diff --git a/.planning/STATE.md b/.planning/STATE.md
index ac236b3..1ab5150 100644
--- a/.planning/STATE.md
+++ b/.planning/STATE.md
@@ -10,18 +10,18 @@ See: .planning/PROJECT.md (updated 2026-02-04)
 ## Current Position
 
 Phase: 21 of 21 (Polish & Integration) - In progress
-Plan: 4 of 6 in current phase
-Status: Completed 21-04 (Subscription Error Handling)
-Last activity: 2026-02-05 - Completed 21-04-PLAN.md (subscription error toasts)
+Plan: 5 of 6 in current phase
+Status: Completed 21-05 (Code Splitting & Data-Fetching Performance)
+Last activity: 2026-02-05 - Completed 21-05-PLAN.md (route code splitting + PlanTasksFetcher fix)
 
 Progress: █████████░ 99%
 
 ## Performance Metrics
 
 **Velocity:**
-- Total plans completed: 73
+- Total plans completed: 74
 - Average duration: 3 min
-- Total execution time: 206 min
+- Total execution time: 209 min
 
 **By Phase (v1.0):**
 
@@ -247,6 +247,8 @@ Recent decisions affecting current work:
 - 21-04: duration: Infinity keeps error toast visible until user dismisses — persistent connection feedback
 - 21-04: No reconnection logic — tRPC SSE httpSubscriptionLink handles reconnection via EventSource retry
 - 21-04: SpawnArchitectDropdown already covered by 21-01 — verification task was no-op
+- 21-05: autoCodeSplitting: true on TanStackRouterVite plugin — automatic route splitting without manual .lazy.tsx files
+- 21-05: PlanTasksFetcher onTasks moved to useEffect to prevent setState-during-render loops
 
 ### Pending Todos
 
@@ -269,5 +271,5 @@ None.
 ## Session Continuity
 
 Last session: 2026-02-05
-Stopped at: Completed 21-04 (Subscription Error Handling)
+Stopped at: Completed 21-05 (Code Splitting & Data-Fetching Performance)
 Resume file: None
diff --git a/.planning/phases/21-polish-integration/21-05-SUMMARY.md b/.planning/phases/21-polish-integration/21-05-SUMMARY.md
new file mode 100644
index 0000000..2846750
--- /dev/null
+++ b/.planning/phases/21-polish-integration/21-05-SUMMARY.md
@@ -0,0 +1,92 @@
+---
+phase: 21-polish-integration
+plan: 05
+subsystem: ui
+tags: [vite, tanstack-router, code-splitting, performance, react]
+
+# Dependency graph
+requires:
+  - phase: 21-01
+    provides: ErrorBoundary, toast infrastructure
+  - phase: 21-02
+    provides: Skeleton loading states
+  - phase: 21-03
+    provides: Navigation links, mobile responsive
+provides:
+  - Route-based code splitting via TanStack Router autoCodeSplitting
+  - PlanTasksFetcher render loop fix (setState-during-render eliminated)
+affects: [21-polish-integration]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns: [autoCodeSplitting for route-level lazy loading]
+
+key-files:
+  modified:
+    - packages/web/vite.config.ts
+    - packages/web/src/routes/initiatives/$id.tsx
+
+key-decisions:
+  - "autoCodeSplitting: true on TanStackRouterVite plugin — automatic route splitting without manual .lazy.tsx files"
+  - "PlanTasksFetcher onTasks moved to useEffect to prevent setState-during-render loops"
+
+patterns-established:
+  - "autoCodeSplitting handles route chunk boundaries automatically — no manual lazy route files needed"
+
+# Metrics
+duration: 3min
+completed: 2026-02-05
+---
+
+# Phase 21 Plan 05: Code Splitting & Data-Fetching Performance Summary
+
+**Route-based code splitting and PlanTasksFetcher render loop optimization**
+
+## Performance
+
+- **Duration:** 3 min
+- **Started:** 2026-02-05
+- **Completed:** 2026-02-05
+- **Tasks:** 2
+- **Files modified:** 2
+
+## Accomplishments
+- Enabled `autoCodeSplitting: true` on TanStackRouterVite plugin, splitting monolithic 582 KB bundle into route-level chunks
+- Main vendor chunk reduced to 454 KB (below 500 KB warning threshold)
+- Route chunks: initiative detail (~13 KB), inbox (~13 KB), dashboard (~65 KB), dialog (~38 KB)
+- Fixed PlanTasksFetcher calling onTasks during render, moved to useEffect with proper dependency array
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Add route-based code splitting via TanStack Router lazy routes** - `1530d7a` (feat)
+2. **Task 2: Optimize PlanTasksFetcher render loop in initiative detail** - `c66d7ec` (fix)
+
+## Files Created/Modified
+- `packages/web/vite.config.ts` - Added `autoCodeSplitting: true` to TanStackRouterVite plugin options
+- `packages/web/src/routes/initiatives/$id.tsx` - Moved onTasks callback from render body to useEffect in PlanTasksFetcher
+
+## Decisions Made
+- Used `autoCodeSplitting: true` instead of manual `.lazy.tsx` file convention — the plugin handles splitting automatically
+- PlanTasksFetcher data flow changed from synchronous render-time callback to useEffect-based callback
+
+## Deviations from Plan
+
+None - plan executed exactly as written. The `autoCodeSplitting` option was available in the installed version of @tanstack/router-plugin (^1.158.0), so manual .lazy.tsx splitting was not needed.
+
+## Issues Encountered
+None
+
+## User Setup Required
+None - no external service configuration required.
+
+## Next Phase Readiness
+- Plan 21-05 complete, ready for 21-06
+- Bundle split into multiple route-level chunks
+- No setState-during-render warnings in PlanTasksFetcher
+
+---
+*Phase: 21-polish-integration*
+*Completed: 2026-02-05*