ML-188: add form edit + background update race fix task

From audit doc-26 (Phase 3), Recommendation #1.
2026-05-19 09:46:11 +01:00
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+---
+id: ML-188
+title: Fix form edit + background update race in Show LiveViews
+status: To Do
+assignee: []
+created_date: "2026-05-19 08:42"
+labels:
+  - audit
+  - bug
+  - race-condition
+  - liveview
+  - pubsub
+dependencies: []
+documentation:
+  - >-
+    audits/phase3-concurrent-state-safety/doc-26 -
+    Audit-Report-Concurrent-State-Change-Safety-Phase-3.md
+modified_files:
+  - lib/music_library_web/live/collection_live/show.ex
+  - lib/music_library_web/live/wishlist_live/show.ex
+priority: medium
+ordinal: 23000
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+
+When a user is editing a record in a modal (`live_action == :edit`) and a background worker (e.g., PopulateGenres, RefreshCover) broadcasts `{:update, record}`, the Show LiveView's `handle_info` overwrites `@record` on the socket. The next save by the user can silently revert the worker's changes because the form data was based on the stale `@record`.
+
+**Race flow:**
+
+1. User opens edit modal with record v1
+2. Background worker updates DB to v2, broadcasts `{:update, v2}`
+3. `handle_info` assigns v2 → RecordForm gets v2 via `update/2`
+4. User saves → stale form params overwrite worker's v2 changes in DB
+
+**Fix:** Add a `live_action` guard to `handle_info({:update, record})` in both CollectionLive.Show and WishlistLive.Show. When `live_action == :edit`, skip assigning the updated record and show a warning toast that the record was updated in the background. The fresh record will be loaded on the next `handle_params` when the user navigates away from edit mode.
+
+**Source:** Audit doc-26 (Phase 3), Recommendation #1.
+
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+
+<!-- AC:BEGIN -->
+
+- [ ] #1 handle_info({:update, record}) skips assign(:record, ...) when live_action == :edit in CollectionLive.Show
+- [ ] #2 handle_info({:update, record}) skips assign(:record, ...) when live_action == :edit in WishlistLive.Show
+- [ ] #3 Warning toast shown to user when background update occurs during edit
+- [ ] #4 handle_info({:update, record}) still works normally when live_action == :show
+- [ ] #5 When user navigates away from edit, handle_params re-fetches fresh record with worker changes
+<!-- AC:END -->