docs(03-01): complete PostgreSQL store and migration infrastructure plan

- Add 03-01-SUMMARY.md with full execution record
- Update STATE.md: advance to plan 2, record metrics and decisions
- Update ROADMAP.md: phase 03 in progress (1/2 plans complete)
- Update REQUIREMENTS.md: mark DB-01 and DB-03 complete

.planning/REQUIREMENTS.md

@@ -22,9 +22,9 @@ Requirements for this milestone. Each maps to roadmap phases.
 
 ### Database
 
-- [ ] **DB-01**: PostgreSQL is supported as an alternative to SQLite via pgx v5 driver
+- [x] **DB-01**: PostgreSQL is supported as an alternative to SQLite via pgx v5 driver
 - [ ] **DB-02**: Database backend is selected via DATABASE_URL env var (present = PostgreSQL, absent = SQLite with DB_PATH)
-- [ ] **DB-03**: Existing SQLite users can upgrade without data loss (baseline migration represents current schema)
+- [x] **DB-03**: Existing SQLite users can upgrade without data loss (baseline migration represents current schema)
 
 ### Bulk Actions
 
@@ -98,9 +98,9 @@ Which phases cover which requirements. Updated during roadmap creation.
 | REFAC-01 | Phase 2 | Complete |
 | REFAC-02 | Phase 2 | Complete |
 | REFAC-03 | Phase 2 | Complete |
-| DB-01 | Phase 3 | Pending |
+| DB-01 | Phase 3 | Complete |
 | DB-02 | Phase 3 | Pending |
-| DB-03 | Phase 3 | Pending |
+| DB-03 | Phase 3 | Complete |
 | BULK-01 | Phase 4 | Pending |
 | BULK-02 | Phase 4 | Pending |
 | SRCH-01 | Phase 4 | Pending |

.planning/ROADMAP.md

@@ -61,7 +61,7 @@ Plans:
 **Plans**: 2 plans
 
 Plans:
-- [ ] 03-01-PLAN.md — Create PostgresStore (9 Store methods), PostgreSQL migration files, rename RunMigrations to RunSQLiteMigrations, add RunPostgresMigrations
+- [x] 03-01-PLAN.md — Create PostgresStore (9 Store methods), PostgreSQL migration files, rename RunMigrations to RunSQLiteMigrations, add RunPostgresMigrations
 - [ ] 03-02-PLAN.md — Wire DATABASE_URL branching in main.go, fix cross-dialect UNIQUE detection, add Docker Compose postgres profiles, create build-tagged test helper
 
 ### Phase 4: UX Improvements

.planning/STATE.md

@@ -2,14 +2,14 @@
 gsd_state_version: 1.0
 milestone: v1.0
 milestone_name: milestone
-status: Ready to plan
-stopped_at: Phase 3 context gathered
-last_updated: "2026-03-24T07:46:57.289Z"
+status: Ready to execute
+stopped_at: Completed 03-01-PLAN.md
+last_updated: "2026-03-24T08:10:37.889Z"
 progress:
   total_phases: 4
   completed_phases: 2
-  total_plans: 4
-  completed_plans: 4
+  total_plans: 6
+  completed_plans: 5
 ---
 
 # Project State
@@ -19,12 +19,12 @@ progress:
 See: .planning/PROJECT.md (updated 2026-03-23)
 
 **Core value:** Reliable, persistent visibility into which services need updating — data never disappears, and the dashboard is the one place you trust to show the full picture.
-**Current focus:** Phase 02 — backend-refactor
+**Current focus:** Phase 03 — postgresql-support
 
 ## Current Position
 
-Phase: 3
-Plan: Not started
+Phase: 03 (postgresql-support) — EXECUTING
+Plan: 2 of 2
 
