add multi-file editor tabs

The editor pane showed a single buffer — opening a second file
replaced the first, even though the daemon's EditorRegistry has
always been multi-buffer (editor.list / activate / close). This wires
the UI up to that: EditorController now tracks the full open-buffer
list (via editor.list on hydrate, kept in sync by editor.opened /
closed / saved / edited events), and EditorView renders the buffers
as tabs through the shared MultitabPane — the same strip the Claude
pane uses. The daemon stays the source of truth: the local tab
controller is reconciled from it, and tab select / close route back
as editor.activate / editor.close. Reorder is disabled for now
(daemon order is authoritative).

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

CHANGELOG.md

@@ -18,6 +18,11 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Added
 
+- Multi-file editor tabs — the editor pane now shows one tab per open
+  buffer (filename + a dot when unsaved) via the shared tab strip;
+  opening a second file no longer replaces the first. Click a tab to
+  switch, × to close. Backed by the daemon's existing multi-buffer
+  model.
 - Typed IPC command-schema framework (T-119/T-120, D-74) — commands
   register an argument schema beside their handler; the dispatcher
   normalises argv into named args, coerces types, and validates

lib/builtin/editor/src/editor_controller.dart

@@ -16,6 +16,11 @@ import 'package:clide/clide.dart';
 import 'package:clide/kernel/kernel.dart';
 import 'package:flutter/foundation.dart';
 
+/// Lightweight view of one open buffer for the tab strip — the
+/// daemon's authoritative content lives behind [EditorController];
+/// this is just what the tabs need to render.
+typedef OpenBuffer = ({String id, String path, bool dirty});
+
 class EditorController extends ChangeNotifier {
   EditorController({required this.ipc, required DaemonBus events}) {
     _eventSub = events.on<DaemonEvent>().listen(_onEvent);
@@ -32,6 +37,9 @@ class EditorController extends ChangeNotifier {
   bool _dirty = false;
   String? _error;
 
+  /// All open buffers, in daemon order, for the tab strip.
+  List<OpenBuffer> _buffers = const [];
+
   bool _suppressNextRemoteEdit = false;
   int _pendingLocalEdits = 0;
 
@@ -41,10 +49,12 @@ class EditorController extends ChangeNotifier {
   Selection get selection => _selection;
   bool get dirty => _dirty;
   String? get error => _error;
+  List<OpenBuffer> get buffers => _buffers;
 
-  /// On first mount we don't know what (if anything) is already
-  /// active. Ask the daemon.
+  /// On first mount we don't know what's already open. Ask the daemon
+  /// for the buffer list and the active buffer.
   Future<void> hydrate() async {
+    await _refreshList();
     final r = await ipc.request('editor.active');
     if (!r.ok) {
       _error = r.error?.message;
@@ -63,6 +73,52 @@ class EditorController extends ChangeNotifier {
     await _loadBuffer(id);
   }
 
+  /// Make [id] the active buffer. The daemon echoes an
+  /// `editor.active-changed` event which loads its content.
+  Future<void> activate(String id) async {
+    if (id == _activeId) return;
+    await ipc.request('editor.activate', args: {'id': id});
+  }
+
+  /// Close the buffer [id]. The daemon emits `editor.closed` (and an
+  /// `editor.active-changed` if it was the active one).
+  Future<void> closeBuffer(String id) async {
+    await ipc.request('editor.close', args: {'id': id});
+  }
+
+  /// Re-fetch the open-buffer list from the daemon (authoritative).
+  Future<void> _refreshList() async {
+    final r = await ipc.request('editor.list');
+    if (!r.ok) return;
+    final raw = r.data['buffers'];
+    if (raw is! List) return;
+    _buffers = [
+      for (final b in raw)
+        if (b is Map)
+          (
+            id: b['id']! as String,
+            path: b['path']! as String,
+            dirty: (b['dirty'] as bool?) ?? false,
+          ),
+    ];
+    notifyListeners();
+  }
+
+  void _markDirty(String id, bool dirty) {
+    var changed = false;
+    _buffers = [
+      for (final b in _buffers)
+        if (b.id == id && b.dirty != dirty)
+          (() {
+            changed = true;
+            return (id: b.id, path: b.path, dirty: dirty);
+          })()
+        else
+          b,
+    ];
+    if (changed) notifyListeners();
+  }
+
   Future<void> _loadBuffer(String id) async {
     final r = await ipc.request('editor.read', args: {'id': id});
     if (!r.ok) {
@@ -91,6 +147,7 @@ class EditorController extends ChangeNotifier {
     _content = newContent;
     _selection = newSelection;
     _dirty = true;
+    _markDirty(id, true);
     notifyListeners();
 
