ROW).forEach { row ->
+                Row(
+                    modifier = Modifier.fillMaxWidth(),
+                    horizontalArrangement = Arrangement.spacedBy(8.dp),
+                ) {
+                    row.forEach { swatch ->
+                        Swatch(
+                            color = swatch,
+                            dark = dark,
+                            selected = swatch == selected,
+                            onClick = { onSelect(swatch) },
+                            modifier = Modifier.weight(1f),
+                        )
+                    }
+                    // Keeps a short final row's swatches at the same size as a full
+                    // one's rather than stretching them across the width.
+                    repeat(SWATCHES_PER_ROW - row.size) { Spacer(Modifier.weight(1f)) }
+                }
+            }
+        }
+    }
+}
+
+@Composable
+private fun Swatch(
+    color: Int,
+    dark: Boolean,
+    selected: Boolean,
+    onClick: () -> Unit,
+    modifier: Modifier = Modifier,
+) {
+    val fill = pastelize(color, dark)
+    val label = stringResource(colorLabel(color))
+    Box(
+        modifier = modifier
+            .aspectRatio(1f)
+            .clip(CircleShape)
+            .background(fill)
+            // selectable, not clickable: the swatch carries its chosen state in
+            // semantics, so the check below is decoration rather than the only cue.
+            .selectable(selected = selected, role = Role.RadioButton, onClick = onClick)
+            .semantics { contentDescription = label },
+        contentAlignment = Alignment.Center,
+    ) {
+        if (selected) {
+            Icon(
+                Icons.Rounded.Check,
+                contentDescription = null,
+                tint = if (fill.luminance() > 0.5f) Color.Black else Color.White,
+                modifier = Modifier.size(22.dp),
+            )
+        }
+    }
+}
+
+@Composable
+private fun DeleteRow(onClick: () -> Unit) {
+    GroupedSurface(
+        position = Position.Alone,
+        modifier = Modifier.padding(horizontal = 16.dp),
+        onClick = onClick,
+        color = MaterialTheme.colorScheme.errorContainer,
+    ) {
+        Row(
+            modifier = Modifier.fillMaxWidth().heightIn(min = 64.dp).padding(horizontal = 20.dp),
+            verticalAlignment = Alignment.CenterVertically,
+            horizontalArrangement = Arrangement.spacedBy(16.dp),
+        ) {
+            Icon(
+                Icons.Rounded.DeleteOutline,
+                contentDescription = null,
+                tint = MaterialTheme.colorScheme.onErrorContainer,
+            )
+            Text(
+                text = stringResource(R.string.list_delete),
+                style = MaterialTheme.typography.bodyLarge,
+                color = MaterialTheme.colorScheme.onErrorContainer,
+            )
+        }
+    }
+}
+
+@Composable
+private fun DeleteListDialog(listName: String, onConfirm: () -> Unit, onDismiss: () -> Unit) {
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text(stringResource(R.string.list_delete_confirm_title)) },
+        text = { Text(stringResource(R.string.list_delete_confirm_message, listName)) },
+        confirmButton = {
+            TextButton(onClick = onConfirm) {
+                Text(stringResource(R.string.delete), color = MaterialTheme.colorScheme.error)
+            }
+        },
+        dismissButton = {
+            TextButton(onClick = onDismiss) { Text(stringResource(R.string.dialog_cancel)) }
+        },
+    )
+}
+
+@Composable
+private fun SectionLabel(text: String) {
+    Text(
+        text = text,
+        style = MaterialTheme.typography.labelMedium,
+        color = MaterialTheme.colorScheme.onSurfaceVariant,
+        modifier = Modifier.padding(start = 28.dp, end = 28.dp, bottom = 8.dp),
+    )
+}
+
+/** Names the palette entries for screen readers; anything else is just "colour". */
+private fun colorLabel(color: Int): Int = when (ListPalette.indexOf(color)) {
+    0 -> R.string.list_color_mauve
+    1 -> R.string.list_color_red
+    2 -> R.string.list_color_orange
+    3 -> R.string.list_color_amber
+    4 -> R.string.list_color_olive
+    5 -> R.string.list_color_green
+    6 -> R.string.list_color_teal
+    7 -> R.string.list_color_cyan
+    8 -> R.string.list_color_blue
+    9 -> R.string.list_color_indigo
+    10 -> R.string.list_color_purple
+    11 -> R.string.list_color_pink
+    else -> R.string.list_color
+}

app/src/main/java/de/jeanlucmakiola/agendula/ui/lists/ListsScreen.kt

@@ -46,6 +46,7 @@ import androidx.compose.material.icons.rounded.Upcoming
 import androidx.compose.material3.CircularWavyProgressIndicator
 import androidx.compose.material3.ExperimentalMaterial3ExpressiveApi
 import androidx.compose.material3.ExtendedFloatingActionButton
+import androidx.compose.material3.FilledTonalButton
 import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
@@ -80,6 +81,10 @@ import de.jeanlucmakiola.agendula.domain.Task
 import de.jeanlucmakiola.agendula.domain.TaskFilter
 import de.jeanlucmakiola.agendula.ui.common.ActionShapes
 import de.jeanlucmakiola.floret.components.GroupedRow
+import de.jeanlucmakiola.floret.components.SnackChip
+import de.jeanlucmakiola.floret.components.SnackChipHeight
+import de.jeanlucmakiola.floret.components.SnackChipMargin
+import kotlinx.coroutines.delay
 import de.jeanlucmakiola.agendula.ui.common.ListColorChip
 import de.jeanlucmakiola.agendula.ui.common.ShapedActionButton
 import de.jeanlucmakiola.agendula.ui.common.priorityAccent
@@ -108,10 +113,22 @@ fun ListsScreen(
     val state by viewModel.state.collectAsStateWithLifecycle()
     var query by rememberSaveable { mutableStateOf("") }
     var searchActive by rememberSaveable { mutableStateOf(false) }
+    var newList by rememberSaveable { mutableStateOf(false) }
     val closeSearch = {
         query = ""
         searchActive = false
     }
+    // With no lists there is nowhere to put a task, so the primary action becomes
+    // making one — otherwise a fresh install's FAB opens a form that cannot save.
+    val noLists = (state as? ListsUiState.Content)?.groups?.isEmpty() == true
+    // The sheet closes on save, so a refused write has to report itself here.
+    val writeFailure by viewModel.writeFailure.collectAsStateWithLifecycle()
+    LaunchedEffect(writeFailure) {
+        if (writeFailure != null) {
+            delay(4_000)
+            viewModel.clearWriteFailure()
+        }
+    }
     // System back closes search before leaving the screen.
     BackHandler(enabled = searchActive, onBack = closeSearch)
 
@@ -130,9 +147,11 @@ fun ListsScreen(
             // The FAB would otherwise float over the search results.
             if (!searchActive) {
                 ExtendedFloatingActionButton(
-                    onClick = onNewTask,
+                    onClick = if (noLists) ({ newList = true }) else onNewTask,
                     icon = { Icon(Icons.Rounded.Add, contentDescription = null) },
-                    text = { Text(stringResource(R.string.new_task)) },
+                    text = {
+                        Text(stringResource(if (noLists) R.string.list_add else R.string.new_task))
+                    },
                 )
             }
         },
@@ -147,6 +166,7 @@ fun ListsScreen(
                         state = s,
                         onOpenFilter = onOpenFilter,
                         onOpenTask = onOpenTask,
+                        onNewList = { newList = true },
                         topPadding = 0.dp,
                         bottomPadding = inner.calculateBottomPadding() + 96.dp,
                     )
@@ -166,8 +186,33 @@ fun ListsScreen(
                     }
                 }
             }
+            // Anchored beside the FAB, at its height — the same receipt placement
+            // the task list uses.
+            Box(
+                modifier = Modifier
+                    .align(Alignment.BottomStart)
+                    .padding(
+                        start = SnackChipMargin,
+                        bottom = inner.calculateBottomPadding() + SnackChipMargin,
+                    )
+                    .height(SnackChipHeight),
+                contentAlignment = Alignment.CenterStart,
+            ) {
+                SnackChip(
+                    visible = writeFailure != null,
+                    message = stringResource(R.string.list_save_failed),
+                )
+            }
         }
     }
+
+    if (newList) {
+        ListEditorSheet(
+            initial = null,
+            onSave = viewModel::createList,
+            onDismiss = { newList = false },
+        )
+    }
 }
 
 @Composable
@@ -175,6 +220,7 @@ private fun ListsContent(
     state: ListsUiState.Content,
     onOpenFilter: (TaskFilter) -> Unit,
     onOpenTask: (Long) -> Unit,
+    onNewList: () -> Unit,
     topPadding: androidx.compose.ui.unit.Dp,
     bottomPadding: androidx.compose.ui.unit.Dp,
 ) {
@@ -215,9 +261,21 @@ private fun ListsContent(
         }
 
         if (state.groups.isEmpty()) {
-            item { CenteredMessage(stringResource(R.string.lists_empty), PaddingValues(top = 24.dp)) }
+            item { EmptyLists(onNewList = onNewList) }
         } else {
-            item { SectionHeader(stringResource(R.string.lists_header)) }
+            item {
+                SectionHeader(
+                    text = stringResource(R.string.lists_header),
+                    action = {
+                        ShapedActionButton(
+                            shape = ActionShapes.AddList,
+                            icon = Icons.Rounded.Add,
+                            contentDescription = stringResource(R.string.list_add),
+                            onClick = onNewList,
+                        )
+                    },
+                )
+            }
             state.groups.forEach { group ->
                 item(key = "acct-${group.accountName}") { AccountHeader(group.accountName) }
                 itemsIndexed(group.lists, key = { _, o -> o.list.id }) { index, overview ->
@@ -243,6 +301,28 @@ private fun ListsContent(
     }
 }
 
