# Milestone v1.4: Memory Leak Prevention

**Status:** SHIPPED 2026-02-10
**Phases:** 19-23
**Total Plans:** 5

## Overview

Fix memory leaks causing session screen freezes after ~10 minutes. Audit and fix cleanup patterns in VU meters, chat window, and session screen components.

## Phases

### Phase 19: Audit and Discovery
**Goal**: Investigate all three areas (VU meters, chat, session screen) and identify actual memory leaks with evidence
**Depends on**: Phase 18 (previous milestone complete)
**Plans**: 1 plan

Plans:
- [x] 19-01: Comprehensive memory leak audit (VU meters, chat, session screen)

**Details:**
Comprehensive audit identified unbounded vuStates growth (HIGH), chat message accumulation (HIGH), and confirmed proper cleanup in base session components. Created prioritized implementation recommendations for Phases 20-22.

### Phase 20: VU Meter Fixes
**Goal**: Fix unbounded vuStates growth by adding removeVuState cleanup function and integrating with track lifecycle
**Depends on**: Phase 19
**Plans**: 1 plan

Plans:
- [x] 20-01: Add removeVuState function and integrate with mixer lifecycle

**Details:**
Added removeVuState callback function to useVuHelpers for targeted state cleanup. Integrated VU state cleanup with mixer lifecycle in useMixerHelper. Uses Set comparison for efficient mixer removal detection and useRef to track previous mixer IDs without triggering re-renders.

### Phase 21: Chat Window Fixes
**Goal**: Fix unbounded message accumulation and add session leave cleanup
**Depends on**: Phase 19
**Plans**: 1 plan

Plans:
- [x] 21-01: Bounded message storage and session leave cleanup (CHAT-02, CHAT-03)

**Details:**
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 dispatch in both leave paths.

### Phase 22: Session Screen Fixes
**Goal**: Fix identified session screen useEffect and polling cleanup issues
**Depends on**: Phase 19
**Plans**: 1 plan

Plans:
- [x] 22-01: Callback cleanup hardening with useRef pattern (SESS-01)

**Details:**
Added registeredCallbacksRef to store callbacks with stable reference. Updated unregisterMessageCallbacks to read from ref instead of state. Callback registration now stores to both state (for reactivity) and ref (for cleanup reliability).

### Phase 23: Verification
**Goal**: Validate session stability after all fixes are applied
**Depends on**: Phase 20, Phase 21, Phase 22
**Plans**: 1 plan

Plans:
- [x] 23-01: Regression tests and manual memory verification UAT

**Details:**
Ran full Playwright test suite (36 pass, 14 fail from pre-existing issues). Created comprehensive UAT checklist covering all memory leak fix areas. User verified 15+ minute session stability with no freezes or performance issues.

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## Milestone Summary

**Key Decisions:**
- Use Set comparison for efficient mixer removal detection
- Track previous mixer IDs with ref to avoid re-render triggers
- MAX_MESSAGES = 500 per channel (sufficient for long sessions while bounding memory)
- useRef alongside useState for callback cleanup stability
- UAT checklist for manual memory profiling (cannot be fully automated)
- 15+ minute stability as primary verification metric

**Issues Resolved:**
- Unbounded vuStates growth causing memory accumulation
- Chat messages accumulating without limit
- Session callback unregistration relying on leave handler only

**Issues Deferred:**
- End-of-track restart requires double-click (Minor) - From v1.0
- Loop functionality not working (Medium) - From v1.0
- Volume control not working in popup mode (Medium) - From v1.0
- WebSocket chat messages only broadcast to musicians (Medium) - From v1.2
- mp3 backend support (Medium) - Frontend allows, backend whitelist doesn't support
- Pre-existing test failures in JKChatMessageList.test.js (Low) - Missing activeSession state

**Technical Debt Incurred:**
- None - minimal changes focused only on leak fixes

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*For current project status, see .planning/ROADMAP.md (or next milestone's roadmap)*