     // Mirror to daemon. Use editor.set-content for the first cut —
@@ -116,15 +173,19 @@ class EditorController extends ChangeNotifier {
     if (e.subsystem != 'editor') return;
     switch (e.kind) {
       case 'editor.opened':
+        // A new buffer joined the set — refresh the tab list, then
+        // load whatever the daemon now considers active.
+        unawaited(_refreshList());
+        final id = e.data['id'] as String?;
+        if (id == null) {
+          _clearActive();
+        } else if (id != _activeId) {
+          _loadBuffer(id);
+        }
       case 'editor.active-changed':
         final id = e.data['id'] as String?;
         if (id == null) {
-          _activeId = null;
-          _activePath = null;
-          _content = '';
-          _selection = const Selection.collapsed(0);
-          _dirty = false;
-          notifyListeners();
+          _clearActive();
         } else if (id != _activeId) {
           _loadBuffer(id);
         }
@@ -138,25 +199,37 @@ class EditorController extends ChangeNotifier {
         // Remote edit (another client, or the CLI inserting bytes).
         // Reload the authoritative buffer.
         final id = e.data['id'] as String?;
+        if (id != null) _markDirty(id, true);
         if (id != null && id == _activeId && _pendingLocalEdits == 0) {
           _loadBuffer(id);
         }
       case 'editor.saved':
-        if (e.data['id'] == _activeId) {
+        final id = e.data['id'] as String?;
+        if (id != null) _markDirty(id, false);
+        if (id == _activeId) {
           _dirty = false;
           notifyListeners();
         }
       case 'editor.closed':
+        // A buffer left the set — refresh the tab list. If it was the
+        // active one the daemon promotes another and emits
+        // active-changed; reflect the cleared state in the meantime.
+        unawaited(_refreshList());
         if (e.data['id'] == _activeId) {
-          _activeId = null;
-          _activePath = null;
-          _content = '';
-          _dirty = false;
-          notifyListeners();
+          _clearActive();
         }
     }
   }
 
+  void _clearActive() {
+    _activeId = null;
+    _activePath = null;
+    _content = '';
+    _selection = const Selection.collapsed(0);
+    _dirty = false;
+    notifyListeners();
+  }
+
   @override
   void dispose() {
     _eventSub?.cancel();

lib/builtin/editor/src/editor_view.dart

@@ -10,10 +10,13 @@ import 'package:flutter/widgets.dart';
 import 'editor_controller.dart';
 import 'syntax_text_controller.dart';
 
-/// Tier-2 editor tab. One tab — the content reflects the daemon's
-/// active buffer. Multi-file tabs live in the workspace-slot plan but
-/// aren't in Tier 2's scope; opening a new file swaps this view's
-/// content.
+/// Tier-2 editor pane. Shows one tab per open buffer via the shared
+/// [MultitabPane] (the same strip the Claude pane uses); the body
+/// reflects the daemon's active buffer. The daemon ([EditorRegistry])
+/// is the source of truth for which buffers are open and which is
+/// active — the local [MultitabController] is reconciled from it, and
+/// tab gestures (select / close) are routed back as `editor.activate`
+/// / `editor.close`.
 ///
 /// Uses Flutter's low-level `EditableText` so we stay off Material
 /// per D-007. Owning more of the editor stack (line numbers, gutter,
@@ -27,17 +30,24 @@ class EditorView extends StatefulWidget {
 
 class _EditorViewState extends State<EditorView> {
   EditorController? _controller;
+  final MultitabController<String> _tabs = MultitabController<String>();
   final TreeSitterService _syntax = TreeSitterService.shared;
   late final SyntaxTextController _text;
   late final FocusNode _focus;
   String? _lastRemoteContent;
 
+  /// Guards the controller→tabstrip reconcile so the tabstrip's own
+  /// change notifications (from us mutating it) don't bounce back as
+  /// daemon calls.
+  bool _applyingRemote = false;
+
   @override
   void initState() {
     super.initState();
     _text = SyntaxTextController(syntax: _syntax);
     _focus = FocusNode();
     _text.addListener(_onTextChanged);
+    _tabs.addListener(_onTabsChanged);
   }
 
