ML-190: add same-record reconnect optimization task

From audit doc-25 (Phase 2), Recommendation #2.

backlog/tasks/ml-190 - Skip-redundant-unsubscriberesubscribe-on-same-record-reconnect.md

@@ -0,0 +1,41 @@
+---
+id: ML-190
+title: Skip redundant unsubscribe+resubscribe on same-record reconnect
+status: To Do
+assignee: []
+created_date: "2026-05-19 08:42"
+labels:
+  - audit
+  - pubsub
+  - optimization
+dependencies: []
+documentation:
+  - >-
+    audits/phase2-pubsub-lifecycle/doc-25 -
+    Audit-Report-PubSub-Subscription-Lifecycle-Phase-2.md
+modified_files:
+  - lib/music_library_web/live_helpers/record_actions.ex
+priority: low
+ordinal: 25000
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+
+`RecordActions.manage_subscription/2` unsubscribes the old record and subscribes the new record on every `handle_params` call. When LiveView reconnects to the same record (e.g., after a WebSocket drop within the reconnect grace period), it unsubscribes and resubscribes to the same topic. While harmless (Phoenix.PubSub deduplicates by PID), a same-record check would be a micro-optimization.
+
+**Fix:** Add a guard: `if socket.assigns[:record] && socket.assigns.record.id != new_id, do: Records.unsubscribe(...)` — only unsubscribe when the record actually changes.
+
+**Source:** Audit doc-25 (Phase 2), Recommendation #2.
+
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+
+<!-- AC:BEGIN -->
+
+- [ ] #1 manage_subscription/2 only calls unsubscribe when old record ID differs from new ID
+- [ ] #2 Same-record reconnect skips unsubscribe+resubscribe entirely
+- [ ] #3 All existing tests pass
+<!-- AC:END -->