---
phase: 27-backing-track-sync
verified: 2026-02-26T11:53:24Z
status: passed
score: 2/2 must-haves verified
---

# Phase 27: Backing Track Sync Verification Report

**Phase Goal:** Backing Track appears in session screen when opened
**Verified:** 2026-02-26T11:53:24Z
**Status:** passed
**Re-verification:** No - initial verification

## Goal Achievement

### Observable Truths

| # | Truth | Status | Evidence |
|---|-------|--------|----------|
| 1 | Opening a backing track file shows the track in session screen (not just popup) | VERIFIED | `handleBackingTrackSelected` at line 1137 calls `await openBackingTrack(result.file)` which triggers `syncTracksToServer` in useMediaActions hook |
| 2 | No "state update on unmounted component" warnings when closing backing track quickly | VERIFIED | JKSessionBackingTrackPlayer.js useEffect at line 90 has `let ignore = false` declaration and cleanup function at line 155-157 sets `ignore = true` |

**Score:** 2/2 truths verified

### Required Artifacts

| Artifact | Expected | Status | Details |
|----------|----------|--------|---------|
| `jam-ui/src/components/client/JKSessionScreen.js` | handleBackingTrackSelected using openBackingTrack action | VERIFIED | Line 1144: `await openBackingTrack(result.file);` - uses action from useMediaActions (imported line 18, destructured line 153) |
| `jam-ui/src/components/client/JKSessionBackingTrackPlayer.js` | Duration fetch useEffect with cleanup | VERIFIED | Lines 90-158: useEffect with `let ignore = false` (line 91), async checks, and cleanup `return () => { ignore = true; }` (lines 155-157) |

### Key Link Verification

| From | To | Via | Status | Details |
|------|-----|-----|--------|---------|
| JKSessionScreen.js handleBackingTrackSelected | useMediaActions openBackingTrack | async await call | VERIFIED | Line 1144: `await openBackingTrack(result.file)` - openBackingTrack destructured from useMediaActions() at line 153 |
| JKSessionBackingTrackPlayer.js useEffect | cleanup function | return statement | VERIFIED | Lines 155-157: `return () => { ignore = true; };` |
| openBackingTrack hook function | syncTracksToServer | dispatch call | VERIFIED | useMediaActions.js line 60: `dispatch(syncTracksToServer(sessionId, jamClient))` |

### Requirements Coverage

| Requirement | Status | Blocking Issue |
|-------------|--------|----------------|
| BT-01: Use openBackingTrack() action to enable track sync to session screen | SATISFIED | None |
| BT-02: Add ignore flag to duration fetch useEffect | SATISFIED | None |

### Anti-Patterns Found

| File | Line | Pattern | Severity | Impact |
|------|------|---------|----------|--------|
| JKSessionScreen.js | 1158 | TODO comment about native window | Info | Pre-existing, not related to Phase 27 changes |

Note: JKSessionBackingTrackPlayer.js has no TODO/FIXME patterns.

### Human Verification Required

#### 1. Visual Verification: Backing Track in Session Screen
**Test:** Open a backing track file in session
**Expected:** Backing track appears in the session screen track list (not just in popup)
**Why human:** Requires running app with native client to verify visual rendering

#### 2. Console Warning Check
**Test:** Open backing track popup, then close it immediately (within 1-2 seconds)
**Expected:** No React warning "Can't perform a React state update on an unmounted component"
**Why human:** Requires running app and monitoring browser console during rapid open/close

### Summary

All must-haves have been verified in the codebase:

1. **Backing track sync:** The `handleBackingTrackSelected` function now uses `openBackingTrack(result.file)` action from useMediaActions hook. This action:
   - Calls `openBackingTrackThunk` which invokes `jamClient.SessionOpenBackingTrackFile`
   - Sets `mediaSummary.backingTrackOpen = true`
   - Calls `syncTracksToServer(sessionId, jamClient)` to sync track to session screen

2. **Async cleanup:** The duration fetch useEffect in JKSessionBackingTrackPlayer.js implements the ignore flag pattern:
   - `let ignore = false` at useEffect start (line 91)
   - `if (ignore) return` checks before async operation (line 104) and after (line 119)
   - `if (!ignore)` guard in catch block (line 143)
   - Cleanup function `return () => { ignore = true; }` (lines 155-157)

The direct `jamClient.SessionOpenBackingTrackFile` call has been removed from handleBackingTrackSelected (grep confirms no matches).

---

*Verified: 2026-02-26T11:53:24Z*
*Verifier: Claude (gsd-verifier)*