+/** No lists at all — a fresh install, where nothing else on this screen works yet. */
+@Composable
+private fun EmptyLists(onNewList: () -> Unit) {
+    Column(
+        modifier = Modifier.fillMaxWidth().padding(horizontal = 32.dp, vertical = 32.dp),
+        horizontalAlignment = Alignment.CenterHorizontally,
+        verticalArrangement = Arrangement.spacedBy(16.dp),
+    ) {
+        Text(
+            text = stringResource(R.string.lists_empty),
+            style = MaterialTheme.typography.bodyLarge,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+            textAlign = TextAlign.Center,
+        )
+        FilledTonalButton(onClick = onNewList) {
+            Icon(Icons.Rounded.Add, contentDescription = null, modifier = Modifier.size(18.dp))
+            Spacer(Modifier.width(8.dp))
+            Text(stringResource(R.string.lists_empty_action))
+        }
+    }
+}
+
 /**
  * The home top bar. There is no title — the launcher icon already says which app
  * this is. Settings is pinned at the right; the search action sits just left of it
@@ -419,7 +499,7 @@ private fun SearchResults(
             }
         } else {
             LazyColumn(modifier = Modifier.fillMaxSize()) {
-                items(results, key = { it.id }) { task ->
+                items(results, key = { it.occurrenceKey }) { task ->
                     UpcomingRow(task = task, onClick = { onOpenTask(task.taskId) })
                 }
             }
@@ -655,12 +735,25 @@ private fun SmartCard(count: SmartCount, modifier: Modifier = Modifier, onClick:
 }
 
 @Composable
-private fun SectionHeader(text: String) {
-    Text(
-        text = text,
-        style = MaterialTheme.typography.titleMedium,
-        modifier = Modifier.padding(start = 28.dp, end = 28.dp, top = 16.dp, bottom = 4.dp),
-    )
+private fun SectionHeader(text: String, action: (@Composable () -> Unit)? = null) {
+    Row(
+        modifier = Modifier
+            .fillMaxWidth()
+            .padding(
+                start = 28.dp,
+                end = if (action == null) 28.dp else 20.dp,
+                top = if (action == null) 16.dp else 12.dp,
+                bottom = 4.dp,
+            ),
+        verticalAlignment = Alignment.CenterVertically,
+    ) {
+        Text(
+            text = text,
+            style = MaterialTheme.typography.titleMedium,
+            modifier = Modifier.weight(1f),
+        )
+        action?.invoke()
+    }
 }
 
 @Composable

app/src/main/java/de/jeanlucmakiola/agendula/ui/lists/ListsViewModel.kt

@@ -4,21 +4,30 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
 import de.jeanlucmakiola.agendula.data.tasks.TasksRepository
+import de.jeanlucmakiola.agendula.data.tasks.recoveringFromProviderFailure
 import de.jeanlucmakiola.floret.time.DayWindow
 import de.jeanlucmakiola.agendula.domain.SmartList
 import de.jeanlucmakiola.agendula.domain.Task
 import de.jeanlucmakiola.agendula.domain.TaskFilter
 import de.jeanlucmakiola.agendula.domain.TaskFiltering
 import de.jeanlucmakiola.agendula.domain.TaskList
+import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
-import kotlinx.coroutines.flow.catch
+import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.stateIn
+import kotlinx.coroutines.launch
 import java.time.ZoneId
 import javax.inject.Inject
 import kotlin.time.Clock
 
+/**
+ * What a list write failed at. The screens turn this into wording; the view
+ * models stay free of resources.
+ */
+enum class ListWriteFailure { SAVE, DELETE }
+
 data class ListOverview(val list: TaskList, val openCount: Int)
 data class AccountGroup(val accountName: String, val lists: List<ListOverview>)
 data class SmartCount(val smart: SmartList, val count: Int)
@@ -44,7 +53,7 @@ private const val UPCOMING_PREVIEW = 3
 /** The home overview: smart lists with live counts, then user lists by account. */
 @HiltViewModel
 class ListsViewModel @Inject constructor(
-    repository: TasksRepository,
+    private val repository: TasksRepository,
 ) : ViewModel() {
 
     val state: StateFlow<ListsUiState> =
@@ -56,7 +65,7 @@ class ListsViewModel @Inject constructor(
             repository.tasks(TaskFilter.Smart(SmartList.COMPLETED)),
         ) { lists, openTasks, completedTasks ->
             buildContent(lists, openTasks, completedTasks) as ListsUiState
-        }.catch { emit(ListsUiState.Failure) }
+        }.recoveringFromProviderFailure { ListsUiState.Failure }
             .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), ListsUiState.Loading)
 
     private fun buildContent(
@@ -112,4 +121,22 @@ class ListsViewModel @Inject constructor(
             allTasks = openTasks + completedTasks,
         )
     }
+
+    private val _writeFailure = MutableStateFlow<ListWriteFailure?>(null)
+
+    /** Set when a list write is refused; the screen shows it and clears it. */
+    val writeFailure: StateFlow<ListWriteFailure?> = _writeFailure.asStateFlow()
+
+    fun clearWriteFailure() { _writeFailure.value = null }
+
+    /**
+     * Create a device-only list. The lists flow picks it up on the store change;
+     * a refusal (External mode, a provider that says no) surfaces through
+     * [writeFailure] rather than vanishing, because the sheet has already closed.
+     */
+    fun createList(name: String, color: Int) = viewModelScope.launch {
+        if (name.isBlank()) return@launch
+        runCatching { repository.createLocalList(name.trim(), color) }
+            .onFailure { _writeFailure.value = ListWriteFailure.SAVE }
+    }
 }

app/src/main/java/de/jeanlucmakiola/agendula/ui/permission/PermissionViewModel.kt

@@ -1,13 +1,25 @@
 package de.jeanlucmakiola.agendula.ui.permission
 
 import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
+import de.jeanlucmakiola.agendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.agendula.data.tasks.ProviderResolver
 import de.jeanlucmakiola.agendula.data.tasks.ProviderStatus
+import de.jeanlucmakiola.agendula.data.tasks.StorageMode
 import de.jeanlucmakiola.agendula.data.tasks.TasksRepository
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.channels.awaitClose
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.buffer
 import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
-import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.callbackFlow
+import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.stateIn
+import kotlinx.coroutines.flow.update
+import kotlinx.coroutines.launch
 import javax.inject.Inject
 
 data class PermissionUiState(
@@ -20,23 +32,51 @@ data class PermissionUiState(
  * Gates app entry: is a tasks provider installed, and do we hold its permissions?
  * The Composable owns the actual permission-launcher and store intents; this VM
  * supplies the [status] and the exact permission strings to ask for.
+ *
+ * In the default Own mode this gate never appears at all — the store is our own
+ * Room database, so there is nothing to install and nothing to grant. It exists
+ * for External mode, which also makes it the only screen an External user can
+ * reach once their provider app stops answering: hence [useOwnStore].
  */
 @HiltViewModel
 class PermissionViewModel @Inject constructor(
     private val repository: TasksRepository,
     private val providerResolver: ProviderResolver,
+    private val prefs: SettingsPrefs,
 ) : ViewModel() {
 
-    private val _state = MutableStateFlow(PermissionUiState())
-    val state: StateFlow<PermissionUiState> = _state.asStateFlow()
+    private val refreshes = MutableStateFlow(0)
 
-    init { refresh() }
+    // Re-evaluated when the *resolver's* mode lands, not when the preference is
+    // written: anything read in between still answers for the store we just left.
+    // Conflated, as everywhere else this signal is bridged: only the latest mode
+    // matters, and a full buffer drops it rather than the ones it supersedes.
+    private val modeChanges: Flow<Unit> = callbackFlow {
+        trySend(Unit)
+        val handle = providerResolver.onModeChanged { trySend(Unit) }
+        awaitClose { handle.close() }
+    }.buffer(Channel.CONFLATED)
+
+    val state: StateFlow<PermissionUiState> =
+        combine(refreshes, modeChanges) { _, _ -> currentState() }
+            .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), currentState())
 
     /** Re-read provider + permission state (call after returning from a request). */
-    fun refresh() {
+    fun refresh() = refreshes.update { it + 1 }
+
+    /**
+     * Leave a store this device can no longer read. The provider app can be
+     * uninstalled, or its permission revoked, after External was chosen — and the
+     * gate is then the only screen reachable, Settings included. Our own store
+     * always reads, so it is the way out.
+     */
+    fun useOwnStore() = viewModelScope.launch { prefs.setStorageMode(StorageMode.OWN) }
+
+    private fun currentState(): PermissionUiState {
         val provider = providerResolver.resolve()
-        _state.value = PermissionUiState(
+        return PermissionUiState(
             status = repository.providerStatus(),
+            // Null in OWN mode, where there is no provider and nothing to grant.
             permissionsToRequest = provider
                 ?.let { listOf(it.readPermission, it.writePermission) }
                 .orEmpty(),

app/src/main/java/de/jeanlucmakiola/agendula/ui/settings/SettingsScreen.kt

@@ -43,11 +43,13 @@ import androidx.compose.material.icons.filled.Gavel
 import androidx.compose.material.icons.filled.Language
 import androidx.compose.material.icons.filled.Notifications
 import androidx.compose.material.icons.filled.Palette
+import androidx.compose.material.icons.filled.Translate
 import androidx.compose.material.icons.filled.Tune
 import androidx.compose.material.icons.rounded.AccountTree
 import androidx.compose.material.icons.rounded.Circle
 import androidx.compose.material.icons.rounded.Flag
 import androidx.compose.material.icons.rounded.Percent
+import androidx.compose.material.icons.rounded.Storage
 import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
@@ -55,7 +57,6 @@ import androidx.compose.material3.Surface
 import androidx.compose.material3.Switch
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
-import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
@@ -74,17 +75,14 @@ import androidx.compose.ui.unit.dp
 import androidx.core.content.ContextCompat
 import androidx.core.net.toUri
 import androidx.hilt.navigation.compose.hiltViewModel
-import androidx.lifecycle.Lifecycle
-import androidx.lifecycle.LifecycleEventObserver
-import androidx.lifecycle.compose.LocalLifecycleOwner
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import de.jeanlucmakiola.agendula.R
 import de.jeanlucmakiola.agendula.data.prefs.ThemeMode
 import de.jeanlucmakiola.agendula.domain.TaskFormField
+import de.jeanlucmakiola.agendula.ui.export.ExportScreen
 import de.jeanlucmakiola.floret.components.AboutCard
 import de.jeanlucmakiola.floret.components.AboutLink
 import de.jeanlucmakiola.floret.components.CollapsingScaffold
-import de.jeanlucmakiola.floret.components.LanguagePickerRow
 import de.jeanlucmakiola.floret.components.GroupedRow
 import de.jeanlucmakiola.floret.components.OptionPicker
 import de.jeanlucmakiola.floret.components.Position
@@ -92,12 +90,26 @@ import de.jeanlucmakiola.agendula.ui.common.ReminderLeadPicker
 import de.jeanlucmakiola.floret.components.pastelize
 import de.jeanlucmakiola.floret.components.positionOf
 import de.jeanlucmakiola.floret.identity.collapseExit
+import de.jeanlucmakiola.floret.locale.AppLanguage
 import de.jeanlucmakiola.floret.identity.expandEnter
 import de.jeanlucmakiola.floret.reminders.ReminderOverride
+import de.jeanlucmakiola.floret.reminders.reminderOverrideFor
+import de.jeanlucmakiola.agendula.ui.common.OnResume
 import de.jeanlucmakiola.agendula.ui.common.reminderLeadTimeLabel
 
