add ClidePane primitive + focus-driven status-bar slot

Replace the MessageBus-based pane-context slot with a focus-driven one.
Panes keep their status widget locally; the FocusTracker holds the
focused pane's widget (activeStatusWidget) and ClidePane conveys it to
the shared slot only while its contribution is focused, re-conveying on
change and clearing on blur. The status-bar item just renders
focus.activeStatusWidget, height-clamped and marquee-scrolled when it
overflows. Removes the publish/subscribe race the bus version had.

T-150.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/builtin/claude/pane_context_status_test.dart

@@ -1,9 +1,11 @@
-/// Tests for the status-bar in-pane context slot (T-145): it shows the
-/// latest text published on the bus channel and clears on empty.
+/// Tests for the focus-driven status-bar slot item (T-150): it renders
+/// the focused pane's status widget and clears when focus moves to a
+/// pane with no status.
 library;
 
 import 'package:clide/builtin/claude/src/pane_context_status.dart';
-import 'package:clide/widgets/widgets.dart';
+import 'package:clide/kernel/src/panels/slot_id.dart';
+import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../../helpers/kernel_fixture.dart';
@@ -14,27 +16,20 @@ void main() {
   setUp(() async => f = await KernelFixture.create());
   tearDown(() => f.dispose());
 
-  testWidgets('renders the latest published context, clears on empty', (tester) async {
+  testWidgets('renders the focused pane status, clears on focus change', (tester) async {
     await tester.pumpWidget(harness(f, const PaneContextStatusItem()));
     await tester.pump();
-    expect(find.byType(ClideText), findsNothing); // nothing published yet
+    expect(find.text('S'), findsNothing); // nothing focused
 
-    publishPaneContext(f.services.messages, 'builtin.claude', 'opus 4.7  ·  default  ·  21k ctx');
+    final focus = f.services.focus;
+    focus.setActive(slot: Slots.workspace, contributionId: 'pane.x');
+    focus.setStatusWidget('pane.x', const Text('S', textDirection: TextDirection.ltr));
     await tester.pump();
-    await tester.pump();
-    expect(find.textContaining('opus 4.7'), findsOneWidget);
+    expect(find.text('S'), findsOneWidget);
 
-    // A newer publisher overwrites the slot.
-    publishPaneContext(f.services.messages, 'builtin.editor', 'lib/app.dart  ·  modified');
+    // Focus a pane with no status → the slot clears.
+    focus.setActive(slot: Slots.workspace, contributionId: 'pane.y');
     await tester.pump();
-    await tester.pump();
-    expect(find.textContaining('opus 4.7'), findsNothing);
-    expect(find.textContaining('lib/app.dart'), findsOneWidget);
-
-    // Empty clears it.
-    publishPaneContext(f.services.messages, 'builtin.editor', '');
-    await tester.pump();
-    await tester.pump();
-    expect(find.byType(ClideText), findsNothing);
+    expect(find.text('S'), findsNothing);
   });
 }

test/kernel/src/focus_test.dart

@@ -0,0 +1,54 @@
+/// Tests for FocusTracker's status-widget slot (T-150).
+library;
+
+import 'package:clide/kernel/src/focus.dart';
+import 'package:clide/kernel/src/panels/slot_id.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('FocusTracker status widget', () {
+    test('setStatusWidget applies only for the focused contribution', () {
+      final f = FocusTracker();
+      f.setActive(slot: Slots.workspace, contributionId: 'a');
+      const wa = SizedBox(key: ValueKey('a'));
+      f.setStatusWidget('a', wa);
+      expect(f.activeStatusWidget, wa);
+
+      // A background contribution's update is ignored.
+      f.setStatusWidget('b', const SizedBox(key: ValueKey('b')));
+      expect(f.activeStatusWidget, wa);
+    });
+
+    test('a focus change clears the previous status widget', () {
+      final f = FocusTracker();
+      f.setActive(slot: Slots.workspace, contributionId: 'a');
+      f.setStatusWidget('a', const SizedBox());
+      expect(f.activeStatusWidget, isNotNull);
+
+      f.setActive(slot: Slots.workspace, contributionId: 'b');
+      expect(f.activeStatusWidget, isNull);
+    });
+
+    test('clear() resets focus and status', () {
+      final f = FocusTracker();
+      f.setActive(slot: Slots.workspace, contributionId: 'a');
+      f.setStatusWidget('a', const SizedBox());
+      f.clear();
+      expect(f.activeContributionId, isNull);
+      expect(f.activeStatusWidget, isNull);
+    });
+
+    test('setStatusWidget notifies on change, not on a repeat', () {
+      final f = FocusTracker();
+      f.setActive(slot: Slots.workspace, contributionId: 'a');
+      var n = 0;
+      f.addListener(() => n++);
+      const w = SizedBox();
+      f.setStatusWidget('a', w);
+      expect(n, 1);
+      f.setStatusWidget('a', w); // identical → no notify
+      expect(n, 1);
+    });
+  });
+}

