diff --git a/.gitea/workflows/ci.yaml b/.gitea/workflows/ci.yaml
index b0f8513..1e68c6c 100644
--- a/.gitea/workflows/ci.yaml
+++ b/.gitea/workflows/ci.yaml
@@ -26,6 +26,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+          with:
+            submodules: recursive
         with:
           # Full history so the base..HEAD diff below has a merge-base.
           fetch-depth: 0
diff --git a/.gitea/workflows/release.yaml b/.gitea/workflows/release.yaml
index 635c6a8..82826ea 100644
--- a/.gitea/workflows/release.yaml
+++ b/.gitea/workflows/release.yaml
@@ -33,6 +33,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+          with:
+            submodules: recursive
 
       - name: Resolve version and whether it is a new release
         id: v
@@ -82,6 +84,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+          with:
+            submodules: recursive
 
       - name: Setup Java
         uses: actions/setup-java@v4
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..103c066
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "floret-kit"]
+	path = floret-kit
+	url = https://gitea.jeanlucmakiola.de/makiolaj/floret-kit.git
diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index 46440cf..29669c5 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -159,6 +159,7 @@ dependencies {
     implementation(libs.androidx.glance.material3)
 
     implementation(libs.kotlinx.datetime)
+    implementation("de.jeanlucmakiola.floret:core-time")
     implementation(libs.kotlinx.coroutines.core)
 
     debugImplementation(libs.androidx.ui.tooling)
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt
index 8e02288..bc650d3 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarDataSource.kt
@@ -1,5 +1,7 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
+import de.jeanlucmakiola.floret.time.toEpochMillis
+import de.jeanlucmakiola.floret.time.toKotlinInstantFromEpochMillis
 import android.Manifest
 import android.content.ContentResolver
 import android.content.ContentUris
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepositoryImpl.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepositoryImpl.kt
index bde325a..b7bedde 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepositoryImpl.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepositoryImpl.kt
@@ -1,5 +1,6 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
+import de.jeanlucmakiola.floret.time.toEpochMillis
 import de.jeanlucmakiola.calendula.data.di.IoDispatcher
 import de.jeanlucmakiola.calendula.data.prefs.CalendarPrefs
 import de.jeanlucmakiola.calendula.data.prefs.SettingsPrefs
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapper.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapper.kt
index 4a59358..31cf534 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapper.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/EventDetailMapper.kt
@@ -1,5 +1,6 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
+import de.jeanlucmakiola.floret.time.toKotlinInstantFromEpochMillis
 import android.provider.CalendarContract
 import android.util.Log
 import de.jeanlucmakiola.calendula.domain.AccessLevel
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/IcsExportMapper.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/IcsExportMapper.kt
index 817cff3..ce8befa 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/IcsExportMapper.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/IcsExportMapper.kt
@@ -1,5 +1,6 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
+import de.jeanlucmakiola.floret.time.toKotlinInstantFromEpochMillis
 import de.jeanlucmakiola.calendula.domain.EventStatus
 import de.jeanlucmakiola.calendula.domain.ics.IcsEvent
 import de.jeanlucmakiola.calendula.domain.ics.deriveIcsUid
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/InstanceMapper.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/InstanceMapper.kt
index 263300b..6c72def 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/InstanceMapper.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/InstanceMapper.kt
@@ -1,5 +1,6 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
+import de.jeanlucmakiola.floret.time.toKotlinInstantFromEpochMillis
 import android.util.Log
 import de.jeanlucmakiola.calendula.domain.EventInstance
 
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/SearchMapper.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/SearchMapper.kt
index 4c09781..56ba635 100644
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/SearchMapper.kt
+++ b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/SearchMapper.kt
@@ -1,5 +1,6 @@
 package de.jeanlucmakiola.calendula.data.calendar
 
+import de.jeanlucmakiola.floret.time.toKotlinInstantFromEpochMillis
 import de.jeanlucmakiola.calendula.domain.EventInstance
 import de.jeanlucmakiola.calendula.domain.ics.parseRfc2445DurationMillis
 