 /** The settings sub-screens reached from the hub's category rows. */
-private enum class SettingsSection { Appearance, TaskForm, Reminders }
+private enum class SettingsSection {
+    Appearance,
+    TaskForm,
+    Reminders,
+    Storage,
+    Export,
+    ;
+
+    /** Where back goes: Export is opened from Storage, not from the hub. */
+    val parent: SettingsSection?
+        get() = if (this == Export) Storage else null
+}
 
 /**
  * Token-based accent for a leading icon chip (container / on-container pair),
@@ -123,7 +135,7 @@ fun SettingsScreen(
 
     // Inside a sub-screen, system back (button or gesture) returns to the hub
     // rather than popping the whole Settings destination to the lists overview.
-    BackHandler(enabled = section != null) { section = null }
+    BackHandler(enabled = section != null) { section = section?.parent }
 
     Box(
         modifier = modifier
@@ -141,6 +153,19 @@ fun SettingsScreen(
         SlideInSection(visible = section == SettingsSection.Reminders) {
             RemindersScreen(state = state, viewModel = viewModel, onBack = { section = null })
         }
+        // Storage stays composed under Export, so the deeper screen slides over it.
+        val storageOpen = section == SettingsSection.Storage ||
+            section?.parent == SettingsSection.Storage
+        SlideInSection(visible = storageOpen) {
+            StorageScreen(
+                viewModel = viewModel,
+                onOpenExport = { section = SettingsSection.Export },
+                onBack = { section = null },
+            )
+        }
+        SlideInSection(visible = section == SettingsSection.Export) {
+            ExportScreen(onBack = { section = SettingsSection.Storage })
+        }
     }
 }
 
@@ -210,19 +235,77 @@ private fun SettingsHub(
             leading = { CategoryIcon(Icons.Default.Notifications, ChipAccent.Primary) },
             onClick = { onOpenSection(SettingsSection.Reminders) },
         )
-        LanguagePickerRow(
+        GroupedRow(
+            title = stringResource(R.string.settings_section_storage),
+            summary = stringResource(R.string.settings_storage_subtitle),
             position = Position.Middle,
-            title = stringResource(R.string.settings_language),
-            autoLabel = stringResource(R.string.settings_language_auto),
-            localesConfig = R.xml.locales_config,
-            leading = { CategoryIcon(Icons.Default.Language, ChipAccent.Neutral) },
+            leading = { CategoryIcon(Icons.Rounded.Storage, ChipAccent.Neutral) },
+            onClick = { onOpenSection(SettingsSection.Storage) },
         )
+        LanguageRow(position = Position.Middle)
         ReportProblemRow(position = Position.Bottom)
 
         AppVersionText()
     }
 }
 
+/**
+ * The app-language row. Deliberately not floret-kit's `LanguagePickerRow`: the
+ * picker it opens carries a "Help translate" header, and inviting contributions
+ * right where a user goes looking for their language is app-specific framing,
+ * not a family primitive. Everything else matches that recipe.
+ */
+@Composable
+private fun LanguageRow(position: Position) {
+    val context = LocalContext.current
+    // Setting a locale recreates the activity; mirror the choice locally so the
+    // row updates instantly even before the recreation lands.
+    var current by remember { mutableStateOf(AppLanguage.currentTag()) }
+    var showDialog by remember { mutableStateOf(false) }
+
+    // null = follow the system; the rest are BCP-47 tags from locales_config.xml.
+    val options = remember { listOf<String?>(null) + AppLanguage.supportedTags(context, R.xml.locales_config) }
+
+    GroupedRow(
+        title = stringResource(R.string.settings_language),
+        summary = languageLabel(current),
+        position = position,
+        leading = { CategoryIcon(Icons.Default.Language, ChipAccent.Neutral) },
+        onClick = { showDialog = true },
+    )
+
+    if (showDialog) {
+        OptionPicker(
+            title = stringResource(R.string.settings_language),
+            predictiveBack = true,
+            options = options,
+            selected = current,
+            label = { languageLabel(it) },
+            onSelect = {
+                current = it
+                AppLanguage.apply(it)
+            },
+            onDismiss = { showDialog = false },
+            // Invite contributions right where users pick their language.
+            header = {
+                val translateUrl = stringResource(R.string.about_translate_url)
+                GroupedRow(
+                    title = stringResource(R.string.settings_translate),
+                    summary = stringResource(R.string.settings_translate_hint),
+                    position = Position.Alone,
+                    leading = { CategoryIcon(Icons.Default.Translate, ChipAccent.Neutral) },
+                    onClick = { openUrl(context, translateUrl) },
+                )
+                Spacer(Modifier.height(16.dp))
+            },
+        )
+    }
+}
+
+@Composable
+private fun languageLabel(tag: String?): String =
+    if (tag == null) stringResource(R.string.settings_language_auto) else AppLanguage.displayName(tag)
+
 /** Opens the project's issue tracker; no data leaves the device until submitted. */
 @Composable
 private fun ReportProblemRow(position: Position) {
@@ -483,10 +566,10 @@ private fun RemindersScreen(
     if (showOffset) {
         ReminderLeadPicker(
             title = stringResource(R.string.settings_default_reminder),
-            selected = ReminderOverride.Minutes(state.settings.reminderLeadMinutes),
+            selected = ReminderOverride.Minutes(listOf(state.settings.reminderLeadMinutes)),
             allowInherit = false,
             allowNone = false,
-            onSelect = { if (it is ReminderOverride.Minutes) viewModel.setReminderLeadMinutes(it.minutes) },
+            onSelect = { if (it is ReminderOverride.Minutes) viewModel.setReminderLeadMinutes(it.minutes.first()) },
             onDismiss = { showOffset = false },
         )
     }
@@ -504,14 +587,8 @@ private fun RemindersScreen(
 }
 
 /** The stored override for [listId], as a picker choice (absent → inherit). */
-private fun listOverrideChoice(state: SettingsUiState, listId: Long): ReminderOverride {
-    val map = state.settings.perListReminderOverride
-    return when {
-        !map.containsKey(listId) -> ReminderOverride.Inherit
-        map[listId] == null -> ReminderOverride.None
-        else -> ReminderOverride.Minutes(map.getValue(listId)!!)
-    }
-}
+private fun listOverrideChoice(state: SettingsUiState, listId: Long): ReminderOverride =
+    state.settings.perListReminderOverride.reminderOverrideFor(listId)
 
 /** Row summary for a list: its override, or the inherited global default. */
 @Composable
@@ -519,7 +596,7 @@ private fun listOverrideSummary(choice: ReminderOverride, globalDefault: Int): S
     ReminderOverride.Inherit ->
         stringResource(R.string.settings_list_reminder_inherits, reminderLeadTimeLabel(globalDefault))
     ReminderOverride.None -> stringResource(R.string.reminder_none)
-    is ReminderOverride.Minutes -> reminderLeadTimeLabel(choice.minutes)
+    is ReminderOverride.Minutes -> reminderLeadTimeLabel(choice.minutes.first())
 }
 
 // ---------------------------------------------------------------------------
@@ -623,15 +700,10 @@ private fun rememberExactAlarmAllowed(context: Context): Boolean {
                 context.getSystemService(AlarmManager::class.java).canScheduleExactAlarms(),
         )
     }
-    val lifecycle = LocalLifecycleOwner.current.lifecycle
-    DisposableEffect(lifecycle) {
-        val obs = LifecycleEventObserver { _, event ->
-            if (event == Lifecycle.Event.ON_RESUME && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
-                allowed = context.getSystemService(AlarmManager::class.java).canScheduleExactAlarms()
-            }
+    OnResume {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
+            allowed = context.getSystemService(AlarmManager::class.java).canScheduleExactAlarms()
         }
-        lifecycle.addObserver(obs)
-        onDispose { lifecycle.removeObserver(obs) }
     }
     return allowed
 }

app/src/main/java/de/jeanlucmakiola/agendula/ui/settings/SettingsViewModel.kt

@@ -3,18 +3,27 @@ package de.jeanlucmakiola.agendula.ui.settings
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
+import de.jeanlucmakiola.agendula.data.di.IoDispatcher
 import de.jeanlucmakiola.agendula.data.prefs.Settings
 import de.jeanlucmakiola.agendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.agendula.data.prefs.ThemeMode
+import de.jeanlucmakiola.agendula.data.tasks.ProviderEnvironment
+import de.jeanlucmakiola.agendula.data.tasks.ProviderResolver
+import de.jeanlucmakiola.agendula.data.tasks.StorageMode
+import de.jeanlucmakiola.agendula.data.tasks.TaskProvider
 import de.jeanlucmakiola.agendula.data.tasks.TasksRepository
+import de.jeanlucmakiola.agendula.data.tasks.recoveringFromProviderFailure
 import de.jeanlucmakiola.agendula.domain.TaskFormField
 import de.jeanlucmakiola.agendula.domain.TaskList
 import de.jeanlucmakiola.floret.reminders.ReminderOverride
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
-import kotlinx.coroutines.flow.catch
 import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.stateIn
+import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 
@@ -23,6 +32,22 @@ data class SettingsUiState(
     val lists: List<TaskList> = emptyList(),
 )
 
