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>

lib/builtin/claude/src/claude_pane.dart

@@ -15,7 +15,6 @@ import 'conversation_controller.dart';
 import 'conversation_view.dart';
 import 'session_naming.dart';
 import 'tmux_session.dart' as tmux;
-import 'pane_context_status.dart';
 import 'transcript_publisher.dart';
 import 'transcript_reader.dart';
 
@@ -26,16 +25,22 @@ class ClaudePane extends StatefulWidget {
     this.secondaryIndex,
     this.showChrome = true,
     this.active = true,
+    this.contributionId = 'claude.primary',
   }) : assert(isPrimary || secondaryIndex != null, 'secondary panes need an index');
 
   final bool isPrimary;
   final bool showChrome;
   final int? secondaryIndex;
 
-  /// Whether this pane is the visible/focused tab. Only the active pane
-  /// publishes its status to the status-bar context slot (T-145).
+  /// Whether this pane is the visible/focused sub-tab. Only the active
+  /// pane publishes its status to the status-bar context slot (T-145).
   final bool active;
 
+  /// Workspace contribution id this pane lives under (the Claude tab —
+  /// keep in sync with the extension's TabContribution id). The status
+  /// slot shows our message only while this contribution is focused.
+  final String contributionId;
+
   @override
   State<ClaudePane> createState() => _ClaudePaneState();
 }
@@ -63,22 +68,18 @@ class _ClaudePaneState extends State<ClaudePane> {
   bool _spawned = false;
   bool _usingTmux = false;
 
-  // Publish this pane's status line to the status-bar context slot, but
-  // only when it's the active tab — the active pane owns the slot; an
-  // inactive pane staying quiet lets the active one win without a race
-  // (T-145). Switching tabs re-publishes from the newly-active pane.
-  void _publishContext() {
-    if (!widget.active || _status.isEmpty) return;
-    final messages = _kernel()?.messages;
-    if (messages == null) return;
-    publishPaneContext(messages, 'builtin.claude', formatStatusLine(_status));
-  }
-
-  @override
-  void didUpdateWidget(ClaudePane old) {
-    super.didUpdateWidget(old);
-    // Became the active tab → push our status into the slot.
-    if (widget.active && !old.active) _publishContext();
+  // The status line surfaced to the bottom status bar via ClidePane —
+  // null until Claude reports a model/mode/context. ClidePane conveys it
+  // while this pane is the focused one (T-150).
+  Widget? _statusWidget(SurfaceTokens tokens) {
+    if (_status.isEmpty) return null;
+    return ClideText(
+      formatStatusLine(_status),
+      fontSize: clideFontSmall,
+      fontFamily: clideMonoFamily,
+      color: tokens.statusBarForeground,
+      maxLines: 1,
+    );
   }
 
   @override
@@ -279,10 +280,11 @@ class _ClaudePaneState extends State<ClaudePane> {
       channel: channel,
     );
     _conversation = ConversationController.fromBus(messages: messages, channel: channel);
+    // On status change, rebuild — ClidePane re-conveys the new statusWidget
+    // to the bar while this pane is focused (T-150).
     _statusSub = _feed!.statusStream.listen((s) {
       if (!mounted) return;
       setState(() => _status = s);
-      _publishContext();
     });
     _subscribe();
     setState(() {});
@@ -345,6 +347,7 @@ class _ClaudePaneState extends State<ClaudePane> {
   @override
   Widget build(BuildContext context) {
     final title = widget.isPrimary ? 'claude — primary' : 'claude — secondary ${widget.secondaryIndex}';
+    final tokens = ClideTheme.of(context).surface;
 
     final Widget body;
     if (_error != null) {
@@ -376,20 +379,29 @@ class _ClaudePaneState extends State<ClaudePane> {
       body = const Center(child: ClideText('attaching…', muted: true));
     }
 
-    if (!widget.showChrome) return body;
+    final content = widget.showChrome
+        ? ClidePaneChrome(
+            title: title,
+            subtitle: _error ?? _statusLine,
+            onClose: widget.isPrimary
+                ? null
+                : () {
+                    final id = _paneId;
+                    if (id != null) {
+                      unawaited(_ipc()?.request('pane.close', args: {'id': id}));
+                    }
+                  },
+            child: body,
+          )
+        : body;
 