   @override
@@ -54,6 +64,8 @@ class _EditorViewState extends State<EditorView> {
     _text.removeListener(_onTextChanged);
     _text.dispose();
     _focus.dispose();
+    _tabs.removeListener(_onTabsChanged);
+    _tabs.dispose();
     _controller?.removeListener(_onControllerChanged);
     _controller?.dispose();
     super.dispose();
@@ -61,6 +73,7 @@ class _EditorViewState extends State<EditorView> {
 
   void _onControllerChanged() {
     final c = _controller!;
+    _syncTabs(c);
     _text.updatePath(c.activePath);
     if (c.content != _lastRemoteContent) {
       _lastRemoteContent = c.content;
@@ -72,7 +85,46 @@ class _EditorViewState extends State<EditorView> {
       _text.value = TextEditingValue(text: c.content, selection: sel);
       _text.addListener(_onTextChanged);
     }
-    setState(() {}); // subtitle refresh
+    setState(() {}); // tab/title refresh
+  }
+
+  /// Reconcile the local tab strip to match the daemon's open-buffer
+  /// list + active selection. Membership and order follow the daemon;
+  /// titles carry a dirty marker.
+  void _syncTabs(EditorController c) {
+    _applyingRemote = true;
+    final bufs = c.buffers;
+    final liveIds = {for (final b in bufs) b.id};
+    for (final e in _tabs.entries) {
+      if (!liveIds.contains(e.id)) _tabs.remove(e.id);
+    }
+    for (final b in bufs) {
+      final title = _tabTitle(b);
+      final existing = _tabs.entries.where((e) => e.id == b.id).toList();
+      if (existing.isEmpty) {
+        _tabs.add(MultitabEntry<String>(id: b.id, title: title, payload: b.id), activate: false);
+      } else if (existing.first.title != title) {
+        _tabs.replace(b.id, MultitabEntry<String>(id: b.id, title: title, payload: b.id));
+      }
+    }
+    final act = c.activeId;
+    if (act != null && _tabs.activeId != act) _tabs.activate(act);
+    _applyingRemote = false;
+  }
+
+  /// User tapped a tab. The tab strip already updated its local active
+  /// selection; mirror that choice to the daemon.
+  void _onTabsChanged() {
+    if (_applyingRemote) return;
+    final id = _tabs.activeId;
+    if (id != null && id != _controller?.activeId) {
+      unawaited(_controller?.activate(id) ?? Future.value());
+    }
+  }
+
+  String _tabTitle(OpenBuffer b) {
+    final name = b.path.split('/').last;
+    return b.dirty ? '$name •' : name;
   }
 
   void _onTextChanged() {
@@ -112,32 +164,29 @@ class _EditorViewState extends State<EditorView> {
     return ListenableBuilder(
       listenable: c,
       builder: (context, _) {
-        final title = c.activePath ?? 'editor';
-        final subtitle = c.activeId == null
-            ? 'no buffer · use `clide open <path>` or pick a file in the tree'
-            : '${c.activeId} · ${c.dirty ? 'modified' : 'saved'}'
-                '${c.error == null ? '' : ' · ${c.error}'}';
-
-        return ClidePaneChrome(
-          title: title,
-          subtitle: subtitle,
-          child: c.activeId == null
-              ? const Center(
-                  child: ClideText(
-                    'Open a file to begin editing.',
-                    muted: true,
-                  ),
-                )
-              : Focus(
-                  onKeyEvent: _onKey,
-                  child: _TextBody(
-                    controller: _text,
-                    focus: _focus,
-                    background: tokens.panelBackground,
-                    foreground: tokens.globalForeground,
-                    accent: tokens.globalFocus,
-                  ),
-                ),
+        if (c.buffers.isEmpty) {
+          return ClidePaneChrome(
+            title: 'editor',
+            subtitle: 'no buffer · use `clide open <path>` or pick a file in the tree',
+            child: const Center(
+              child: ClideText('Open a file to begin editing.', muted: true),
+            ),
+          );
+        }
+        return MultitabPane<String>(
+          controller: _tabs,
+          allowReorder: false,
+          onCloseRequested: (entry) => unawaited(c.closeBuffer(entry.id)),
+          bodyBuilder: (context, _) => Focus(
+            onKeyEvent: _onKey,
+            child: _TextBody(
+              controller: _text,
+              focus: _focus,
+              background: tokens.panelBackground,
+              foreground: tokens.globalForeground,
+              accent: tokens.globalFocus,
+            ),
+          ),
         );
       },
     );