+/**
+ * The storage half of Settings: which store is active, and what picking the
+ * other one would mean on this device.
+ *
+ * Kept apart from [SettingsUiState] because that one is collected for the whole
+ * Activity lifetime to drive the theme, and re-probing PackageManager on every
+ * theme emission would be work for nothing.
+ */
+data class StorageUiState(
+    val mode: StorageMode,
+    /** The external provider installed here, or null when there is none to pick. */
+    val external: TaskProvider? = null,
+    /** That provider's own app name, for a row that names what it is switching to. */
+    val externalLabel: String? = null,
+)
+
 /**
  * Drives both the Settings screen and the app theme (MainActivity collects the
  * same instance), so a theme change applies app-wide at once.
@@ -30,14 +55,48 @@ data class SettingsUiState(
 @HiltViewModel
 class SettingsViewModel @Inject constructor(
     private val prefs: SettingsPrefs,
+    private val resolver: ProviderResolver,
+    private val environment: ProviderEnvironment,
+    @IoDispatcher io: CoroutineDispatcher,
     repository: TasksRepository,
 ) : ViewModel() {
 
+    // MainActivity collects this for the theme, above the permission gate and for
+    // the whole Activity lifetime — so the list flow must survive the pre-grant
+    // SecurityException and recover once permission is given, not die for good.
     val state: StateFlow<SettingsUiState> =
-        combine(prefs.settings, repository.taskLists().catch { emit(emptyList()) }) { settings, lists ->
+        combine(
+            prefs.settings,
+            repository.taskLists().recoveringFromProviderFailure { emptyList() },
+        ) { settings, lists ->
             SettingsUiState(settings, lists)
         }.stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), SettingsUiState())
 
+    // Bumped to re-probe the device; installing a provider or granting its
+    // permission happens outside the app, so nothing else would emit.
+    private val providerProbe = MutableStateFlow(0)
+
+    // Null until the first emission lands: the mode comes from DataStore and the
+    // rest from PackageManager, off the main thread, so any seeded default would
+    // name the wrong store for the first frames. flowOn, because every field here
+    // costs a PackageManager lookup or a permission check.
+    val storage: StateFlow<StorageUiState?> =
+        combine(prefs.storageMode, providerProbe) { stored, _ ->
+            val external = resolver.resolveExternal()
+            StorageUiState(
+                // No stored choice is the normal state; show what autoMode resolves
+                // to rather than a default that may not be the store in use.
+                mode = stored ?: resolver.autoMode(),
+                external = external,
+                externalLabel = external?.packageName?.let(environment::appLabel),
+            )
+        }.flowOn(io).stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), null)
+
+    /** Re-read the device's provider state, after a permission request or a resume. */
+    fun refreshStorage() = providerProbe.update { it + 1 }
+
+    fun setStorageMode(mode: StorageMode) = viewModelScope.launch { prefs.setStorageMode(mode) }
+
     fun setThemeMode(mode: ThemeMode) = viewModelScope.launch { prefs.setThemeMode(mode) }
     fun setDynamicColor(enabled: Boolean) = viewModelScope.launch { prefs.setDynamicColor(enabled) }
     fun setDefaultList(id: Long?) = viewModelScope.launch { prefs.setDefaultListId(id) }

app/src/main/java/de/jeanlucmakiola/agendula/ui/settings/StorageScreen.kt

@@ -0,0 +1,203 @@
+package de.jeanlucmakiola.agendula.ui.settings
+
+import android.content.Context
+import android.content.Intent
+import android.provider.Settings
+import androidx.activity.compose.rememberLauncherForActivityResult
+import androidx.activity.result.contract.ActivityResultContracts
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.rounded.Apps
+import androidx.compose.material.icons.rounded.PhoneAndroid
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.unit.dp
+import androidx.core.net.toUri
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import de.jeanlucmakiola.agendula.R
+import de.jeanlucmakiola.agendula.data.tasks.StorageMode
+import de.jeanlucmakiola.agendula.data.tasks.TaskProvider
+import de.jeanlucmakiola.agendula.ui.common.OnResume
+import de.jeanlucmakiola.floret.components.CollapsingScaffold
+import de.jeanlucmakiola.floret.components.FullScreenPicker
+import de.jeanlucmakiola.floret.components.GroupedRow
+import de.jeanlucmakiola.floret.components.Position
+import de.jeanlucmakiola.floret.components.SelectedCheck
+
+/**
+ * Where the tasks live: the store picker the resolver's `autoMode()` has always
+ * assumed, plus the way out of a store that lives in our own private storage.
+ */
+@Composable
+internal fun StorageScreen(
+    viewModel: SettingsViewModel,
+    onOpenExport: () -> Unit,
+    onBack: () -> Unit,
+) {
+    val context = LocalContext.current
+    val storage by viewModel.storage.collectAsStateWithLifecycle()
+    var showPicker by remember { mutableStateOf(false) }
+    var denied by remember { mutableStateOf(false) }
+
+    // The mode is committed only once the grant is in — switching first drops the
+    // user on the app-wide permission gate.
+    val permissionLauncher = rememberLauncherForActivityResult(
+        contract = ActivityResultContracts.RequestMultiplePermissions(),
+    ) { grants ->
+        viewModel.refreshStorage()
+        val granted = grants.isNotEmpty() && grants.values.all { it }
+        denied = !granted
+        if (granted) viewModel.setStorageMode(StorageMode.EXTERNAL)
+    }
+
+    // A provider can be installed, or its permission revoked, while we're away.
+    // Deliberately does not clear [denied]: this fires on returning from the
+    // permission dialog too, and would wipe the refusal before it is read.
+    OnResume { viewModel.refreshStorage() }
+
+    CollapsingScaffold(title = stringResource(R.string.settings_section_storage), onBack = onBack) {
+        GroupedRow(
+            title = stringResource(R.string.settings_task_store),
+            summary = storage?.let { storeLabel(it) },
+            position = Position.Top,
+            // Nothing to pick until the stored mode has landed; opening the picker
+            // on the seeded state would offer the wrong store as the current one.
+            onClick = storage?.let {
+                {
+                    denied = false
+                    showPicker = true
+                }
+            },
+        )
+        GroupedRow(
+            title = stringResource(R.string.settings_export),
+            summary = stringResource(R.string.settings_export_hint),
+            position = Position.Bottom,
+            onClick = onOpenExport,
+        )
+
+        if (denied) {
+            Spacer(Modifier.height(16.dp))
+            GroupedRow(
+                title = stringResource(R.string.settings_store_permission_denied),
+                summary = stringResource(R.string.settings_store_permission_denied_hint),
+                position = Position.Alone,
+                onClick = { context.openAppSettings() },
+            )
+        }
+    }
+
+    storage?.let { state ->
+        if (showPicker) {
+            StorePicker(
+                storage = state,
+                onSelect = { mode ->
+                    val external = state.external
+                    if (mode == StorageMode.EXTERNAL && external != null) {
+                        // Asked even when the grant looks held: an already-granted
+                        // request returns at once, a stale belief would strand them.
+                        permissionLauncher.launch(
+                            arrayOf(external.readPermission, external.writePermission),
+                        )
+                    } else {
+                        viewModel.setStorageMode(mode)
+                    }
+                },
+                onDismiss = { showPicker = false },
+            )
+        }
+    }
+}
+
+/**
+ * The two stores, as rows. External is offered only when a provider is actually
+ * installed — dimmed and inert otherwise, because a mode with nothing behind it
+ * empties the app.
+ */
+@Composable
+private fun StorePicker(
+    storage: StorageUiState,
+    onSelect: (StorageMode) -> Unit,
+    onDismiss: () -> Unit,
+) {
+    FullScreenPicker(title = stringResource(R.string.settings_task_store), onDismiss = onDismiss) {
+        Text(
+            text = stringResource(R.string.settings_task_store_hint),
+            style = MaterialTheme.typography.bodyMedium,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+            modifier = Modifier.padding(horizontal = 16.dp, vertical = 4.dp),
+        )
+        Spacer(Modifier.height(8.dp))
+
+        val select: (StorageMode) -> Unit = { chosen ->
+            onSelect(chosen)
+            onDismiss()
+        }
+        val external = storage.external
+        GroupedRow(
+            title = stringResource(R.string.settings_store_own),
+            summary = stringResource(R.string.settings_store_own_hint),
+            position = Position.Top,
+            selected = storage.mode == StorageMode.OWN,
+            leading = { Icon(Icons.Rounded.PhoneAndroid, contentDescription = null) },
+            trailing = if (storage.mode == StorageMode.OWN) {
+                { SelectedCheck() }
+            } else {
+                null
+            },
+            onClick = { select(StorageMode.OWN) },
+        )
+        GroupedRow(
+            title = externalTitle(external, storage.externalLabel),
+            summary = stringResource(
+                if (external == null) {
+                    R.string.settings_store_external_missing
+                } else {
+                    R.string.settings_store_external_hint
+                },
+            ),
+            position = Position.Bottom,
+            selected = storage.mode == StorageMode.EXTERNAL,
+            dimmed = external == null,
+            leading = { Icon(Icons.Rounded.Apps, contentDescription = null) },
+            trailing = if (storage.mode == StorageMode.EXTERNAL) {
+                { SelectedCheck() }
+            } else {
+                null
+            },
+            onClick = if (external != null) ({ select(StorageMode.EXTERNAL) }) else null,
+        )
+        Spacer(Modifier.height(24.dp))
+    }
+}
+
+/** The active store, named the way the picker names it. */
+@Composable
+private fun storeLabel(storage: StorageUiState): String = when (storage.mode) {
+    StorageMode.OWN -> stringResource(R.string.settings_store_own)
+    StorageMode.EXTERNAL -> externalTitle(storage.external, storage.externalLabel)
+}
+
+/** The provider's own app name, its authority, or the generic wording. */
+@Composable
+private fun externalTitle(provider: TaskProvider?, label: String?): String =
+    label ?: provider?.authority ?: stringResource(R.string.settings_store_external)
+
+private fun Context.openAppSettings() {
+    runCatching {
+        startActivity(
+            Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS, "package:$packageName".toUri()),
+        )
+    }
+}

