dispose-safe teardown for KeymapService + ClaudeConfig; cover the

claude extension lifecycle

make test-integration failed at widget-tree finalization: the
palette's dispose() clears its scope flag, which during app teardown
runs AFTER KernelServices.dispose() has disposed the KeymapService —
notifyListeners asserted. Scope-flag mutations now use the same
fire-and-forget guard SettingsStore established. Same family in
ClaudeConfig: activation's unawaited load() could notify (and start
watchers on) a disposed notifier when a teardown raced it.

The claude extension's activation lifecycle and command success paths
are now exercised end-to-end through the kernel fixture — the file
entered the coverage denominator with the T-391 failure-path tests,
so per the ratchet discipline the rest of it gets covered too.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/kernel/src/keymap/keymap_service.dart

@@ -167,20 +167,37 @@ class KeymapService extends ChangeNotifier {
     return km.match(sequence, _scope).exact;
   }
 
+  /// Scope-flag producers clear their flags from widget dispose() — which
+  /// during app teardown runs AFTER KernelServices.dispose() has disposed
+  /// this notifier. Tolerate that ordering instead of asserting (the same
+  /// fire-and-forget pattern SettingsStore uses).
+  bool _disposed = false;
+
+  @override
+  void dispose() {
+    _disposed = true;
+    super.dispose();
+  }
+
+  void _safeNotify() {
+    if (_disposed) return;
+    notifyListeners();
+  }
+
   /// Set a named scope flag. Producers should call this when their
   /// state changes so when-clauses re-evaluate correctly. Notifies
   /// listeners when the value actually changes.
   void setScopeFlag(String name, bool value) {
     if (_scope[name] == value) return;
     _scope[name] = value;
-    notifyListeners();
+    _safeNotify();
   }
 
   /// Clear a named scope flag.
   void clearScopeFlag(String name) {
     if (!_scope.containsKey(name)) return;
     _scope.remove(name);
-    notifyListeners();
+    _safeNotify();
   }
 
   /// Switch presets. Persists the new preset name to settings and