music_library/backlog/tasks/ml-188 - Fix-form-edit-background-update-race-in-Show-LiveViews.md

id, title, status, assignee, created_date, labels, dependencies, documentation, modified_files, priority, ordinal

id	title	status	assignee	created_date	labels	dependencies	documentation	modified_files	priority	ordinal
ML-188	Fix form edit + background update race in Show LiveViews	To Do		2026-05-19 08:42	audit bug race-condition liveview pubsub		audits/phase3-concurrent-state-safety/doc-26 - Audit-Report-Concurrent-State-Change-Safety-Phase-3.md	lib/music_library_web/live/collection_live/show.ex lib/music_library_web/live/wishlist_live/show.ex	medium	23000

Description

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.

Acceptance Criteria

• #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