app/src/main/java/de/jeanlucmakiola/agendula/ui/tasklist/TaskListScreen.kt

@@ -44,6 +44,7 @@ import androidx.compose.material.icons.rounded.Add
 import androidx.compose.material.icons.rounded.Check
 import androidx.compose.material.icons.rounded.Checklist
 import androidx.compose.material.icons.rounded.Delete
+import androidx.compose.material.icons.rounded.Edit
 import androidx.compose.material.icons.rounded.ExpandMore
 import androidx.compose.material.icons.rounded.Flag
 import androidx.compose.material3.Checkbox
@@ -97,7 +98,12 @@ import de.jeanlucmakiola.agendula.domain.TaskFilter
 import de.jeanlucmakiola.agendula.domain.TaskSection
 import de.jeanlucmakiola.agendula.domain.TaskSections
 import de.jeanlucmakiola.agendula.ui.common.priorityAccent
+import de.jeanlucmakiola.agendula.ui.lists.ListEditorSheet
+import de.jeanlucmakiola.agendula.ui.lists.ListWriteFailure
 import de.jeanlucmakiola.floret.components.Position
+import de.jeanlucmakiola.floret.components.SnackChip
+import de.jeanlucmakiola.floret.components.SnackChipHeight
+import de.jeanlucmakiola.floret.components.SnackChipMargin
 import de.jeanlucmakiola.floret.time.formatDateTimeCompact
 import de.jeanlucmakiola.floret.components.pastelize
 import de.jeanlucmakiola.floret.components.positionOf
@@ -123,8 +129,22 @@ fun TaskListScreen(
     val state by viewModel.state.collectAsStateWithLifecycle()
     val scrollBehavior = TopAppBarDefaults.exitUntilCollapsedScrollBehavior()
     val content = state as? TaskListUiState.Content
-    val listName = content?.listName
+    val list = content?.list
+    val listName = list?.name
     val listId = (filter as? TaskFilter.OfList)?.listId
+    // Editing is offered for a device-only list. A collection that belongs to an
+    // account is the server's to rename or remove, not ours.
+    var editingList by rememberSaveable { mutableStateOf(false) }
+    val listWriteFailure by viewModel.listWriteFailure.collectAsStateWithLifecycle()
+    val listDeleted by viewModel.listDeleted.collectAsStateWithLifecycle()
+    // The list this screen is about is gone; there is nothing left to show.
+    LaunchedEffect(listDeleted) { if (listDeleted) onBack() }
+    LaunchedEffect(listWriteFailure) {
+        if (listWriteFailure != null) {
+            delay(4_000)
+            viewModel.clearListWriteFailure()
+        }
+    }
     // One add affordance, never two: a real list with the setting on gets a pinned
     // bottom quick-add bar; everything else (incl. smart lists, which have no single
     // target list) gets the floating "New task" button.
@@ -159,6 +179,16 @@ fun TaskListScreen(
                         )
                     }
                 },
+                actions = {
+                    if (list != null && list.isLocal) {
+                        IconButton(onClick = { editingList = true }) {
+                            Icon(
+                                Icons.Rounded.Edit,
+                                contentDescription = stringResource(R.string.list_edit_title),
+                            )
+                        }
+                    }
+                },
                 scrollBehavior = scrollBehavior,
             )
         },
@@ -189,61 +219,50 @@ fun TaskListScreen(
             Box(
                 modifier = Modifier
                     .align(Alignment.BottomStart)
-                    .padding(start = 16.dp, bottom = inner.calculateBottomPadding() + 16.dp)
-                    .height(56.dp),
+                    .padding(
+                        start = SnackChipMargin,
+                        bottom = inner.calculateBottomPadding() + SnackChipMargin,
+                    )
+                    .height(SnackChipHeight),
                 contentAlignment = Alignment.CenterStart,
             ) {
-                UndoChip(
-                    visible = undoTarget != null,
-                    onUndo = {
-                        undoTarget?.let { viewModel.undoDelete(it.taskId) }
-                        undoTarget = null
-                    },
-                )
-            }
-        }
-    }
-}
-
-/**
- * A compact floating "snackchip" for an undoable delete — a rounded pill (not a
- * full-width snackbar) sized to its content, sliding up from the bottom centre.
- */
-@Composable
-private fun UndoChip(visible: Boolean, onUndo: () -> Unit, modifier: Modifier = Modifier) {
-    AnimatedVisibility(
-        visible = visible,
-        enter = slideInVertically { it } + fadeIn(),
-        exit = slideOutVertically { it } + fadeOut(),
-        modifier = modifier,
-    ) {
-        Surface(
-            color = MaterialTheme.colorScheme.surfaceContainerHighest,
-            contentColor = MaterialTheme.colorScheme.onSurface,
-            shape = RoundedCornerShape(50),
-            shadowElevation = 6.dp,
-        ) {
-            Row(
-                verticalAlignment = Alignment.CenterVertically,
-                modifier = Modifier.padding(start = 20.dp, end = 8.dp, top = 6.dp, bottom = 6.dp),
-                horizontalArrangement = Arrangement.spacedBy(12.dp),
-            ) {
-                Text(
-                    text = stringResource(R.string.task_deleted),
-                    style = MaterialTheme.typography.bodyMedium,
-                )
-                TextButton(
-                    onClick = onUndo,
-                    contentPadding = PaddingValues(horizontal = 16.dp, vertical = 6.dp),
-                ) {
-                    Text(
-                        text = stringResource(R.string.undo),
-                        style = MaterialTheme.typography.labelLarge,
+                // One chip, one anchor: the undo receipt takes precedence, and a
+                // refused list write reports itself once the undo window is clear.
+                val failure = listWriteFailure
+                if (undoTarget != null || failure == null) {
+                    SnackChip(
+                        visible = undoTarget != null,
+                        message = stringResource(R.string.task_deleted),
+                        actionLabel = stringResource(R.string.undo),
+                        onAction = {
+                            undoTarget?.let { viewModel.undoDelete(it.taskId) }
+                            undoTarget = null
+                        },
+                    )
+                } else {
+                    SnackChip(
+                        visible = true,
+                        message = stringResource(listWriteFailureMessage(failure)),
                     )
                 }
             }
         }
     }
+
+    if (editingList && list != null) {
+        ListEditorSheet(
+            initial = list,
+            onSave = { name, color -> viewModel.updateList(list.id, name, color) },
+            onDismiss = { editingList = false },
+            onDelete = { viewModel.deleteList(list.id) },
+        )
+    }
+}
+
+/** Wording for a refused list write. */
+private fun listWriteFailureMessage(failure: ListWriteFailure): Int = when (failure) {
+    ListWriteFailure.SAVE -> R.string.list_save_failed
+    ListWriteFailure.DELETE -> R.string.list_delete_failed
 }
 
 @OptIn(ExperimentalMaterial3Api::class, ExperimentalFoundationApi::class)
@@ -806,20 +825,20 @@ private fun SubtaskExpandButton(expanded: Boolean, onToggle: () -> Unit) {
 
 /** A visual row in a flattened section run: a top-level task, or one of its subtasks. */
 private sealed interface ListRow {
-    val key: Long
+    val key: String
 
     data class Parent(val task: Task, val expandable: Boolean, val expanded: Boolean) : ListRow {
-        override val key: Long get() = task.taskId
+        override val key: String get() = task.occurrenceKey
     }
 
     data class Sub(val task: Task) : ListRow {
-        override val key: Long get() = task.taskId
+        override val key: String get() = task.occurrenceKey
     }
 
     /** The inline "add a subtask" row that closes an expanded group. */
     data class AddSub(val parent: Task) : ListRow {
-        // Negative so it never collides with a real (positive) provider task id.
-        override val key: Long get() = -parent.taskId
+        // Prefixed so it never collides with the task row it belongs to.
+        override val key: String get() = "add-${parent.occurrenceKey}"
     }
 }
 

app/src/main/java/de/jeanlucmakiola/agendula/ui/tasklist/TaskListViewModel.kt

@@ -5,14 +5,17 @@ import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
 import de.jeanlucmakiola.agendula.data.prefs.SettingsPrefs
 import de.jeanlucmakiola.agendula.data.tasks.TasksRepository
+import de.jeanlucmakiola.agendula.data.tasks.recoveringFromProviderFailure
 import de.jeanlucmakiola.agendula.domain.Task
 import de.jeanlucmakiola.agendula.domain.TaskFilter
 import de.jeanlucmakiola.agendula.domain.TaskForm
+import de.jeanlucmakiola.agendula.domain.TaskList
+import de.jeanlucmakiola.agendula.ui.lists.ListWriteFailure
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
-import kotlinx.coroutines.flow.catch
+import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.filterNotNull
 import kotlinx.coroutines.flow.flatMapLatest
@@ -28,13 +31,13 @@ sealed interface TaskListUiState {
     data object Failure : TaskListUiState
 