test/builtin/editor/editor_controller_test.dart

@@ -0,0 +1,255 @@
+/// Tests the multi-buffer tracking in EditorController (the UI mirror
+/// of the daemon's editor model): hydrate populates the open-buffer
+/// list, events keep it in sync, and activate/close route to IPC.
+library;
+
+import 'package:clide/builtin/editor/src/editor_controller.dart';
+import 'package:clide/clide.dart';
+import 'package:clide/kernel/kernel.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../../helpers/fake_ipc.dart';
+
+IpcResponse _ok(Map<String, Object?> data) => IpcResponse.ok(id: '', data: data);
+
+Map<String, Object?> _buf(String id, String path, {bool dirty = false}) => {'id': id, 'path': path, 'dirty': dirty};
+
+Map<String, Object?> _read(String id, String path, String content, {bool dirty = false}) => {
+      'id': id,
+      'path': path,
+      'content': content,
+      'selection': {'start': 0, 'end': 0},
+      'dirty': dirty,
+    };
+
+void emitEditor(DaemonBus bus, String kind, Map<String, Object?> data) {
+  bus.emit(DaemonEvent(subsystem: 'editor', kind: kind, data: data, ts: DateTime.now().toUtc()));
+}
+
+void main() {
+  late DaemonBus bus;
+  late FakeDaemonClient ipc;
+  late EditorController c;
+
+  setUp(() {
+    bus = DaemonBus();
+    ipc = FakeDaemonClient(log: Logger(), events: bus);
+    c = EditorController(ipc: ipc, events: bus);
+  });
+
+  tearDown(() async {
+    c.dispose();
+    await bus.dispose();
+  });
+
+  group('hydrate', () {
+    test('populates the open-buffer list and loads the active buffer', () async {
+      ipc.stub(
+          'editor.list',
+          (_) async => _ok({
+                'buffers': [_buf('b_1', 'lib/a.dart'), _buf('b_2', 'lib/b.dart', dirty: true)]
+              }));
+      ipc.stub(
+          'editor.active',
+          (_) async => _ok({
+                'active': {'id': 'b_1'}
+              }));
+      ipc.stub('editor.read', (a) async => _ok(_read('b_1', 'lib/a.dart', 'hello')));
+
+      await c.hydrate();
+
+      expect(c.buffers.map((b) => b.id).toList(), ['b_1', 'b_2']);
+      expect(c.buffers[1].dirty, isTrue);
+      expect(c.activeId, 'b_1');
+      expect(c.content, 'hello');
+    });
+
+    test('with no active buffer leaves the list but no active content', () async {
+      ipc.stub(
+          'editor.list',
+          (_) async => _ok({
+                'buffers': [_buf('b_1', 'lib/a.dart')]
+              }));
+      ipc.stub('editor.active', (_) async => _ok(const {})); // no `active` key
+
+      await c.hydrate();
+
+      expect(c.buffers, hasLength(1));
+      expect(c.activeId, isNull);
+      expect(c.content, '');
+    });
+  });
+
+  group('routing tab gestures to IPC', () {
+    test('activate(id) issues editor.activate', () async {
+      String? activated;
+      ipc.stub('editor.activate', (a) async {
+        activated = a['id'] as String?;
+        return _ok({'active': a['id']});
+      });
+      await c.activate('b_7');
+      expect(activated, 'b_7');
+    });
+
+    test('activate is a no-op when the id is already active', () async {
+      ipc.stub(
+          'editor.list',
+          (_) async => _ok({
+                'buffers': [_buf('b_1', 'a.dart')]
+              }));
+      ipc.stub(
+          'editor.active',
+          (_) async => _ok({
+                'active': {'id': 'b_1'}
+              }));
+      ipc.stub('editor.read', (_) async => _ok(_read('b_1', 'a.dart', 'x')));
+      await c.hydrate();
+
+      var calls = 0;
+      ipc.stub('editor.activate', (a) async {
+        calls++;
+        return _ok({'active': a['id']});
+      });
+      await c.activate('b_1'); // already active
+      expect(calls, 0);
+    });
+
+    test('closeBuffer(id) issues editor.close', () async {
+      String? closed;
+      ipc.stub('editor.close', (a) async {
+        closed = a['id'] as String?;
+        return _ok(const {});
+      });
+      await c.closeBuffer('b_3');
+      expect(closed, 'b_3');
+    });
+  });
+
+  group('event sync', () {
+    test('editor.opened refreshes the list and loads the new active buffer', () async {
+      var listVersion = 1;
