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/builtin/claude/src/claude_config.dart

@@ -253,6 +253,7 @@ class ClaudeConfig extends ChangeNotifier {
     _version = _parseVersion(await _guard(_versionRunner));
     await _readProbeCache();
     await _loadDiskConfig();
+    if (_disposed) return; // activation fired-and-forgot; teardown won
     _startWatchers();
     notifyListeners();
   }
@@ -296,8 +297,14 @@ class ClaudeConfig extends ChangeNotifier {
     notifyListeners();
   }
 
+  /// Set when [dispose] runs. The fire-and-forget [load] from extension
+  /// activation checks this so a teardown racing an in-flight load can't
+  /// notify (or start watchers on) a disposed notifier.
+  bool _disposed = false;
+
   @override
   void dispose() {
+    _disposed = true;
     _stopWatching();
     super.dispose();
   }