ML-188: guard PubSub record updates during edit mode

Add live_action guard to handle_info({:update, record}) in both
CollectionLive.Show and WishlistLive.Show. When the user is editing,
background worker updates are skipped and a warning toast is shown
instead of overwriting the socket. Normal show-mode updates and
mismatched-ID no-ops are unchanged.

6 tests added covering all three code paths.

lib/music_library_web/live/collection_live/show.ex

@@ -472,13 +472,25 @@ defmodule MusicLibraryWeb.CollectionLive.Show do
 
   @impl true
   def handle_info({:update, record}, socket) do
-    if record.id == socket.assigns.record.id do
-      {:noreply,
-       socket
-       |> RecordActions.handle_record_updated(record)
-       |> assign_similar_records()}
-    else
-      {:noreply, socket}
+    cond do
+      record.id != socket.assigns.record.id ->
+        {:noreply, socket}
+
+      socket.assigns.live_action == :edit ->
+        {:noreply,
+         socket
+         |> put_toast(
+           :warning,
+           gettext(
+             "Record was updated in the background. Your edits may be stale — save and re-open to see the latest data."
+           )
+         )}
+
+      true ->
+        {:noreply,
+         socket
+         |> RecordActions.handle_record_updated(record)
+         |> assign_similar_records()}
     end
   end
 

lib/music_library_web/live/wishlist_live/show.ex

@@ -365,10 +365,22 @@ defmodule MusicLibraryWeb.WishlistLive.Show do
 
   @impl true
   def handle_info({:update, record}, socket) do
-    if record.id == socket.assigns.record.id do
-      {:noreply, RecordActions.handle_record_updated(socket, record)}
-    else
-      {:noreply, socket}
+    cond do
+      record.id != socket.assigns.record.id ->
+        {:noreply, socket}
+
+      socket.assigns.live_action == :edit ->
+        {:noreply,
+         socket
+         |> put_toast(
+           :warning,
+           gettext(
+             "Record was updated in the background. Your edits may be stale — save and re-open to see the latest data."
+           )
+         )}
+
+      true ->
+        {:noreply, RecordActions.handle_record_updated(socket, record)}
     end
   end
 

lib/music_library_web/live_helpers/record_actions.ex

@@ -119,6 +119,10 @@ defmodule MusicLibraryWeb.LiveHelpers.RecordActions do
   @doc """
   Handles a background record update. Returns the updated socket (not wrapped
   in `{:noreply, ...}`) so the caller can pipe additional assigns.
+
+  **Note:** Callers intentionally bypass this function when `live_action == :edit`
+  to prevent background worker updates from overwriting the user's in-progress
+  form edits. See CollectionLive.Show and WishlistLive.Show `handle_info({:update, record})`.
   """
   def handle_record_updated(socket, record) do
     socket