refactor: extract shared mixins and helpers, drop dead abstractions

Introduces shared seams for paginated views, D-pad reorder, media control
routing, async singletons and the device method channel, then points the
open-coded copies at them.

Also removes unused models and duplicated provider/server plumbing, folds
the twice-implemented artifact store in the server, and factors the
repeated Flutter toolchain prologue in CI into a composite action.

lib/mixins/deletion_aware.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 import 'package:flutter/material.dart';
 import '../utils/deletion_notifier.dart';
 import 'event_aware.dart';
+import 'watch_state_aware.dart';
 
 /// Mixin for screens that need to react to deletion events.
 ///
@@ -74,3 +75,21 @@ mixin DeletionAware<T extends StatefulWidget> on State<T> {
     super.dispose();
   }
 }
+
+/// Points [DeletionAware]'s filters at the [WatchStateAware] ones.
+///
+/// The usual case: a screen shows the same rows for both event families, so a
+/// deleted show and a watched show affect exactly the same items. Mix this in
+/// after both aware mixins instead of re-typing the three getters. A screen
+/// that genuinely needs a different scope overrides the getter it cares about
+/// (or skips this mixin entirely).
+mixin DeletionMirrorsWatchState<T extends StatefulWidget> on WatchStateAware<T>, DeletionAware<T> {
+  @override
+  String? get deletionServerId => watchStateServerId;
+
+  @override
+  Set<String>? get deletionGlobalKeys => watchedGlobalKeys;
+
+  @override
+  Set<String>? get deletionIds => watchedIds;
+}

lib/mixins/paginated_item_loader.dart

@@ -104,43 +104,6 @@ mixin PaginatedItemLoader<T, W extends StatefulWidget> on State<W> {
     return (page: result, applied: true);
   }
 
-  /// Shared initial-load transaction for paginated consumers.
-  ///
-  /// Owns reset, stale-result rejection, mounted checks, and error-state
-  /// application. Callers supply only their view fields, logging, and
-  /// post-success behavior.
-  Future<bool> loadInitialPaginatedItems({
-    required int pageSize,
-    required VoidCallback resetViewState,
-    required void Function(List<T> items) applyLoadedItems,
-    required void Function(Object error, StackTrace stackTrace) applyError,
-    void Function(int loadedCount, int totalCount)? onLoaded,
-    void Function(Object error, StackTrace stackTrace)? onError,
-  }) async {
-    setState(() {
-      resetViewState();
-      resetPaginationState();
-    });
-
-    try {
-      final initialPage = await loadInitialPageWithStatus(pageSize);
-      if (!initialPage.applied || !mounted) return false;
-
-      setState(() {
-        applyLoadedItems(loadedItems.values.toList());
-      });
-      onLoaded?.call(loadedItems.length, totalSize);
-      return true;
-    } catch (error, stackTrace) {
-      onError?.call(error, stackTrace);
-      if (!mounted) return false;
-      setState(() {
-        applyError(error, stackTrace);
-      });
-      return false;
-    }
-  }
-
   /// Fetch any unloaded items inside [firstIndex, firstIndex + visibleCount)
   /// with [buffer] extra indices on each side. Serialized — only one
   /// range-fetch runs at a time — and re-checks after each success so a

lib/mixins/standard_paginated_view.dart

@@ -0,0 +1,74 @@
+import 'package:flutter/widgets.dart';
+
+import '../media/media_item.dart';
+import 'item_updatable.dart';
+import 'paginated_item_loader.dart';
+
+/// Standard view-state wiring for screens whose body is a single paginated
+/// list.
+///
+/// [PaginatedItemLoader] owns the sparse `loadedItems` map; the hosts
+/// (`BaseMediaListDetailScreen`, `BaseLibraryTabState`) additionally expose
+/// `items` / `isLoading` / `errorMessage` to drive the loading, empty and
+/// error chrome. This mixin owns the transitions between the two, so a
+/// screen's `loadItems` supplies only the page size, the error text, and an
+/// optional post-load hook.
+mixin StandardPaginatedView<T, W extends StatefulWidget> on PaginatedItemLoader<T, W> {
+  set items(List<T> value);
+  set isLoading(bool value);
+  set errorMessage(String? value);
+
+  /// Initial-load transaction: clears the view state, fetches the first page,
+  /// then publishes either the loaded items or [errorMessageFor]'s text.
+  ///
+  /// Stale results — a newer load started, or the screen was disposed — are
+  /// dropped without touching state. [errorMessageFor] runs even when
+  /// unmounted, so screens can log from it; [onLoaded] runs only after a
+  /// successful publish.
+  Future<void> loadStandardPaginatedItems({
+    required int pageSize,
+    required String Function(Object error, StackTrace stackTrace) errorMessageFor,
+    void Function(int loadedCount, int totalCount)? onLoaded,
+  }) async {
+    setState(() {
+      isLoading = true;
+      errorMessage = null;
+      items = [];
+      resetPaginationState();
+    });
+
+    try {
+      final initialPage = await loadInitialPageWithStatus(pageSize);
+      if (!initialPage.applied || !mounted) return;
+
+      setState(() {
+        items = loadedItems.values.toList();
+        isLoading = false;
+      });
+      onLoaded?.call(loadedItems.length, totalSize);
+    } catch (error, stackTrace) {
+      final message = errorMessageFor(error, stackTrace);
+      if (!mounted) return;
+      setState(() {
+        errorMessage = message;
+        isLoading = false;
+      });
+    }
+  }
+}
+
+/// [ItemUpdatable.updateItemInLists] for screens whose visible list is the
+/// sparse `loadedItems` map rather than a flat `items` list — searching the
+/// map is what keeps an item refreshed at a scrolled-in position, past the
+/// first page.
+mixin PaginatedItemUpdatable<W extends StatefulWidget> on PaginatedItemLoader<MediaItem, W>, ItemUpdatable<W> {
+  @override
+  void updateItemInLists(String sourceGlobalKey, MediaItem updatedItem) {
+    for (final entry in loadedItems.entries) {
+      if (entry.value.globalKey == sourceGlobalKey) {
+        loadedItems[entry.key] = updatedItem;
+        return;
+      }
+    }
+  }
+}