-    return ClidePaneChrome(
-      title: title,
-      subtitle: _error ?? _statusLine,
-      onClose: widget.isPrimary
-          ? null
-          : () {
-              final id = _paneId;
-              if (id != null) {
-                unawaited(_ipc()?.request('pane.close', args: {'id': id}));
-              }
-            },
-      child: body,
+    // Surface this pane's status to the bottom status-bar slot while it's
+    // the focused pane (T-150).
+    return ClidePane(
+      contributionId: widget.contributionId,
+      active: widget.active,
+      statusWidget: _statusWidget(tokens),
+      child: content,
     );
   }
 }

lib/builtin/claude/src/pane_context_status.dart

@@ -1,74 +1,44 @@
-/// The status-bar "in-pane context" slot (T-145).
-///
-/// A generic, publisher-agnostic slot: a pane publishes a short status
-/// string to [paneContextChannel] on the MessageBus, and the bottom
-/// status bar shows the latest one. The active pane publishes (an
-/// inactive pane stays quiet), so switching tabs swaps the slot to the
-/// newly-active pane's message. The Claude pane is the first publisher
-/// (model · permission-mode · context); other panes can use the same
-/// channel.
+/// Status-bar item that shows the *focused* pane's status widget
+/// (T-150). The content comes from whichever pane is focused — each pane
+/// surfaces its own [ClidePane.statusWidget] via [FocusTracker], so this
+/// item is generic: it just renders `focus.activeStatusWidget`, clamped
+/// to a fixed height and marquee-scrolled when it overflows. Nothing
+/// (and no space) when no focused pane has a status — so it clears on
+/// focus change.
 library;
 
-import 'dart:async';
-
 import 'package:clide/kernel/kernel.dart';
 import 'package:clide/widgets/widgets.dart';
 import 'package:flutter/widgets.dart';
 
-/// MessageBus channel for the status-bar context slot. Data: `{'text': String}`.
-const paneContextChannel = 'statusbar.context';
+/// Max width the slot occupies in the status bar before marquee kicks in.
+const double _slotMaxWidth = 360;
 
-/// Publish [text] to the context slot (empty string clears it).
-void publishPaneContext(MessageBus messages, String publisher, String text) {
-  messages.publish(publisher, paneContextChannel, {'text': text});
-}
+/// Fixed slot height — panes can render anything, but not blow up the bar.
+const double _slotHeight = 16;
 
-/// Status-bar item that shows the latest pane-context message (nothing
-/// when empty). Subscribes to the bus itself via the ambient kernel.
-class PaneContextStatusItem extends StatefulWidget {
+class PaneContextStatusItem extends StatelessWidget {
   const PaneContextStatusItem({super.key});
 
-  @override
-  State<PaneContextStatusItem> createState() => _PaneContextStatusItemState();
-}
-
-class _PaneContextStatusItemState extends State<PaneContextStatusItem> {
-  StreamSubscription<Message>? _sub;
-  String _text = '';
-  bool _subscribed = false;
-
-  @override
-  void didChangeDependencies() {
-    super.didChangeDependencies();
-    if (_subscribed) return;
-    _subscribed = true;
-    final messages = ClideKernel.of(context).messages;
-    _sub = messages.subscribe(channel: paneContextChannel).listen((m) {
-      final t = (m.data['text'] as String?) ?? '';
-      if (t == _text || !mounted) return;
-      setState(() => _text = t);
-    });
-  }
-
-  @override
-  void dispose() {
-    _sub?.cancel();
-    super.dispose();
-  }
-
   @override
   Widget build(BuildContext context) {
-    if (_text.isEmpty) return const SizedBox.shrink();
-    final tokens = ClideTheme.of(context).surface;
-    return Padding(
-      padding: const EdgeInsets.symmetric(horizontal: 8),
-      child: ClideText(
-        _text,
-        fontSize: clideFontSmall,
-        fontFamily: clideMonoFamily,
-        color: tokens.statusBarForeground,
-        maxLines: 1,
-      ),
+    final focus = ClideKernel.of(context).focus;
+    return ListenableBuilder(
+      listenable: focus,
+      builder: (ctx, _) {
+        final widget = focus.activeStatusWidget;
+        if (widget == null) return const SizedBox.shrink();
+        return Padding(
+          padding: const EdgeInsets.symmetric(horizontal: 8),
+          child: SizedBox(
+            height: _slotHeight,
+            child: ConstrainedBox(
+              constraints: const BoxConstraints(maxWidth: _slotMaxWidth),
+              child: ClideMarquee(child: widget),
+            ),
+          ),
+        );
+      },
     );
   }
 }