cover Vim edit-ops and extension edge branches

Lift line coverage back over the 95% floor after the Flutter 3.44.1
merge nudged it to 94.99%. Adds tests for the changeWord/no-op-edit/
empty-paste/word-motion-edge branches in vim_edit_ops, the lone-key
flush path in SequenceMatcher, and the keybindings-ui / vim extension
identity + deactivate paths.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/builtin/editor/vim_edit_ops_test.dart

@@ -149,6 +149,43 @@ void main() {
       expect(r.enterInsert, isTrue);
       expect(r.register?.linewise, isTrue);
     });
+
+    test('cw deletes to the next word and enters insert', () {
+      final r = applyVim(VimAction.changeWord, _tev('hello world', 0));
+      expect(r.value.text, 'world');
+      expect(r.enterInsert, isTrue);
+      expect(r.register?.text, 'hello ');
+    });
+
+    test('x at the line end is a no-op', () {
+      final r = applyVim(VimAction.deleteChar, _tev('ab\ncd', 2)); // caret on the newline
+      expect(r.value.text, 'ab\ncd');
+      expect(r.register, isNull);
+    });
+
+    test('D at the line end is a no-op', () {
+      final r = applyVim(VimAction.deleteToEnd, _tev('ab', 2));
+      expect(r.value.text, 'ab');
+    });
+
+    test('p with an empty register does nothing', () {
+      final r = applyVim(VimAction.paste, _tev('ab', 0));
+      expect(r.value.text, 'ab');
+    });
+  });
+
+  group('word-motion edges', () {
+    test('w / b cross punctuation and underscores as their own class', () {
+      // foo_bar is one word (underscore is a word char); the dot is punct.
+      const t = 'foo_bar.baz';
+      expect(applyVim(VimAction.wordForward, _tev(t, 0)).value.selection.extentOffset, 7); // the '.'
+      expect(applyVim(VimAction.wordBackward, _tev(t, 8)).value.selection.extentOffset, 7);
+    });
+
+    test('e on the last word clamps to the final char', () {
+      final r = applyVim(VimAction.wordEnd, _tev('hi', 1));
+      expect(r.value.selection.extentOffset, 1);
+    });
   });
 
   group('insert entry', () {

test/builtin/keybindings_ui/preset_commands_test.dart

@@ -17,6 +17,20 @@ void main() {
   });
   tearDown(() => f.dispose());
 
+  test('identifies itself', () {
+    final ext = KeybindingsUiExtension();
+    expect(ext.id, 'builtin.keybindings-ui');
+    expect(ext.title, 'Keybindings UI');
+    expect(ext.version, '0.1.0');
+  });
+
+  test('deactivate drops the keymap reference', () async {
+    await f.services.extensions.deactivate('builtin.keybindings-ui');
+    // Re-activating is clean (no retained state).
+    await f.services.extensions.activate('builtin.keybindings-ui');
+    expect(f.services.commands.get('keymap.preset.vim'), isNotNull);
+  });
+
   test('contributes a switch command per shipped preset', () {
     expect(f.services.commands.get('keymap.preset.vim'), isNotNull);
     expect(f.services.commands.get('keymap.preset.default'), isNotNull);

test/builtin/vim/vim_extension_test.dart

@@ -22,6 +22,12 @@ void main() {
 
   bool flag(String name) => f.services.keymap.scope[name] ?? false;
 
+  test('identifies itself', () {
+    expect(ext.id, 'builtin.vim');
+    expect(ext.title, 'Vim');
+    expect(ext.version, '0.1.0');
+  });
+
   test('inert under the default preset', () async {
     await f.services.extensions.activate('builtin.vim');
     expect(ext.modeService!.enabled, isFalse);

test/kernel/src/keymap/sequence_matcher_test.dart

@@ -171,5 +171,13 @@ void main() {
     test('flush with nothing buffered is a no-op', () {
       expect(matcher.flush().outcome, SeqOutcome.pending);
     });
+
+    test('flush of a lone prefix key (no exact) passes it through', () {
+      // `g` is a pure prefix of `g g` with no single-`g` binding.
+      expect(feed('g').outcome, SeqOutcome.pending);
+      final r = matcher.flush();
+      expect(r.outcome, SeqOutcome.unmatched);
+      expect(r.passKey, KeyChord.parse('g'));
+    });
   });
 }