docs(01-01): complete UPSERT + FK enforcement plan

- Create 01-01-SUMMARY.md documenting both bug fixes and test addition
- Advance plan counter to 2/2 in STATE.md
- Record decisions and metrics in STATE.md
- Update ROADMAP.md plan progress (1/2 summaries)
- Mark requirements DATA-01 and DATA-02 complete

.planning/phases/01-data-integrity/01-01-SUMMARY.md

@@ -0,0 +1,81 @@
+---
+phase: 01-data-integrity
+plan: "01"
+subsystem: backend/storage
+tags: [sqlite, bug-fix, data-integrity, upsert, foreign-keys]
+dependency_graph:
+  requires: []
+  provides: [DATA-01, DATA-02]
+  affects: [pkg/diunwebhook/diunwebhook.go]
+tech_stack:
+  added: []
+  patterns: [SQLite UPSERT (ON CONFLICT DO UPDATE), PRAGMA foreign_keys = ON]
+key_files:
+  created: []
+  modified:
+    - pkg/diunwebhook/diunwebhook.go
+    - pkg/diunwebhook/diunwebhook_test.go
+decisions:
+  - "Use named-column INSERT with ON CONFLICT(image) DO UPDATE SET (UPSERT) instead of INSERT OR REPLACE to preserve tag_assignments child rows"
+  - "Enable PRAGMA foreign_keys = ON immediately after SetMaxOpenConns(1) so all connections (single-connection pool) enforce FK constraints"
+metrics:
+  duration: "2 minutes"
+  completed_date: "2026-03-23"
+  tasks_completed: 2
+  files_modified: 2
+---
+
+# Phase 01 Plan 01: Fix SQLite Data-Destruction Bugs (UPSERT + FK Enforcement) Summary
+
+**One-liner:** SQLite UPSERT replaces INSERT OR REPLACE to preserve tag_assignments on re-insert, and PRAGMA foreign_keys = ON enables ON DELETE CASCADE for tag deletion.
+
+## What Was Built
+
+Fixed two silent data-destruction bugs in the SQLite persistence layer:
+
+**Bug DATA-01 (INSERT OR REPLACE destroying tags):** SQLite's `INSERT OR REPLACE` is implemented as DELETE + INSERT. The DELETE fired `ON DELETE CASCADE` on `tag_assignments.image`, silently removing the tag assignment every time a new DIUN event arrived for an already-tagged image. Fixed by replacing the statement with a proper UPSERT (`INSERT INTO ... ON CONFLICT(image) DO UPDATE SET`) that only updates the non-key columns, leaving `tag_assignments` untouched.
+
+**Bug DATA-02 (FK enforcement disabled):** SQLite disables foreign key enforcement by default. `PRAGMA foreign_keys = ON` was never executed, so `ON DELETE CASCADE` on `tag_assignments.tag_id` did not fire when a tag was deleted. Fixed by executing the pragma immediately after `db.SetMaxOpenConns(1)` in `InitDB()`, before any DDL statements.
+
+## Tasks Completed
+
+| Task | Name | Commit | Files |
+|------|------|--------|-------|
+| 1 | Replace INSERT OR REPLACE with UPSERT + add PRAGMA FK enforcement | 7edbaad | pkg/diunwebhook/diunwebhook.go |
+| 2 | Add regression test TestUpdateEvent_PreservesTagOnUpsert | e2d388c | pkg/diunwebhook/diunwebhook_test.go |
+
+## Decisions Made
+
+1. **Named-column UPSERT over positional INSERT OR REPLACE:** The UPSERT explicitly lists 15 columns and their `excluded.*` counterparts in the DO UPDATE SET clause, making column mapping unambiguous and safe for future schema additions.
+
+2. **acknowledged_at hardcoded NULL in UPSERT:** The UPSERT sets `acknowledged_at = NULL` unconditionally in both the INSERT and the ON CONFLICT update clause. This ensures a new event always resets the acknowledged state, matching the pre-existing behavior and test expectations.
+
+3. **PRAGMA placement before DDL:** The FK pragma is placed before all CREATE TABLE statements to ensure the enforcement is active when foreign key relationships are first defined, not just at query time.
+
+## Deviations from Plan
+
+None — plan executed exactly as written.
+
+## Verification Results
+
+- `grep -c "INSERT OR REPLACE INTO updates" pkg/diunwebhook/diunwebhook.go` → `0` (confirmed)
+- `grep -c "PRAGMA foreign_keys = ON" pkg/diunwebhook/diunwebhook.go` → `1` (confirmed)
+- `grep -c "ON CONFLICT(image) DO UPDATE SET" pkg/diunwebhook/diunwebhook.go` → `1` (confirmed)
+- Full test suite: 29 tests pass, 0 failures, coverage 63.6%
+- `TestDismissHandler_ReappearsAfterNewWebhook` — PASS
+- `TestDeleteTagHandler_CascadesAssignment` — PASS
+- `TestUpdateEvent_PreservesTagOnUpsert` — PASS (new regression test)
+
+## Known Stubs
+
+None.
+
+## Self-Check: PASSED
+
+Files exist:
+- FOUND: pkg/diunwebhook/diunwebhook.go (modified)
+- FOUND: pkg/diunwebhook/diunwebhook_test.go (modified, contains TestUpdateEvent_PreservesTagOnUpsert)
+
+Commits exist:
+- FOUND: 7edbaad — fix(01-01): replace INSERT OR REPLACE with UPSERT and enable FK enforcement
+- FOUND: e2d388c — test(01-01): add TestUpdateEvent_PreservesTagOnUpsert regression test