     /**
-     * [listName] is the real list's name when the filter is a
-     * [TaskFilter.OfList] (for the top-bar title), `null` for smart lists —
-     * the screen falls back to the smart label in that case.
+     * [list] is the real list when the filter is a [TaskFilter.OfList] — it
+     * titles the bar and backs the edit action — and `null` for smart lists,
+     * where the screen falls back to the smart label.
      */
     data class Content(
         val tasks: List<Task>,
-        val listName: String? = null,
+        val list: TaskList? = null,
         /** Whether the inline "add a subtask" row shows on expanded groups (M5 setting). */
         val showAddSubtaskRow: Boolean = true,
         /** Whether a real list uses the bottom quick-add bar instead of the FAB. */
@@ -65,8 +68,8 @@ class TaskListViewModel @Inject constructor(
                 val tasks = repository.tasks(f)
                 val content: kotlinx.coroutines.flow.Flow<TaskListUiState> = when (f) {
                     is TaskFilter.OfList ->
-                        combine(tasks, repository.taskLists()) { list, lists ->
-                            TaskListUiState.Content(list, lists.firstOrNull { it.id == f.listId }?.name)
+                        combine(tasks, repository.taskLists()) { rows, lists ->
+                            TaskListUiState.Content(rows, lists.firstOrNull { it.id == f.listId })
                         }
                     is TaskFilter.Smart ->
                         tasks.map { TaskListUiState.Content(it) }
@@ -87,7 +90,10 @@ class TaskListViewModel @Inject constructor(
                     }
                 }
                     .onStart { emit(TaskListUiState.Loading) }
-                    .catch { emit(TaskListUiState.Failure) }
+                    // Recover rather than terminate: a provider hiccup (mid-update,
+                    // permission not yet granted) shows Failure but keeps retrying,
+                    // so the screen heals itself instead of staying stuck.
+                    .recoveringFromProviderFailure { TaskListUiState.Failure }
             }
             .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), TaskListUiState.Loading)
 
@@ -112,6 +118,9 @@ class TaskListViewModel @Inject constructor(
                     combine(ids.map { id -> repository.subtasks(id).map { id to it } }) { it.toMap() }
                 }
             }
+            // Without this an exception here escapes stateIn's coroutine, past
+            // viewModelScope's SupervisorJob, and crashes the process.
+            .recoveringFromProviderFailure { emptyMap() }
             .stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), emptyMap())
 
     /** The screen reports which expanded parents need their children fetched. */
@@ -120,7 +129,7 @@ class TaskListViewModel @Inject constructor(
     fun bind(taskFilter: TaskFilter) { filter.value = taskFilter }
 
     fun toggleComplete(task: Task) = viewModelScope.launch {
-        runCatching { repository.setCompleted(task.taskId, !task.isCompleted) }
+        runCatching { repository.setCompleted(task.taskId, task.occurrenceStart, !task.isCompleted) }
     }
 
     /** Swipe-delete: hide the row now; the screen's snackbar commits or restores it. */
@@ -149,6 +158,36 @@ class TaskListViewModel @Inject constructor(
         runCatching { repository.createTask(TaskForm(title = title, listId = listId)) }
     }
 
+    private val _listWriteFailure = MutableStateFlow<ListWriteFailure?>(null)
+
+    /** Set when a list write is refused; the screen shows it and clears it. */
+    val listWriteFailure: StateFlow<ListWriteFailure?> = _listWriteFailure.asStateFlow()
+
+    private val _listDeleted = MutableStateFlow(false)
+
+    /** Flips once the list this screen shows is really gone, so it can leave. */
+    val listDeleted: StateFlow<Boolean> = _listDeleted.asStateFlow()
+
+    fun clearListWriteFailure() { _listWriteFailure.value = null }
+
+    /** Rename / recolour the list this screen is showing. */
+    fun updateList(listId: Long, name: String, color: Int) = viewModelScope.launch {
+        if (name.isBlank()) return@launch
+        runCatching { repository.updateList(listId, name.trim(), color) }
+            .onFailure { _listWriteFailure.value = ListWriteFailure.SAVE }
+    }
+
+    /**
+     * Delete the list **and its tasks**. The screen navigates away on
+     * [listDeleted], not on the call — leaving first would strand a refusal on a
+     * screen that no longer exists.
+     */
+    fun deleteList(listId: Long) = viewModelScope.launch {
+        runCatching { repository.deleteList(listId) }
+            .onSuccess { _listDeleted.value = true }
+            .onFailure { _listWriteFailure.value = ListWriteFailure.DELETE }
+    }
+
     /** Inline "add subtask" from an expanded list group — files it under [parent]. */
     fun quickAddSubtask(parent: Task, title: String) = viewModelScope.launch {
         if (title.isBlank() || parent.listId <= 0L) return@launch

app/src/main/res/values/strings.xml

@@ -122,7 +122,32 @@
     <string name="lists_header">Lists</string>
     <string name="new_task">New task</string>
     <string name="lists_failure">Could not read your tasks.</string>
-    <string name="lists_empty">No task lists yet. Add one in your tasks app or with the + button.</string>
+    <string name="lists_empty">No task lists yet.</string>
+    <string name="lists_empty_action">Create a list</string>
+
+    <!-- Task lists: create, edit, delete -->
+    <string name="list_add">New list</string>
+    <string name="list_new_title">New list</string>
+    <string name="list_edit_title">Edit list</string>
+    <string name="list_name_hint">List name</string>
+    <string name="list_color">Colour</string>
+    <string name="list_delete">Delete list</string>
+    <string name="list_save_failed">Could not save the list.</string>
+    <string name="list_delete_failed">Could not delete the list.</string>
+    <string name="list_delete_confirm_title">Delete list?</string>
+    <string name="list_delete_confirm_message">“%1$s” and all of its tasks will be deleted. This can\'t be undone.</string>
+    <string name="list_color_mauve">Mauve</string>
+    <string name="list_color_red">Red</string>
+    <string name="list_color_orange">Orange</string>
+    <string name="list_color_amber">Amber</string>
+    <string name="list_color_olive">Olive</string>
+    <string name="list_color_green">Green</string>
+    <string name="list_color_teal">Teal</string>
+    <string name="list_color_cyan">Cyan</string>
+    <string name="list_color_blue">Blue</string>
+    <string name="list_color_indigo">Indigo</string>
+    <string name="list_color_purple">Purple</string>
+    <string name="list_color_pink">Pink</string>
     <string name="smart_today">Today</string>
     <string name="smart_overdue">Overdue</string>
     <string name="smart_upcoming">Upcoming</string>
@@ -190,13 +215,16 @@
     <string name="settings_about_logo_desc">Agendula app icon</string>
     <string name="settings_language">App language</string>
     <string name="settings_language_auto">System default</string>
+    <string name="settings_translate">Help translate</string>
+    <string name="settings_translate_hint">Add or improve a language on Weblate</string>
     <string name="settings_report_problem">Report a problem</string>
     <string name="settings_report_problem_hint">Open the issue tracker</string>
-    <string name="about_source_url" translatable="false">https://gitea.jeanlucmakiola.de/makiolaj/agendula</string>
+    <string name="about_source_url" translatable="false">https://codeberg.org/jlmakiola/agendula</string>
     <string name="crash_report_issue_title">Crash report</string>
-    <string name="report_issue_url" translatable="false">https://gitea.jeanlucmakiola.de/makiolaj/agendula/issues/new</string>
-    <string name="about_license_url" translatable="false">https://gitea.jeanlucmakiola.de/makiolaj/agendula/src/branch/main/LICENSE</string>
+    <string name="report_issue_url" translatable="false">https://codeberg.org/jlmakiola/agendula/issues/new</string>
+    <string name="about_license_url" translatable="false">https://codeberg.org/jlmakiola/agendula/src/branch/main/LICENSE</string>
     <string name="about_support_url" translatable="false">https://ko-fi.com/jeanlucmakiola</string>
+    <string name="about_translate_url" translatable="false">https://weblate.dev.jeanlucmakiola.de/engage/agendula/</string>
     <string name="settings_theme">Theme</string>
     <string name="settings_theme_system">Follow system</string>
     <string name="settings_theme_light">Light</string>
@@ -218,6 +246,37 @@
     <string name="settings_bottom_add_bar">Bottom quick-add bar</string>
     <string name="settings_bottom_add_bar_hint">Add tasks from a bar pinned to the bottom of a list, instead of the floating button</string>
 
+    <string name="onboarding_use_own_store">Use this device\'s storage instead</string>
+
+    <!-- Storage and export -->
+    <string name="settings_section_storage">Storage</string>
+    <string name="settings_storage_subtitle">Where tasks are kept, and export</string>
+    <string name="settings_task_store">Task store</string>
+    <string name="settings_task_store_hint">Each store keeps its own tasks. Switching does not move them across — export first if you want a copy.</string>
+    <string name="settings_store_own">On this device</string>
+    <string name="settings_store_own_hint">Agendula\'s own storage. Nothing else to install.</string>
+    <string name="settings_store_external">Another task app</string>
+    <string name="settings_store_external_hint">Share tasks with the app that syncs them</string>
+    <string name="settings_store_external_missing">No compatible task app is installed</string>
+    <string name="settings_store_permission_denied">Permission denied</string>
+    <string name="settings_store_permission_denied_hint">The other app\'s tasks stay unreachable until you allow access. Tap to open app settings.</string>
+    <string name="settings_export">Export tasks</string>
+    <string name="settings_export_hint">Save your lists as iCalendar files</string>
+    <string name="export_hint">One .ics file per list, readable by other task and calendar apps. The ticked lists go to a folder you pick, or into a single zip.</string>
+    <string name="export_no_lists">No lists to export</string>
+    <string name="export_to_folder">Save to a folder</string>
+    <string name="export_to_zip">Save as a zip file</string>
+    <string name="export_running">Exporting…</string>
+    <plurals name="export_done">
+        <item quantity="one">Exported %1$d list</item>
+        <item quantity="other">Exported %1$d lists</item>
+    </plurals>
+    <string name="export_failed">The export could not be written</string>
+    <string name="export_failed_folder">The chosen folder could not be opened</string>
+    <string name="export_failed_read_only">The chosen folder is not writable</string>
+    <string name="export_failed_create">A file could not be created in the chosen folder</string>
+    <string name="export_failed_access">Access to the chosen location was lost</string>
+
     <!-- Reminder lead times (custom amounts) -->
     <plurals name="reminder_minutes">
         <item quantity="one">%1$d minute before</item>

