ML-169.5: add display toggle performance fix task

backlog/tasks/ml-169.5 - Fix-Display-toggle-grid-list-triggers-full-DB-reload.md

@@ -0,0 +1,58 @@
+---
+id: ML-169.5
+title: "Fix: Display toggle (grid/list) triggers full DB reload"
+status: To Do
+assignee: []
+created_date: "2026-05-19 11:45"
+labels:
+  - perf
+  - fix
+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/index.ex
+  - lib/music_library_web/live/wishlist_live/index.ex
+parent_task_id: ML-169
+priority: high
+ordinal: 26000
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+
+Fix performance issue where toggling between grid and list display views triggers a full FTS database reload.
+
+## Problem
+
+`handle_set_display` in `index_actions.ex` calls `load_and_assign_records/2` which re-executes the full FTS search query (`search_records_count` + `search_records`). The toggle only changes a CSS layout class (`@display == :grid` vs `@display == :list`) — no data changes.
+
+## Impact
+
+Every grid/list toggle wastes 2 FTS queries. This is a common user interaction (clicking the view switcher button).
+
+## Files
+
+- `lib/music_library_web/live_helpers/index_actions.ex:136-143` — `handle_set_display/2` calls `load_and_assign_records`
+- `lib/music_library_web/live/collection_live/index.ex:336` — `handle_event("set_display")`
+- `lib/music_library_web/live/wishlist_live/index.ex:259` — `handle_event("set_display")`
+
+## Fix
+
+Remove the `load_and_assign_records` call from `handle_set_display`. Only `assign(:display, mode)` is needed. The existing `:if={@display == :grid}` / `:if={@display == :list}` conditionals already handle showing/hiding the appropriate view.
+
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+
+<!-- AC:BEGIN -->
+
+- [ ] #1 Grid/list toggle no longer triggers DB queries (verified via QueryReporter)
+- [ ] #2 Grid view renders correctly after toggle
+- [ ] #3 List view renders correctly after toggle
+- [ ] #4 No regression in search/filter functionality after toggle
+<!-- AC:END -->