 ## Performance Metrics
 
@@ -50,6 +50,7 @@ Plan: Not started
 | Phase 01-data-integrity P02 | 7 | 2 tasks | 2 files |
 | Phase 02-backend-refactor P01 | 7min | 2 tasks | 7 files |
 | Phase 02-backend-refactor P02 | 3min | 2 tasks | 4 files |
+| Phase 03-postgresql-support P01 | 3min | 2 tasks | 7 files |
 
 ## Accumulated Context
 
@@ -70,6 +71,8 @@ Recent decisions affecting current work:
 - [Phase 02-backend-refactor]: golang-migrate v4.19.1 database/sqlite sub-package confirmed to use modernc.org/sqlite (no CGO); single 0001 baseline migration uses CREATE TABLE IF NOT EXISTS for backward compatibility
 - [Phase 02-backend-refactor]: Option B for test store access: internal helpers in export_test.go (TestUpsertEvent, TestGetUpdatesMap) instead of exported Store() accessor - keeps store field unexported
 - [Phase 02-backend-refactor]: NewTestServer pattern: each test gets its own in-memory SQLite DB (RunMigrations + NewSQLiteStore + NewServer) - eliminates shared global state between tests
+- [Phase 03-postgresql-support]: PostgresStore uses *sql.DB via pgx/v5/stdlib adapter with no mutex; TEXT timestamps match SQLiteStore scan logic
+- [Phase 03-postgresql-support]: CreateTag uses RETURNING id in PostgresStore (pgx does not support LastInsertId); AssignTag uses ON CONFLICT DO UPDATE
 
 ### Pending Todos
 
@@ -82,6 +85,6 @@ None yet.
 
 ## Session Continuity
 
-Last session: 2026-03-24T07:46:57.286Z
-Stopped at: Phase 3 context gathered
-Resume file: .planning/phases/03-postgresql-support/03-CONTEXT.md
+Last session: 2026-03-24T08:10:37.887Z
+Stopped at: Completed 03-01-PLAN.md
+Resume file: None