app/src/main/res/xml/backup_rules.xml

@@ -1,4 +1,22 @@
 <?xml version="1.0" encoding="utf-8"?>
 <full-backup-content>
-    <!-- No file-based backups; settings live in DataStore which is backed up by default. -->
+    <!--
+        Agendula's own task store. Room runs in WAL mode and Auto Backup copies
+        files without checkpointing, so the `-wal` sidecar can hold writes the
+        `.db` alone does not — all three go in together, and the app checkpoints
+        on ON_STOP so a restore is consistent either way.
+
+        Naming any <include> makes everything else excluded by default, so the
+        archived dmfs database (`tasks.db.imported`, kept one release as the
+        import's rollback path) is already left out. An explicit <exclude> for it
+        would be redundant *and* rejected — lint's FullBackupContent check errors
+        on an exclude that sits under no included path.
+
+        Settings live in DataStore, which this exclusion now also covers, so its
+        sharedpref file is listed back in.
+    -->
+    <include domain="database" path="agendula-tasks.db" />
+    <include domain="database" path="agendula-tasks.db-wal" />
+    <include domain="database" path="agendula-tasks.db-shm" />
+    <include domain="file" path="datastore/" />
 </full-backup-content>

app/src/main/res/xml/data_extraction_rules.xml

@@ -1,8 +1,21 @@
 <?xml version="1.0" encoding="utf-8"?>
 <data-extraction-rules>
+    <!--
+        See backup_rules.xml: the WAL sidecars travel with the database, and
+        naming any <include> makes everything else excluded by default — which is
+        what keeps the archived `tasks.db.imported` out without an <exclude> that
+        lint would reject.
+    -->
     <cloud-backup>
-        <!-- Allow DataStore backup, exclude nothing extra. -->
+        <include domain="database" path="agendula-tasks.db" />
+        <include domain="database" path="agendula-tasks.db-wal" />
+        <include domain="database" path="agendula-tasks.db-shm" />
+        <include domain="file" path="datastore/" />
     </cloud-backup>
     <device-transfer>
+        <include domain="database" path="agendula-tasks.db" />
+        <include domain="database" path="agendula-tasks.db-wal" />
+        <include domain="database" path="agendula-tasks.db-shm" />
+        <include domain="file" path="datastore/" />
     </device-transfer>
 </data-extraction-rules>

app/src/test/java/de/jeanlucmakiola/agendula/data/export/TaskExporterTest.kt

@@ -0,0 +1,61 @@
+package de.jeanlucmakiola.agendula.data.export
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+
+/**
+ * The export file name. The user picks the folder, so whatever comes out of here
+ * is what they will be looking at in a file manager a year from now.
+ */
+class TaskExporterTest {
+
+    private fun name(listName: String, id: Long = 3L) = TaskExporter.fileNameFor(listName, id)
+
+    @Test
+    fun `keeps a plain name readable`() {
+        assertThat(name("Groceries")).isEqualTo("Groceries-3.ics")
+    }
+
+    @Test
+    fun `replaces characters a filesystem would reject`() {
+        // SAF can land on FAT32 (an SD card), where these are simply illegal.
+        val result = name("Work / Home: notes?")
+        assertThat(result).doesNotContain("/")
+        assertThat(result).doesNotContain(":")
+        assertThat(result).doesNotContain("?")
+        assertThat(result).endsWith("-3.ics")
+    }
+
+    @Test
+    fun `keeps the id so same-named lists cannot collide`() {
+        // Two accounts may each have a list called "Personal"; without the id one
+        // export would silently overwrite the other.
+        assertThat(name("Personal", 1)).isNotEqualTo(name("Personal", 2))
+    }
+
+    @Test
+    fun `falls back when the name has nothing usable in it`() {
+        assertThat(name("///")).isEqualTo("list-3.ics")
+        assertThat(name("")).isEqualTo("list-3.ics")
+    }
+
+    @Test
+    fun `does not leave dangling separators`() {
+        assertThat(name("  Shopping  ")).isEqualTo("Shopping-3.ics")
+    }
+
+    @Test
+    fun `caps the length`() {
+        // Many filesystems stop at 255 bytes for a name; a pathological list title
+        // should not be the thing that fails an export.
+        assertThat(name("x".repeat(500)).length).isAtMost(80)
+    }
+
+    @Test
+    fun `keeps non-latin names instead of blanking them`() {
+        // isLetterOrDigit is Unicode-aware, so these survive rather than collapsing
+        // to the "list" fallback.
+        assertThat(name("Einkäufe")).isEqualTo("Einkäufe-3.ics")
+        assertThat(name("買い物")).isEqualTo("買い物-3.ics")
+    }
+}

app/src/test/java/de/jeanlucmakiola/agendula/data/tasks/ProviderResolverTest.kt

@@ -0,0 +1,198 @@
+package de.jeanlucmakiola.agendula.data.tasks
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Nested
+import org.junit.jupiter.api.Test
+
+/**
+ * The storage-mode decision, which is the part of [ProviderResolver] with real
+ * consequences: pick wrong for a returning user and the app opens on an empty
+ * store where their tasks used to be.
+ */
+class ProviderResolverTest {
+
+    /**
+     * A [ProviderEnvironment] with no Android in it.
+     *
+     * @param installed authority -> declaring package, i.e. what is on the device.
+     * @param granted permissions this app currently holds.
+     */
+    private class FakeEnvironment(
+        val installed: Map<String, String> = emptyMap(),
+        val granted: Set<String> = emptySet(),
+    ) : ProviderEnvironment {
+        override fun packageDeclaring(authority: String): String? = installed[authority]
+        override fun isGranted(permission: String): Boolean = permission in granted
+        override fun appLabel(packageName: String): String? = packageName
+    }
+
+    private val openTasks = ProviderResolver.EXTERNAL_CANDIDATES.first { it.authority == "org.dmfs.tasks" }
+
+    private fun resolver(
+        installed: Map<String, String> = emptyMap(),
+        granted: Set<String> = emptySet(),
+        mode: StorageMode? = null,
+    ) = ProviderResolver(FakeEnvironment(installed, granted)).apply { storageMode = mode }
+
+    private val openTasksInstalled = mapOf("org.dmfs.tasks" to "org.dmfs.tasks")
+    private val openTasksGranted = setOf(openTasks.readPermission, openTasks.writePermission)
+
+    @Nested
+    inner class OwnStore {
+
+        @Test
+        fun `is readable without anything installed or granted`() {
+            // Guards a real regression: the reminder engine used to gate on
+            // resolve() != null, which is exactly what OWN returns, so every
+            // reminder was cleared the moment our own store became the default.
+            assertThat(resolver(mode = StorageMode.OWN).canReadStore()).isTrue()
+        }
+
+        @Test
+        fun `resolves to no provider at all`() {
+            // Room has no authority and no ContentResolver, so there is nothing
+            // here to resolve — which is the point. Callers that need to tell this
+            // apart from "External, none installed" ask mode().
+            val resolver = resolver(mode = StorageMode.OWN)
+            assertThat(resolver.resolve()).isNull()
+            assertThat(resolver.mode()).isEqualTo(StorageMode.OWN)
+        }
+    }
+
+    @Nested
+    inner class AutoMode {
+
+        @Test
+        fun `a fresh install with nothing else present gets our own store`() {
+            assertThat(resolver().autoMode()).isEqualTo(StorageMode.OWN)
+        }
+
+        @Test
+        fun `an upgrading user who already granted OpenTasks stays on it`() {
+            // Holding a dangerous permission means a previous version asked and they
+            // agreed — the signature of an existing Posture A user. Sending them to
+            // our empty bundled store would read as data loss.
+            val resolver = resolver(installed = openTasksInstalled, granted = openTasksGranted)
+            assertThat(resolver.autoMode()).isEqualTo(StorageMode.EXTERNAL)
+            assertThat(resolver.resolve()?.authority).isEqualTo("org.dmfs.tasks")
+        }
+
+        @Test
+        fun `OpenTasks merely installed is not enough`() {
+            // Someone who has OpenTasks for unrelated reasons, and never granted us
+            // anything, has no data with us there. Our own store is right for them.
+            assertThat(resolver(installed = openTasksInstalled).autoMode()).isEqualTo(StorageMode.OWN)
+        }
+
+        @Test
+        fun `a half-granted external provider does not count`() {
+            val resolver = resolver(
+                installed = openTasksInstalled,
+                granted = setOf(openTasks.readPermission),
+            )
+            assertThat(resolver.autoMode()).isEqualTo(StorageMode.OWN)
+        }
+    }
+
+    @Nested
+    inner class ExplicitChoice {
+
+        @Test
+        fun `overrides the automatic answer in both directions`() {
+            val wouldBeExternal = FakeEnvironment(openTasksInstalled, openTasksGranted)
+
+            val forcedOwn = ProviderResolver(wouldBeExternal).apply { storageMode = StorageMode.OWN }
+            assertThat(forcedOwn.mode()).isEqualTo(StorageMode.OWN)
+            assertThat(forcedOwn.resolve()).isNull()
+
+            val forcedExternal = ProviderResolver(FakeEnvironment()).apply { storageMode = StorageMode.EXTERNAL }
+            assertThat(forcedExternal.mode()).isEqualTo(StorageMode.EXTERNAL)
+            assertThat(forcedExternal.resolve()).isNull()
+        }
+
+        @Test
+        fun `external with no provider installed resolves to nothing`() {
+            // Drives the "install a tasks provider" gate rather than silently
+            // falling back to our own store behind the user's back.
+            assertThat(resolver(mode = StorageMode.EXTERNAL).resolve()).isNull()
+        }
+
+        @Test
+        fun `external is unreadable until a provider is installed and granted`() {
+            assertThat(resolver(mode = StorageMode.EXTERNAL).canReadStore()).isFalse()
+            assertThat(
+                resolver(installed = openTasksInstalled, mode = StorageMode.EXTERNAL).canReadStore(),
+            ).isFalse()
+            assertThat(
+                resolver(
+                    installed = openTasksInstalled,
+                    granted = openTasksGranted,
+                    mode = StorageMode.EXTERNAL,
+                ).canReadStore(),
+            ).isTrue()
+        }
+
+        @Test
+        fun `external still requires the runtime permission`() {
+            val resolver = resolver(installed = openTasksInstalled, mode = StorageMode.EXTERNAL)
+            val provider = resolver.resolve()
+            assertThat(provider).isNotNull()
+            assertThat(resolver.hasPermission(provider!!)).isFalse()
+        }
+    }
+
+    @Nested
+    inner class ExternalCandidates {
+
+        @Test
+        fun `prefer OpenTasks over tasks_org when both are installed`() {
+            val resolver = resolver(
+                installed = mapOf(
+                    "org.dmfs.tasks" to "org.dmfs.tasks",
+                    "org.tasks.opentasks" to "org.tasks",
+                ),
+                mode = StorageMode.EXTERNAL,
+            )
+            assertThat(resolver.resolve()?.authority).isEqualTo("org.dmfs.tasks")
+        }
+
+        @Test
+        fun `fall through to tasks_org when OpenTasks is absent`() {
+            val resolver = resolver(
+                installed = mapOf("org.tasks.opentasks" to "org.tasks"),
+                mode = StorageMode.EXTERNAL,
+            )
+            assertThat(resolver.resolve()?.packageName).isEqualTo("org.tasks")
+        }
+
+        @Test
+        fun `a mode change notifies listeners once, and only on a real change`() {
+            // What store observers hang off: a live flow is bound to one store, so
+            // it has to be told when the store underneath it is swapped.
+            val resolver = resolver(mode = StorageMode.OWN)
+            var fired = 0
+            val handle = resolver.onModeChanged { fired++ }
+
+            resolver.storageMode = StorageMode.OWN
+            assertThat(fired).isEqualTo(0)
+
+            resolver.storageMode = StorageMode.EXTERNAL
+            assertThat(fired).isEqualTo(1)
+
+            handle.close()
+            resolver.storageMode = StorageMode.OWN
+            assertThat(fired).isEqualTo(1)
+        }
+
+        @Test
+        fun `never name an authority of ours`() {
+            // EXTERNAL must mean "somebody else's store", and Agendula publishes no
+            // provider at all any more.
+            assertThat(
+                ProviderResolver.EXTERNAL_CANDIDATES.none {
+                    it.authority.startsWith("de.jeanlucmakiola")
+                },
+            ).isTrue()
+        }
+    }
+}

