ML-169.10: add optimistic delete UI fix task

backlog/tasks/ml-169.10 - Fix-Missing-optimistic-UI-for-delete-operations.md

@@ -0,0 +1,69 @@
+---
+id: ML-169.10
+title: "Fix: Missing optimistic UI for delete operations"
+status: To Do
+assignee: []
+created_date: "2026-05-19 11:48"
+labels:
+  - perf
+  - fix
+  - ux
+dependencies: []
+references:
+  - >-
+    backlog/documents/doc-27 -
+    Phase-4-Performance-Audit-Low-Hanging-Fruit-Findings.md
+modified_files:
+  - lib/music_library_web/live_helpers/index_actions.ex
+  - lib/music_library_web/live/collection_live/show.ex
+  - lib/music_library_web/live/scrobbled_tracks_live/index.ex
+parent_task_id: ML-169
+priority: medium
+ordinal: 31000
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+
+Add optimistic UI for delete operations so the UI removes items immediately without waiting for the database transaction.
+
+## Problem
+
+All delete operations wait for the database transaction to complete before updating the UI. `stream_delete` is already used in some places, but the pattern is inconsistent. CollectionLive.Show deletes don't use `stream_delete` at all (they navigate away).
+
+## Files
+
+- `lib/music_library_web/live_helpers/index_actions.ex:94-98` — `handle_delete`
+- `lib/music_library_web/live/collection_live/show.ex:381-385` — `handle_event("delete")`
+- `lib/music_library_web/live/scrobbled_tracks_live/index.ex:305-310` — `handle_event("delete")`
+
+## Impact
+
+Adds unnecessary latency to delete operations that could feel instant. While delete failures are rare, the benefit of snappy UI is worth the minimal risk.
+
+## Fix
+
+Use `stream_delete` immediately, then perform the DB operation async. If DB fails, re-insert the item and show error toast.
+
+```elixir
+def handle_delete(socket, id) do
+  record = Records.get_record!(id)
+  socket = stream_delete(socket, :records, record)
+  Task.start(fn -> Records.delete_record(record) end)
+  {:noreply, socket}
+end
+```
+
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+
+<!-- AC:BEGIN -->
+
+- [ ] #1 Delete operations remove items from UI immediately (no DB wait)
+- [ ] #2 Database delete still executes successfully in background
+- [ ] #3 If DB delete fails, item is re-inserted into stream and error toast shown
+- [ ] #4 Existing delete confirmation modal still works correctly
+- [ ] #5 No orphaned UI state after failed delete
+<!-- AC:END -->