docs(20): complete plan 20-01 SSE streaming summary and state update

.planning/STATE.md

@@ -9,19 +9,19 @@ See: .planning/PROJECT.md (updated 2026-02-04)
 
 ## Current Position
 
-Phase: 19 of 21 (Agent Inbox) - COMPLETE
-Plan: 4 of 4 in current phase
-Status: Phase 19 complete
-Last activity: 2026-02-04 - Completed 19-04-PLAN.md (Inbox Page Assembly)
+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)
 
-Progress: █████████░ 98%
+Progress: █████████░ 99%
 
 ## Performance Metrics
 
 **Velocity:**
-- Total plans completed: 70
+- Total plans completed: 71
 - Average duration: 3 min
-- Total execution time: 197 min
+- Total execution time: 201 min
 
 **By Phase (v1.0):**
 
@@ -225,6 +225,10 @@ Recent decisions affecting current work:
 - 19-04: Detail panel inline in page file (not a separate component) — page-specific layout
 - 19-04: useUtils() for query invalidation on mutation success (same pattern as initiative detail)
 - 19-04: Serialize agent/message data to string dates for InboxList props (wire format consistency)
+- 20-01: Queue + deferred promise pattern for bridging push (EventBus) to pull (async generator)
+- 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)
 
 ### Pending Todos
 
@@ -247,5 +251,5 @@ None.
 ## Session Continuity
 
 Last session: 2026-02-04
-Stopped at: Completed 19-04 (Inbox Page Assembly) — Phase 19 complete
+Stopped at: Completed 20-01 (SSE Streaming & Subscription Procedures)
 Resume file: None