app/src/test/java/de/jeanlucmakiola/agendula/data/tasks/TaskMapperTest.kt

@@ -36,7 +36,6 @@ class TaskMapperTest {
 
         val task = TaskMapper.task(reader)
 
-        assertThat(task.id).isEqualTo(42L)
         assertThat(task.taskId).isEqualTo(7L)
         assertThat(task.listId).isEqualTo(3L)
         assertThat(task.title).isEqualTo("Buy milk")
@@ -50,6 +49,65 @@ class TaskMapperTest {
         assertThat(task.isSubtask).isTrue()
     }
 
+    @Test
+    fun `an occurrence is identified by its recurrence-id anchor`() {
+        fun occurrence(columns: Map<String, Any?>) =
+            TaskMapper.task(MapColumnReader(columns + (Tasks.RRULE to "FREQ=DAILY")))
+
+        // instance_original_time is the provider's own RECURRENCE-ID and wins.
+        val anchored = occurrence(
+            mapOf(
+                Instances.TASK_ID to 7L,
+                Instances.INSTANCE_ORIGINAL_TIME to 500L,
+                Instances.INSTANCE_START to 900L,
+            ),
+        )
+        assertThat(anchored.occurrenceStart?.toEpochMilliseconds()).isEqualTo(500L)
+        assertThat(anchored.occurrenceKey).isEqualTo("7@500")
+
+        // Older provider schemas omit it; the occurrence's start reconstructs it.
+        val byStart = occurrence(mapOf(Instances.TASK_ID to 7L, Instances.INSTANCE_START to 900L))
+        assertThat(byStart.occurrenceStart?.toEpochMilliseconds()).isEqualTo(900L)
+
+        // A series carrying only DUE anchors on the due date instead.
+        val byDue = occurrence(mapOf(Instances.TASK_ID to 7L, Instances.INSTANCE_DUE to 1_200L))
+        assertThat(byDue.occurrenceStart?.toEpochMilliseconds()).isEqualTo(1_200L)
+    }
+
+    @Test
+    fun `a non-recurring task has no occurrence anchor and keys by task id`() {
+        val task = TaskMapper.task(
+            MapColumnReader(mapOf(Tasks.ID to 4L, Instances.INSTANCE_START to 500L)),
+        )
+        assertThat(task.occurrenceStart).isNull()
+        assertThat(task.occurrenceKey).isEqualTo("4")
+    }
+
+    @Test
+    fun `recurrence is detected from rrule when is_recurring is absent`() {
+        // tasks.org's bundled provider is DB 22 and has no `is_recurring` column;
+        // reading it alone would report the series as one-off and send its edits
+        // to the master row, re-anchoring the whole thing.
+        val task = TaskMapper.task(
+            MapColumnReader(mapOf(Tasks.ID to 1L, Tasks.RRULE to "FREQ=WEEKLY;BYDAY=MO")),
+        )
+        assertThat(task.isRecurring).isTrue()
+    }
+
+    @Test
+    fun `recurrence is detected from rdate alone`() {
+        val task = TaskMapper.task(
+            MapColumnReader(mapOf(Tasks.ID to 1L, Tasks.RDATE to "20260720T090000Z")),
+        )
+        assertThat(task.isRecurring).isTrue()
+    }
+
+    @Test
+    fun `a plain task is not recurring`() {
+        val task = TaskMapper.task(MapColumnReader(mapOf(Tasks.ID to 1L, Tasks.TITLE to "One-off")))
+        assertThat(task.isRecurring).isFalse()
+    }
+
     @Test
     fun `falls back to instance id when task_id missing, and list color when no task color`() {
         val task = TaskMapper.task(

app/src/test/java/de/jeanlucmakiola/agendula/data/tasks/TaskWriteMapperTest.kt

@@ -85,6 +85,57 @@ class TaskWriteMapperTest {
         assertThat(values[Tasks.TZ]).isNull()
     }
 
+    @Test
+    fun `all-day timestamps are pinned to UTC midnight`() {
+        // 2026-07-20T22:00Z — i.e. local midnight on the 21st in Berlin (UTC+2).
+        // The provider resolves all-day dates against UTC, so storing this as-is
+        // would land the task on the 20th for anyone reading it back.
+        val berlinMidnight = Instant.fromEpochMilliseconds(1_784_412_000_000L)
+        val values = TaskWriteMapper.taskValues(
+            TaskForm(title = "Holiday", listId = 1L, start = berlinMidnight, due = berlinMidnight, isAllDay = true),
+            tzId = "Europe/Berlin",
+        )
+
+        val dayMs = 24L * 60 * 60 * 1000
+        assertThat(values[Tasks.DUE] as Long % dayMs).isEqualTo(0L)
+        assertThat(values[Tasks.DTSTART] as Long % dayMs).isEqualTo(0L)
+    }
+
+    @Test
+    fun `timed timestamps are written untouched`() {
+        val at = Instant.fromEpochMilliseconds(1_784_412_345_678L)
+        val values = TaskWriteMapper.taskValues(
+            TaskForm(title = "Standup", listId = 1L, start = at, due = at),
+            tzId = "Europe/Berlin",
+        )
+        assertThat(values[Tasks.DTSTART]).isEqualTo(1_784_412_345_678L)
+        assertThat(values[Tasks.DUE]).isEqualTo(1_784_412_345_678L)
+    }
+
+    @Test
+    fun `duration is always cleared so it cannot collide with due`() {
+        // The provider validates the *merged* row and throws "Only one of DUE or
+        // DURATION must be supplied" if the stored row still carries a duration.
+        val values = TaskWriteMapper.taskValues(
+            TaskForm(title = "x", listId = 1L, due = Instant.fromEpochMilliseconds(5_000L)),
+            tzId = "UTC",
+        )
+        assertThat(values.containsKey(Tasks.DURATION)).isTrue()
+        assertThat(values[Tasks.DURATION]).isNull()
+    }
+
+    @Test
+    fun `instance values drop list and parent, which an override cannot express`() {
+        val form = TaskForm(title = "x", listId = 4L, parentId = 7L, due = Instant.fromEpochMilliseconds(1_000L))
+        val values = TaskWriteMapper.instanceValues(form, tzId = "UTC")
+
+        assertThat(values.containsKey(Tasks.LIST_ID)).isFalse()
+        assertThat(values.containsKey(Tasks.PARENT_ID)).isFalse()
+        // …but still carries the edit itself.
+        assertThat(values[Tasks.TITLE]).isEqualTo("x")
+        assertThat(values[Tasks.DUE]).isEqualTo(1_000L)
+    }
+
     @Test
     fun `completion sets status, percent and timestamp, un-completion clears them`() {
         val done = TaskWriteMapper.completionValues(completed = true, nowMillis = 999L)
@@ -97,6 +148,22 @@ class TaskWriteMapperTest {
         assertThat(undone[Tasks.COMPLETED]).isNull()
     }
 
+    @Test
+    fun `alarm carries every column the provider's validator demands`() {
+        val values = TaskWriteMapper.alarmValues(taskId = 12L, minutesBeforeDue = 30)
+
+        assertThat(values[TasksContract.Properties.TASK_ID]).isEqualTo(12L)
+        assertThat(values[TasksContract.Properties.MIMETYPE])
+            .isEqualTo("vnd.android.cursor.item/alarm")
+        assertThat(values[TasksContract.Alarm.MINUTES_BEFORE]).isEqualTo(30)
+        // REFERENCE must be present and non-negative, ALARM_TYPE present and
+        // non-zero (0 is excluded from the provider's has_alarms count).
+        assertThat(values[TasksContract.Alarm.REFERENCE]).isEqualTo(TasksContract.Alarm.REFERENCE_DUE)
+        assertThat(values[TasksContract.Alarm.ALARM_TYPE]).isEqualTo(TasksContract.Alarm.TYPE_MESSAGE)
+        // property_id must be absent or the insert is rejected.
+        assertThat(values.containsKey(TasksContract.Properties.PROPERTY_ID)).isFalse()
+    }
+
     @Test
     fun `local list uses the LOCAL account`() {
         val values = TaskWriteMapper.localListValues("Inbox", 0x123)