+      ipc.stub(
+          'editor.list',
+          (_) async => _ok({
+                'buffers': listVersion == 1 ? [_buf('b_1', 'a.dart')] : [_buf('b_1', 'a.dart'), _buf('b_2', 'b.dart')]
+              }));
+      ipc.stub(
+          'editor.active',
+          (_) async => _ok({
+                'active': {'id': 'b_1'}
+              }));
+      ipc.stub('editor.read', (a) async {
+        final id = a['id'] as String;
+        return _ok(_read(id, id == 'b_1' ? 'a.dart' : 'b.dart', 'content-$id'));
+      });
+      await c.hydrate();
+      expect(c.buffers, hasLength(1));
+
+      listVersion = 2;
+      emitEditor(bus, 'editor.opened', {'id': 'b_2'});
+      await pumpEventQueue();
+
+      expect(c.buffers.map((b) => b.id).toList(), ['b_1', 'b_2']);
+      expect(c.activeId, 'b_2');
+      expect(c.content, 'content-b_2');
+    });
+
+    test('editor.closed refreshes the list and clears active when it was active', () async {
+      var listVersion = 1;
+      ipc.stub(
+          'editor.list',
+          (_) async => _ok({
+                'buffers': listVersion == 1 ? [_buf('b_1', 'a.dart'), _buf('b_2', 'b.dart')] : [_buf('b_2', 'b.dart')]
+              }));
+      ipc.stub(
+          'editor.active',
+          (_) async => _ok({
+                'active': {'id': 'b_1'}
+              }));
+      ipc.stub('editor.read', (a) async => _ok(_read(a['id'] as String, 'a.dart', 'x')));
+      await c.hydrate();
+      expect(c.buffers, hasLength(2));
+
+      listVersion = 2;
+      emitEditor(bus, 'editor.closed', {'id': 'b_1'});
+      await pumpEventQueue();
+
+      expect(c.buffers.map((b) => b.id).toList(), ['b_2']);
+      expect(c.activeId, isNull); // cleared until an active-changed arrives
+    });
+
+    test('editor.saved clears the dirty marker on the buffer', () async {
+      ipc.stub(
+          'editor.list',
+          (_) async => _ok({
+                'buffers': [_buf('b_1', 'a.dart', dirty: true)]
+              }));
+      ipc.stub(
+          'editor.active',
+          (_) async => _ok({
+                'active': {'id': 'b_1'}
+              }));
+      ipc.stub('editor.read', (_) async => _ok(_read('b_1', 'a.dart', 'x', dirty: true)));
+      await c.hydrate();
+      expect(c.buffers.single.dirty, isTrue);
+
+      emitEditor(bus, 'editor.saved', {'id': 'b_1'});
+      await pumpEventQueue();
+
+      expect(c.buffers.single.dirty, isFalse);
+      expect(c.dirty, isFalse);
+    });
+
+    test('editor.edited marks the buffer dirty', () async {
+      ipc.stub(
+          'editor.list',
+          (_) async => _ok({
+                'buffers': [_buf('b_1', 'a.dart')]
+              }));
+      ipc.stub(
+          'editor.active',
+          (_) async => _ok({
+                'active': {'id': 'b_1'}
+              }));
+      ipc.stub('editor.read', (_) async => _ok(_read('b_1', 'a.dart', 'x')));
+      await c.hydrate();
+      expect(c.buffers.single.dirty, isFalse);
+
+      // A remote edit (not our own — no set-content was issued).
+      emitEditor(bus, 'editor.edited', {'id': 'b_1'});
+      await pumpEventQueue();
+
+      expect(c.buffers.single.dirty, isTrue);
+    });
+  });
+
+  group('local edits', () {
+    test('pushLocalEdit marks the active buffer dirty and mirrors to IPC', () async {
+      ipc.stub(
+          'editor.list',
+          (_) async => _ok({
+                'buffers': [_buf('b_1', 'a.dart')]
+              }));
+      ipc.stub(
+          'editor.active',
+          (_) async => _ok({
+                'active': {'id': 'b_1'}
+              }));
+      ipc.stub('editor.read', (_) async => _ok(_read('b_1', 'a.dart', 'x')));
+      await c.hydrate();
+
+      Map<String, Object?>? setArgs;
+      ipc.stub('editor.set-content', (a) async {
+        setArgs = a;
+        return _ok(const {});
+      });
+      c.pushLocalEdit(newContent: 'xy', newSelection: const Selection.collapsed(2));
+      await pumpEventQueue();
+
+      expect(c.dirty, isTrue);
+      expect(c.buffers.single.dirty, isTrue);
+      expect(setArgs?['id'], 'b_1');
+      expect(setArgs?['text'], 'xy');
+    });
+  });
+}