diff --git a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/TimeBridge.kt b/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/TimeBridge.kt
deleted file mode 100644
index 757c7a8..0000000
--- a/app/src/main/java/de/jeanlucmakiola/calendula/data/calendar/TimeBridge.kt
+++ /dev/null
@@ -1,7 +0,0 @@
-package de.jeanlucmakiola.calendula.data.calendar
-
-import kotlin.time.Instant
-
-fun Long.toKotlinInstantFromEpochMillis(): Instant = Instant.fromEpochMilliseconds(this)
-
-fun Instant.toEpochMillis(): Long = toEpochMilliseconds()
diff --git a/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/TimeBridgeTest.kt b/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/TimeBridgeTest.kt
deleted file mode 100644
index 08de313..0000000
--- a/app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/TimeBridgeTest.kt
+++ /dev/null
@@ -1,26 +0,0 @@
-package de.jeanlucmakiola.calendula.data.calendar
-
-import com.google.common.truth.Truth.assertThat
-import kotlin.time.Instant
-import org.junit.jupiter.api.Test
-
-class TimeBridgeTest {
-
-    @Test
-    fun `epoch millis round-trips through Instant`() {
-        val original = 1_717_840_800_000L // 2024-06-08T10:00:00Z
-        val instant = original.toKotlinInstantFromEpochMillis()
-        assertThat(instant.toEpochMillis()).isEqualTo(original)
-    }
-
-    @Test
-    fun `zero millis maps to Instant epoch`() {
-        assertThat(0L.toKotlinInstantFromEpochMillis()).isEqualTo(Instant.fromEpochMilliseconds(0L))
-    }
-
-    @Test
-    fun `negative epoch millis is supported`() {
-        val original = -1_000_000L
-        assertThat(original.toKotlinInstantFromEpochMillis().toEpochMillis()).isEqualTo(original)
-    }
-}
diff --git a/docs/fdroid-official/de.jeanlucmakiola.calendula.yml b/docs/fdroid-official/de.jeanlucmakiola.calendula.yml
index 45a7a3e..86b95a7 100644
--- a/docs/fdroid-official/de.jeanlucmakiola.calendula.yml
+++ b/docs/fdroid-official/de.jeanlucmakiola.calendula.yml
@@ -43,11 +43,21 @@ Builds:
     versionCode: 20705
     commit: v2.7.5
     subdir: app
+    submodules: true
     gradle:
       - yes
     # No NDK / no flavors. The release buildType applies a signingConfig only
     # when key.properties exists; on the buildserver it does not, so this
     # produces the unsigned APK F-Droid compares against our binary.
+    #
+    # submodules: true — REQUIRED from v2.11.0 onward, where the build pulls
+    # shared code from the `floret-kit` git submodule via a Gradle composite
+    # build (`includeBuild("floret-kit")`). Without it F-Droid checks out an
+    # empty floret-kit/ and the from-source build fails, stalling publishing.
+    # Inert for v2.7.5 (no submodule yet); kept here so AutoUpdateMode copies it
+    # onto every auto-generated future build entry. The kit is plain-Kotlin and
+    # carries no foojay toolchain resolver, so it clears the same reproducibility
+    # bar (enforced by scripts/check_reproducible_release.sh).
 
 # SHA-256 of our app signing certificate (public; embedded in every published
 # APK). Locks F-Droid to publish only binaries signed with our key.
diff --git a/floret-kit b/floret-kit
new file mode 160000
index 0000000..554d536
--- /dev/null
+++ b/floret-kit
@@ -0,0 +1 @@
+Subproject commit 554d536b2fb678f670069648e156cc2c3b015bea
diff --git a/scripts/check_reproducible_release.sh b/scripts/check_reproducible_release.sh
index 33fc4cb..7011401 100755
--- a/scripts/check_reproducible_release.sh
+++ b/scripts/check_reproducible_release.sh
@@ -34,8 +34,15 @@ else
 fi
 
 # 2. The foojay toolchain resolver must not be present in any Gradle script.
+#    This includes the floret-kit submodule: it's an included build (composite
+#    build via `includeBuild`), so F-Droid evaluates its Gradle scripts too when
+#    building from source — the same offline-scanner bar applies to it.
 gradle_files=("$SETTINGS" "$APP")
 [ -f build.gradle.kts ] && gradle_files+=(build.gradle.kts)
+if [ -d floret-kit ]; then
+  while IFS= read -r f; do gradle_files+=("$f"); done \
+    < <(find floret-kit -name '*.gradle.kts' -not -path '*/build/*')
+fi
 if grep -qi 'foojay' "${gradle_files[@]}"; then
   echo "ERROR: foojay toolchain resolver found in: $(grep -li foojay "${gradle_files[@]}" | tr '\n' ' ')" >&2
   echo "       F-Droid's source scanner rejects org.gradle.toolchains.foojay-resolver" >&2
diff --git a/settings.gradle.kts b/settings.gradle.kts
index 450da9a..39d8e55 100644
--- a/settings.gradle.kts
+++ b/settings.gradle.kts
@@ -22,3 +22,4 @@ dependencyResolutionManagement {
 
 rootProject.name = "Calendula"
 include(":app")
+includeBuild("floret-kit")