docs(21-01): complete Chat State Cleanup plan

Tasks completed: 2/2
- Add MAX_MESSAGES limit to sessionChatSlice.js
- Add clearAllMessages action and dispatch on session leave

SUMMARY: .planning/phases/21-chat-window-fixes/21-01-SUMMARY.md

.planning/STATE.md

@@ -5,16 +5,16 @@
 See: .planning/PROJECT.md (updated 2026-02-08)
 
 **Core value:** Fix memory leaks to ensure stable session experience without freezes
-**Current focus:** v1.4 Memory Leak Prevention - Phase 20 VU Meter Fixes
+**Current focus:** v1.4 Memory Leak Prevention - Phase 21 Chat Window Fixes
 
 ## Current Position
 
-Phase: 20 of 23 (VU Meter Fixes)
+Phase: 21 of 23 (Chat Window Fixes)
 Plan: 01 of 01 - Complete
 Status: Phase complete
-Last activity: 2026-02-08 — Completed 20-01-PLAN.md (VU State Cleanup)
+Last activity: 2026-02-08 - Completed 21-01-PLAN.md (Chat State Cleanup)
 
-Progress (v1.4): [████████░░░░░░░░░░░░] 40%
+Progress (v1.4): [██████████░░░░░░░░░░] 50%
 
 ## Performance Metrics
 
@@ -45,7 +45,7 @@ Progress (v1.4): [████████░░░░░░░░░░░░]
 **v1.4 Memory Leak Prevention (In Progress):**
 - Phases: 5 (phases 19-23)
 - Requirements: 11
-- Plans completed: 2 (19-01, 20-01)
+- Plans completed: 3 (19-01, 20-01, 21-01)
 
 ## Accumulated Context
 
@@ -63,6 +63,9 @@ Decisions are logged in PROJECT.md Key Decisions table.
 | 2026-02-08 | 20-01 | Use Set comparison for mixer removal detection | Efficient Set.has() lookup for removed mixers |
 | 2026-02-08 | 20-01 | Track previous mixer IDs with ref | Avoids re-render triggers from tracking state |
 | 2026-02-08 | 20-01 | Guard cleanup with isReadyRedux check | Prevents false positives during initial mount |
+| 2026-02-08 | 21-01 | MAX_MESSAGES = 500 per channel | Sufficient for long sessions while bounding memory |
+| 2026-02-08 | 21-01 | Preserve lastReadAt across sessions | Keeps unread badge accurate for UX continuity |
+| 2026-02-08 | 21-01 | Clear chat before session state | Ensures proper cleanup order |
 
 ### Deferred Issues
 
@@ -84,11 +87,10 @@ Decisions are logged in PROJECT.md Key Decisions table.
 ## Session Continuity
 
 Last session: 2026-02-08
-Stopped at: Completed 20-01-PLAN.md (VU State Cleanup)
+Stopped at: Completed 21-01-PLAN.md (Chat State Cleanup)
 Resume file: None
 
 **Next steps:**
-1. Run `/gsd:plan-phase 21` to plan Chat Fixes phase
-2. Implement CHAT-01 (bounded chat message history)
-3. Continue to Phase 22 for Session Screen Cleanup
-4. Verify memory leak fixes with extended session testing
+1. Run `/gsd:plan-phase 22` to plan Session Screen Cleanup phase
+2. Continue memory leak prevention work
+3. Phase 23 will verify all memory leak fixes with extended session testing

.planning/phases/21-chat-window-fixes/21-01-SUMMARY.md

@@ -0,0 +1,99 @@
+---
+phase: 21-chat-window-fixes
+plan: 01
+subsystem: state-management
+tags: [redux, memory-leak, chat, cleanup]
+
+# Dependency graph
+requires:
+  - phase: 19-audit-and-discovery
+    provides: "CHAT-02 and CHAT-03 memory leak identification"
+provides:
+  - "Bounded chat message storage (MAX_MESSAGES = 500 per channel)"
+  - "Chat state cleanup on session leave (clearAllMessages action)"
+  - "Memory leak prevention for chat feature"
+affects:
+  - "22-session-screen-cleanup"
+  - "23-verification-and-testing"
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns:
+    - "Bounded Redux array storage with slice(-MAX_MESSAGES)"
+    - "State cleanup dispatched before session state clear"
+
+key-files:
+  created: []
+  modified:
+    - "jam-ui/src/store/features/sessionChatSlice.js"
+    - "jam-ui/src/components/client/JKSessionScreen.js"
+
+key-decisions:
+  - "MAX_MESSAGES = 500 per channel (sufficient for long sessions)"
+  - "Clear chat state before session state for proper cleanup order"
+  - "Preserve lastReadAt across sessions for UX continuity"
+
+patterns-established:
+  - "Bounded array pattern: slice(-MAX) after push/merge to cap growth"
+  - "State cleanup pattern: dispatch cleanup before parent state clear"
+
+# Metrics
+duration: 2min
+completed: 2026-02-08
+---
+
+# Phase 21 Plan 01: Chat State Cleanup Summary
+
+**Bounded chat message storage (500 per channel) with clearAllMessages action to prevent unbounded memory growth**
+
+## Performance
+
+- **Duration:** 2 min
+- **Started:** 2026-02-08T15:20:26Z
+- **Completed:** 2026-02-08T15:22:39Z
+- **Tasks:** 2
+- **Files modified:** 2
+
+## Accomplishments
+- Added MAX_MESSAGES = 500 constant to bound chat message arrays
+- Applied slice(-MAX_MESSAGES) in all 3 message-adding reducers
+- Created clearAllMessages action for session leave cleanup
+- Integrated clearAllMessages dispatch in both leave paths
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Add MAX_MESSAGES limit to sessionChatSlice.js** - `f1189af67` (feat)
+2. **Task 2: Add clearAllMessages action and dispatch on session leave** - `5407f1959` (feat)
+
+## Files Created/Modified
+- `jam-ui/src/store/features/sessionChatSlice.js` - Added MAX_MESSAGES constant, slice bounds in 3 reducers, clearAllMessages action
+- `jam-ui/src/components/client/JKSessionScreen.js` - Import and dispatch clearAllMessages in handleLeaveSubmit and cleanup useEffect
+
+## Decisions Made
+- **MAX_MESSAGES = 500**: Sufficient for long sessions while bounding memory. Average chat rate doesn't approach this in normal use.
+- **Preserve lastReadAt**: Keeps unread badge accurate across sessions for UX continuity.
+- **Clear before session state**: clearAllMessages dispatched before clearSession to ensure proper cleanup order.
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+
+None - pre-existing Prettier formatting errors in both files are not related to this change and were not addressed (out of scope).
+
+## User Setup Required
+
+None - no external service configuration required.
+
+## Next Phase Readiness
+- Chat memory leak fixes complete (CHAT-02 and CHAT-03 addressed)
+- CHAT-01 was verified OK in Phase 19 audit
+- Ready for Phase 22 (Session Screen Cleanup) or Phase 23 (Verification)
+
+---
+*Phase: 21-chat-window-fixes*
+*Completed: 2026-02-08*