docs(20-02): create summary and update state for frontend subscriptions

Phase 20 (Real-Time Subscriptions) is now complete. Both plans delivered:
- 20-01: SSE backend with subscription procedures
- 20-02: Frontend splitLink + subscription hooks on all 3 UI pages

.planning/STATE.md

@@ -9,19 +9,19 @@ See: .planning/PROJECT.md (updated 2026-02-04)
 
 ## Current Position
 
-Phase: 20 of 21 (Real-Time Subscriptions) - IN PROGRESS
-Plan: 1 of 2 in current phase
-Status: Completed 20-01 (SSE Streaming & Subscription Procedures)
-Last activity: 2026-02-04 - Completed 20-01-PLAN.md (SSE backend)
+Phase: 20 of 21 (Real-Time Subscriptions) - COMPLETE
+Plan: 2 of 2 in current phase (all complete)
+Status: Completed 20-02 (Frontend SSE Subscription Hooks)
+Last activity: 2026-02-04 - Completed 20-02-PLAN.md (frontend subscriptions)
 
 Progress: █████████░ 99%
 
 ## Performance Metrics
 
 **Velocity:**
-- Total plans completed: 71
+- Total plans completed: 72
 - Average duration: 3 min
-- Total execution time: 201 min
+- Total execution time: 204 min
 
 **By Phase (v1.0):**
 
@@ -229,6 +229,10 @@ Recent decisions affecting current work:
 - 20-01: tracked() wrapper on each event for client-side reconnection via lastEventId
 - 20-01: Fallback AbortSignal (new AbortController().signal) when opts.signal is undefined
 - 20-01: Vite proxy works for SSE without changes (http-proxy streams chunked responses by default)
+- 20-02: httpSubscriptionLink (stable export) over unstable_ prefix — both available in @trpc/client v11
+- 20-02: Subscription-driven invalidation (not local state) — simplest approach, reuses existing React Query cache
+- 20-02: Silent onError callbacks — pages degrade to manual refresh when backend is not running
+- 20-02: No new packages needed — splitLink and httpSubscriptionLink ship with @trpc/client v11
 
 ### Pending Todos
 
@@ -251,5 +255,5 @@ None.
 ## Session Continuity
 
 Last session: 2026-02-04
-Stopped at: Completed 20-01 (SSE Streaming & Subscription Procedures)
+Stopped at: Completed 20-02 (Frontend SSE Subscription Hooks) — Phase 20 complete
 Resume file: None