test/widgets/src/clide_marquee_test.dart

@@ -0,0 +1,32 @@
+/// Tests for ClideMarquee (T-150): static when the child fits, scrolls
+/// (looped copy) when it overflows; clips its box.
+library;
+
+import 'package:clide/widgets/widgets.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+Widget _boxed(double width, Widget child) => Directionality(
+      textDirection: TextDirection.ltr,
+      child: Center(
+        child: SizedBox(width: width, height: 16, child: child),
+      ),
+    );
+
+void main() {
+  testWidgets('shows the child statically when it fits', (tester) async {
+    await tester.pumpWidget(_boxed(300, const ClideMarquee(child: Text('short'))));
+    await tester.pump();
+    expect(find.text('short'), findsOneWidget);
+    await tester.pumpWidget(const SizedBox()); // tear down the ticker
+  });
+
+  testWidgets('renders a looped copy and runs without overflow when wider than the slot', (tester) async {
+    await tester.pumpWidget(_boxed(40, const ClideMarquee(child: Text('a long status line that overflows the slot'))));
+    await tester.pump(); // measure
+    await tester.pump(const Duration(milliseconds: 100)); // advance the ticker
+    expect(find.text('a long status line that overflows the slot'), findsWidgets);
+    expect(tester.takeException(), isNull);
+    await tester.pumpWidget(const SizedBox()); // dispose → stop ticker
+  });
+}

test/widgets/src/clide_pane_test.dart

@@ -0,0 +1,78 @@
+/// Tests for ClidePane (T-150): it surfaces its statusWidget to the
+/// FocusTracker slot only while it is the shown (focused + active) pane.
+library;
+
+import 'package:clide/kernel/src/panels/slot_id.dart';
+import 'package:clide/widgets/widgets.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../../helpers/kernel_fixture.dart';
+import '../../helpers/widget_harness.dart';
+
+void main() {
+  late KernelFixture f;
+  setUp(() async => f = await KernelFixture.create());
+  tearDown(() => f.dispose());
+
+  testWidgets('conveys its status while its contribution is focused, clears on blur', (tester) async {
+    await tester.pumpWidget(harness(
+      f,
+      const ClidePane(
+        contributionId: 'pane.x',
+        statusWidget: Text('S', textDirection: TextDirection.ltr),
+        child: SizedBox(),
+      ),
+    ));
+    final focus = f.services.focus;
+    expect(focus.activeStatusWidget, isNull); // not focused yet
+
+    focus.setActive(slot: Slots.workspace, contributionId: 'pane.x');
+    await tester.pump();
+    expect(focus.activeStatusWidget, isA<Text>());
+
+    focus.setActive(slot: Slots.workspace, contributionId: 'other');
+    await tester.pump();
+    expect(focus.activeStatusWidget, isNull); // focus moved away → cleared
+  });
+
+  testWidgets('an inactive pane never conveys', (tester) async {
+    await tester.pumpWidget(harness(
+      f,
+      const ClidePane(
+        contributionId: 'pane.x',
+        active: false,
+        statusWidget: Text('S', textDirection: TextDirection.ltr),
+        child: SizedBox(),
+      ),
+    ));
+    f.services.focus.setActive(slot: Slots.workspace, contributionId: 'pane.x');
+    await tester.pump();
+    expect(f.services.focus.activeStatusWidget, isNull);
+  });
+
+  testWidgets('re-conveys when statusWidget changes while focused', (tester) async {
+    f.services.focus.setActive(slot: Slots.workspace, contributionId: 'pane.x');
+    var label = 'A';
+    late StateSetter setLabel;
+    await tester.pumpWidget(harness(
+      f,
+      StatefulBuilder(
+        builder: (ctx, setState) {
+          setLabel = setState;
+          return ClidePane(
+            contributionId: 'pane.x',
+            statusWidget: Text(label, textDirection: TextDirection.ltr),
+            child: const SizedBox(),
+          );
+        },
+      ),
+    ));
+    await tester.pump();
+    expect((f.services.focus.activeStatusWidget! as Text).data, 'A');
+
+    setLabel(() => label = 'B');
+    await tester.pump();
+    expect((f.services.focus.activeStatusWidget! as Text).data, 'B');
+  });
+}