.planning/phases/03-postgresql-support/03-01-SUMMARY.md

@@ -0,0 +1,93 @@
+---
+phase: 03-postgresql-support
+plan: "01"
+subsystem: persistence
+tags: [postgresql, store, migration, pgx]
+dependency_graph:
+  requires: []
+  provides: [PostgresStore, RunPostgresMigrations, RunSQLiteMigrations]
+  affects: [pkg/diunwebhook/migrate.go, pkg/diunwebhook/postgres_store.go]
+tech_stack:
+  added: [github.com/jackc/pgx/v5 v5.9.1, golang-migrate pgx/v5 driver]
+  patterns: [Store interface implementation, golang-migrate embedded migrations, pgx/v5 stdlib adapter]
+key_files:
+  created:
+    - pkg/diunwebhook/postgres_store.go
+    - pkg/diunwebhook/migrations/postgres/0001_initial_schema.up.sql
+    - pkg/diunwebhook/migrations/postgres/0001_initial_schema.down.sql
+  modified:
+    - pkg/diunwebhook/migrate.go
+    - pkg/diunwebhook/export_test.go
+    - go.mod
+    - go.sum
+decisions:
+  - "PostgresStore uses *sql.DB via pgx/v5/stdlib adapter — no native pgx pool, consistent with SQLiteStore pattern"
+  - "No mutex in PostgresStore — PostgreSQL handles concurrent writes natively (unlike SQLite)"
+  - "Timestamps stored as TEXT in PostgreSQL schema — matches SQLite scan logic, avoids TIMESTAMPTZ type divergence"
+  - "CreateTag uses RETURNING id instead of LastInsertId — pgx driver does not support LastInsertId"
+  - "AssignTag uses ON CONFLICT (image) DO UPDATE instead of INSERT OR REPLACE — standard PostgreSQL upsert"
+  - "Both migration runners compiled into same binary — no build tags needed (both drivers always present)"
+metrics:
+  duration: "~2.5 minutes"
+  completed: "2026-03-24T08:09:42Z"
+  tasks_completed: 2
+  files_changed: 7
+---
+
+# Phase 03 Plan 01: PostgreSQL Store and Migration Infrastructure Summary
+
+PostgresStore implementing all 9 Store interface methods using pgx/v5 stdlib adapter, plus PostgreSQL migration infrastructure with RunPostgresMigrations and renamed RunSQLiteMigrations.
+
+## What Was Built
+
+### PostgresStore (pkg/diunwebhook/postgres_store.go)
+Full implementation of the Store interface for PostgreSQL:
+- `NewPostgresStore` constructor with connection pool: `MaxOpenConns(25)`, `MaxIdleConns(5)`, `ConnMaxLifetime(5m)`
+- All 9 methods: `UpsertEvent`, `GetUpdates`, `AcknowledgeUpdate`, `ListTags`, `CreateTag`, `DeleteTag`, `AssignTag`, `UnassignTag`, `TagExists`
+- PostgreSQL-native SQL: `$1..$15` positional params, `NOW()`, `RETURNING id`, `ON CONFLICT DO UPDATE`
+- No `sync.Mutex` — PostgreSQL handles concurrent writes natively
+
+### PostgreSQL Migrations (pkg/diunwebhook/migrations/postgres/)
+- `0001_initial_schema.up.sql`: Creates same 3 tables as SQLite (`updates`, `tags`, `tag_assignments`); uses `SERIAL PRIMARY KEY` for `tags.id`; timestamps remain `TEXT` to match scan logic
+- `0001_initial_schema.down.sql`: Drops all 3 tables in dependency order
+
+### Updated migrate.go
+- `RunMigrations` renamed to `RunSQLiteMigrations`
+- `RunPostgresMigrations` added using `pgxmigrate` driver with `"pgx5"` database name
+- Second `//go:embed migrations/postgres` directive added for `postgresMigrations`
+
+## Decisions Made
+
+| Decision | Rationale |
+|----------|-----------|
+| TEXT timestamps in PostgreSQL schema | Avoids scan divergence with SQLiteStore; both stores parse RFC3339 strings identically |
+| RETURNING id in CreateTag | pgx driver does not implement `LastInsertId`; `RETURNING` is the PostgreSQL-idiomatic approach |
+| ON CONFLICT (image) DO UPDATE in AssignTag | Replaces SQLite's `INSERT OR REPLACE`; functionally equivalent upsert in standard SQL |
+| No mutex in PostgresStore | PostgreSQL connection pool + MVCC handles concurrency; mutex would serialize unnecessarily |
+| Both drivers compiled into binary | Simpler than build tags; binary size cost acceptable for a server binary |
+
+## Deviations from Plan
+
+### Auto-fixed Issues
+
+**1. [Rule 1 - Bug] Updated export_test.go to use renamed function**
+- **Found during:** Task 1 verification
+- **Issue:** `go vet ./pkg/diunwebhook/` failed because `export_test.go` still referenced `RunMigrations` (renamed to `RunSQLiteMigrations`). The plan's acceptance criteria requires `go vet` to exit 0, which takes precedence over the instruction to defer export_test.go changes to Plan 02.
+- **Fix:** Updated both `NewTestServer` and `NewTestServerWithSecret` in `export_test.go` to call `RunSQLiteMigrations`
+- **Files modified:** `pkg/diunwebhook/export_test.go`
+- **Commit:** 95b64b4
+
+## Verification Results
+
+- `go build ./pkg/diunwebhook/` exits 0
+- `go vet ./pkg/diunwebhook/` exits 0
+- PostgreSQL migration UP contains `SERIAL PRIMARY KEY`, all 3 tables
+- PostgreSQL migration DOWN contains `DROP TABLE IF EXISTS` for all 3 tables
+- `go.mod` contains `github.com/jackc/pgx/v5 v5.9.1`
+- `migrate.go` exports both `RunSQLiteMigrations` and `RunPostgresMigrations`
+
+## Known Stubs
+
+None — this plan creates implementation code, not UI stubs.
+
+## Self-Check: PASSED