test/builtin/editor/editor_view_test.dart

@@ -0,0 +1,86 @@
+/// Widget tests for the multi-tab editor view: a tab per open buffer
+/// (filename + dirty marker), the empty-state hint, and tab taps
+/// routing to `editor.activate`. Buffer-list logic itself is covered
+/// in editor_controller_test.dart.
+library;
+
+import 'package:clide/builtin/editor/src/editor_view.dart';
+import 'package:clide/clide.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../../helpers/kernel_fixture.dart';
+import '../../helpers/widget_harness.dart';
+
+IpcResponse _ok(Map<String, Object?> data) => IpcResponse.ok(id: '', data: data);
+
+Map<String, Object?> _buf(String id, String path, {bool dirty = false}) => {'id': id, 'path': path, 'dirty': dirty};
+
+Map<String, Object?> _read(String id, String path) => {
+      'id': id,
+      'path': path,
+      'content': 'content of $path',
+      'selection': {'start': 0, 'end': 0},
+      'dirty': false,
+    };
+
+void main() {
+  group('EditorView tabs', () {
+    late KernelFixture f;
+    setUp(() async => f = await KernelFixture.create());
+    tearDown(() => f.dispose());
+
+    void stubBuffers(List<Map<String, Object?>> buffers, {String? active}) {
+      f.ipc.stub('editor.list', (_) async => _ok({'buffers': buffers}));
+      f.ipc.stub(
+          'editor.active',
+          (_) async => active == null
+              ? _ok(const {})
+              : _ok({
+                  'active': {'id': active}
+                }));
+      f.ipc.stub('editor.read', (a) async {
+        final id = a['id'] as String;
+        final b = buffers.firstWhere((b) => b['id'] == id);
+        return _ok(_read(id, b['path'] as String));
+      });
+    }
+
+    testWidgets('renders one tab per open buffer, by filename', (tester) async {
+      stubBuffers([_buf('b_1', 'lib/a.dart'), _buf('b_2', 'src/b.dart')], active: 'b_1');
+      await tester.pumpWidget(harness(f, const EditorView()));
+      await tester.pumpAndSettle();
+      expect(find.text('a.dart'), findsOneWidget);
+      expect(find.text('b.dart'), findsOneWidget);
+    });
+
+    testWidgets('a dirty buffer carries a marker in its tab title', (tester) async {
+      stubBuffers([_buf('b_1', 'lib/a.dart', dirty: true)], active: 'b_1');
+      await tester.pumpWidget(harness(f, const EditorView()));
+      await tester.pumpAndSettle();
+      expect(find.text('a.dart •'), findsOneWidget);
+    });
+
+    testWidgets('no open buffers shows the open-a-file hint', (tester) async {
+      stubBuffers(const [], active: null);
+      await tester.pumpWidget(harness(f, const EditorView()));
+      await tester.pumpAndSettle();
+      expect(find.text('Open a file to begin editing.'), findsOneWidget);
+    });
+
+    testWidgets('tapping an inactive tab routes to editor.activate', (tester) async {
+      stubBuffers([_buf('b_1', 'lib/a.dart'), _buf('b_2', 'src/b.dart')], active: 'b_1');
+      String? activated;
+      f.ipc.stub('editor.activate', (a) async {
+        activated = a['id'] as String?;
+        return _ok({'active': a['id']});
+      });
+      await tester.pumpWidget(harness(f, const EditorView()));
+      await tester.pumpAndSettle();
+
+      await tester.tap(find.text('b.dart'));
+      await tester.pumpAndSettle();
+
+      expect(activated, 'b_2');
+    });
+  });
+}