docs(quick-10): complete fix duplicate album merging bug plan

- Add 10-SUMMARY.md with full execution details
- Update STATE.md with quick task 10 entry and session info

.planning/STATE.md

@@ -57,17 +57,18 @@ Decisions from v1.0 are archived in PROJECT.md Key Decisions table. Key patterns
 | 007 | Pin default playlist to top | 2026-03-01 | e6378e1 |
 | 008 | Duplicate tracks dialog | 2026-03-01 | 917a79a |
 | 009 | Fix queue panel scroll bar not following mouse | 2026-03-05 | ebde5e5 |
+| 010 | Fix duplicate album merging bug (composite unique constraint) | 2026-03-05 | d43ba7b |
 
 ## Session Continuity
 
 ### Last Session
 
 **Date:** 2026-03-05
-**What happened:** Quick task 9 — fixed queue panel scrollbar not following mouse on large queues by setting fixed height on track items.
+**What happened:** Quick task 10 — fixed album merging bug where albums with same name but different artists were merged into a single entry. Added composite unique constraint on (name, album_artist_credit_id), migration 5, and fixed entity cache.
-**Where we stopped:** Completed quick-9 plan. Needs human verification of scrollbar behavior.
+**Where we stopped:** Completed quick-10 plan. User should trigger full library rescan to split previously merged albums.
-**Next action:** Verify scrollbar tracks mouse 1:1 on 20k+ queue, then `/gsd-new-milestone`
+**Next action:** Rescan library to split merged albums, then `/gsd-new-milestone`
 
 ---
 *State initialized: 2026-02-27*
-Last activity: 2026-03-05 - Quick task 9: fix queue panel scroll bar
+Last activity: 2026-03-05 - Quick task 10: fix duplicate album merging bug
 *Last updated: 2026-03-05*

.planning/quick/10-diagnose-duplicate-album-merging-bug-alb/10-SUMMARY.md

@@ -0,0 +1,97 @@
+---
+phase: quick-10
+plan: 10
+subsystem: database, library
+tags: [bugfix, schema-migration, sqlite, entity-cache]
+dependency_graph:
+  requires: []
+  provides: [composite-unique-release-groups, migration-5]
+  affects: [release_groups, library-scan, cover-grid]
+tech_stack:
+  added: []
+  patterns: [composite-unique-constraint, table-rebuild-migration, composite-cache-key]
+key_files:
+  created: []
+  modified:
+    - backend/database/sql/schemas/release_groups.sql
+    - backend/database/sql/queries/release_groups.sql
+    - backend/database/sql/sqlcgen/release_groups.sql.go
+    - backend/database/database.go
+    - backend/library/library.go
+    - backend/library/scan_test.go
+decisions:
+  - "Rename GetReleaseGroupByName to GetReleaseGroupByNameAndArtist (no callers outside generated code)"
+  - "Use null byte separator in composite cache key for safety"
+  - "Drop and recreate track_metadata VIEW during migration to avoid SQLite VIEW dependency error"
+metrics:
+  duration: 5m25s
+  completed: "2026-03-05"
+  tasks_completed: 2
+  tasks_total: 2
+---
+
+# Quick Task 10: Fix Duplicate Album Merging Bug
+
+Composite unique constraint on (name, album_artist_credit_id) for release_groups, with migration 5 to rebuild existing tables and entity cache fix to key by album+artist.
+
+## Task Summary
+
+| # | Task | Commit | Key Changes |
+|---|------|--------|-------------|
+| 1 | Fix schema, queries, and regenerate sqlc | 999ab96 | UNIQUE(name, album_artist_credit_id) in schema; ON CONFLICT updated; GetReleaseGroupByNameAndArtist |
+| 2 | Add migration 5 and fix entity cache | d43ba7b | Migration 5 rebuilds table; cache keys by album+artistID; VIEW drop/recreate |
+
+## What Changed
+
+### Schema (`release_groups.sql`)
+- Removed `UNIQUE` from `name TEXT NOT NULL UNIQUE`
+- Added table-level `UNIQUE(name, album_artist_credit_id)` — SQLite treats NULL as unique, so albums without an artist won't collide
+
+### Queries (`release_groups.sql`)
+- `UpsertReleaseGroup`: `ON CONFLICT(name)` → `ON CONFLICT(name, album_artist_credit_id)`
+- `GetReleaseGroupByName` → `GetReleaseGroupByNameAndArtist` with two params (name + album_artist_credit_id)
+
+### Migration 5 (`database.go`)
+- Disables FK checks temporarily
+- Drops `track_metadata` VIEW (depends on release_groups)
+- Creates `release_groups_new` with composite unique constraint
+- Copies data, drops old, renames new
+- Recreates both indexes and the `track_metadata` VIEW
+- Re-enables FK checks, bumps user_version to 5
+
+### Entity Cache (`library.go`)
+- Cache key changed from `tags.Album` to `fmt.Sprintf("%s\x00%d", tags.Album, artistID)` where artistID is -1 when no album artist credit exists
+- All 3 cache access points updated (lookup, cover art update, store after upsert)
+
+## Deviations from Plan
+
+### Auto-fixed Issues
+
+**1. [Rule 1 - Bug] track_metadata VIEW blocking table rename**
+- **Found during:** Task 2
+- **Issue:** SQLite refuses to rename `release_groups_new` to `release_groups` when the `track_metadata` VIEW references the old table
+- **Fix:** Drop the VIEW before table rebuild, recreate it after rename (VIEW definition matches embedded schema exactly)
+- **Files modified:** backend/database/database.go
+- **Commit:** d43ba7b
+
+**2. [Rule 1 - Bug] Tests using old cache key format**
+- **Found during:** Task 2
+- **Issue:** `TestResolveReleaseGroup` and `TestResolveReleaseGroup_CacheHit` use bare album name as cache key
+- **Fix:** Updated test assertions to use composite cache key format (`albumName\x00artistCreditID`)
+- **Files modified:** backend/library/scan_test.go
+- **Commit:** d43ba7b
+
+## Verification
+
+- `go build ./...` — passes
+- `go test ./...` — all 14 test packages pass
+- `go vet ./...` — no issues
+- Schema has `UNIQUE(name, album_artist_credit_id)` ✓
+- UpsertReleaseGroup uses `ON CONFLICT(name, album_artist_credit_id)` ✓
+- Migration 5 exists and rebuilds table ✓
+- Entity cache key includes artist credit ID ✓
+
+## Notes
+
+- **Existing databases**: Migration 5 changes the constraint but does NOT split already-merged albums. Users must trigger a full library rescan after upgrading.
+- **NULL handling**: SQLite's UNIQUE treats each NULL as distinct, so albums without `album_artist_credit_id` will each get their own row — this is desired behavior.