diff --git a/.planning/STATE.md b/.planning/STATE.md
index a1145a4..ea25abf 100644
--- a/.planning/STATE.md
+++ b/.planning/STATE.md
@@ -19,9 +19,9 @@ Progress: [████████░░] 85%
 ## Performance Metrics
 
 **Velocity:**
-- Total plans completed: 11
+- Total plans completed: 12
 - Average duration: 3.6 min
-- Total execution time: 44 min
+- Total execution time: 46 min
 
 **By Phase:**
 
@@ -30,10 +30,10 @@ Progress: [████████░░] 85%
 | 01-foundation | 2 | 7 min | 3.5 min |
 | 02-core-crud | 4 | 15 min | 3.75 min |
 | 03-images | 4 | 14 min | 3.5 min |
-| 04-tags | 1 | 8 min | 8 min |
+| 04-tags | 2 | 10 min | 5 min |
 
 **Recent Trend:**
-- Last 5 plans: 03-01 (4 min), 03-02 (2 min), 03-03 (2 min), 03-04 (8 min), 04-02 (8 min)
+- Last 5 plans: 03-02 (2 min), 03-03 (2 min), 03-04 (8 min), 04-02 (8 min), 04-01 (2 min)
 - Trend: Stable
 
 *Updated after each plan completion*
@@ -74,6 +74,9 @@ Recent decisions affecting current work:
 - Fetch/invalidateAll pattern for pin toggle actions (04-02)
 - Due date stored as ISO string from HTML5 date input (04-02)
 - Pinned section uses uppercase label for visual distinction (04-02)
+- Tags stored with original case but matched case-insensitively (04-01)
+- Entry tags replaced atomically via delete-then-insert (04-01)
+- lower() helper for case-insensitive SQL queries (04-01)
 
 ### Pending Todos
 
@@ -86,9 +89,9 @@ None yet.
 ## Session Continuity
 
 Last session: 2026-01-31
-Stopped at: Completed 04-02-PLAN.md
+Stopped at: Completed 04-01-PLAN.md (2/3 plans complete in phase 4)
 Resume file: None
 
 ---
 *State initialized: 2026-01-29*
-*Last updated: 2026-01-31 after 04-02 completion*
+*Last updated: 2026-01-31 after 04-01 completion*
diff --git a/.planning/phases/04-tags/04-01-SUMMARY.md b/.planning/phases/04-tags/04-01-SUMMARY.md
new file mode 100644
index 0000000..91dae7d
--- /dev/null
+++ b/.planning/phases/04-tags/04-01-SUMMARY.md
@@ -0,0 +1,99 @@
+---
+phase: 04-tags
+plan: 01
+subsystem: database
+tags: [drizzle, sqlite, many-to-many, tags, junction-table]
+
+# Dependency graph
+requires:
+  - phase: 01-foundation
+    provides: entries and images schema, repository pattern
+provides:
+  - tags table with case-insensitive unique constraint
+  - entry_tags junction table for many-to-many relationships
+  - tagRepository with findOrCreate, getAll, getById, getByEntryId, updateEntryTags
+  - lower() SQL helper function for case-insensitive queries
+affects: [04-02-tag-ui, 04-03-tag-filter, future-search]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns:
+    - "Case-insensitive unique index using lower() SQL helper"
+    - "Junction table with composite primary key"
+    - "Atomic tag replacement via delete-then-insert"
+
+key-files:
+  created: []
+  modified:
+    - src/lib/server/db/schema.ts
+    - src/lib/server/db/repository.ts
+
+key-decisions:
+  - "Tags stored with original case but matched case-insensitively"
+  - "Entry tags replaced atomically (full replace, not incremental)"
+  - "Orphaned tags remain in database for autocomplete history"
+
+patterns-established:
+  - "lower() helper: Use for case-insensitive SQL comparisons"
+  - "Junction table: Composite PK with cascade deletes on both FKs"
+
+# Metrics
+duration: 2min
+completed: 2026-01-31
+---
+
+# Phase 4 Plan 1: Tag Schema & Repository Summary
+
+**Tags and entry_tags tables with case-insensitive uniqueness, cascade deletes, and tagRepository with atomic entry tag updates**
+
+## Performance
+
+- **Duration:** 2 min
+- **Started:** 2026-01-31T12:02:29Z
+- **Completed:** 2026-01-31T12:04:34Z
+- **Tasks:** 2
+- **Files modified:** 2
+
+## Accomplishments
+- Tags table with case-insensitive unique index on name using lower() helper
+- Entry_tags junction table with composite primary key and cascade deletes
+- TagRepository with findOrCreate, getAll, getById, getByEntryId, updateEntryTags methods
+- Database schema synced via drizzle-kit push
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Add tags schema with case-insensitive unique index** - `7dc63e6` (feat)
+2. **Task 2: Create tagRepository with tag operations** - `378d928` (feat)
+
+## Files Created/Modified
+- `src/lib/server/db/schema.ts` - Added tags table, entry_tags junction table, lower() helper, type exports
+- `src/lib/server/db/repository.ts` - Added TagRepository interface and SQLiteTagRepository implementation
+
+## Decisions Made
+- Store tags with original user-provided casing but match case-insensitively
+- Replace entry tags atomically: delete all existing, then insert new set
+- Keep orphaned tags in database (useful for autocomplete suggestions)
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+
+None
+
+## User Setup Required
+
+None - no external service configuration required.
+
+## Next Phase Readiness
+- Tag schema and repository ready for UI integration
+- Ready for plan 04-02 (tag input UI with autocomplete)
+- Ready for plan 04-03 (filter by tag)
+
+---
+*Phase: 04-tags*
+*Completed: 2026-01-31*