kill secondary Claude tmux sessions on tab close (T-87)

Adds lib/builtin/claude/src/tmux_session.dart with helpers for the
clide-socket tmux server: killSession, listClideSessions,
reapSecondaries, killAllForRepo. The runner is overrideable via a
TmuxRunner typedef so tests don't shell out for real.

Wires ClaudePane.dispose() to call killSession(sessionName) for
secondary panes. Primary panes are left alone — D-41 keeps the
primary's tmux session alive across clide restarts so the next
launch re-attaches via `tmux new-session -A`.

Imports the helpers in the Claude extension as groundwork for the
app-shutdown reap and the existing claude.kill-all-sessions
command — wiring those uses lands separately.

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

.pql/pql-plan.json

@@ -1,5 +1,5 @@
 {
-  "exported_at": "2026-05-06T14:40:38Z",
+  "exported_at": "2026-05-06T14:41:33Z",
   "decisions": [
     {
       "id": "D-1",

CHANGELOG.md

@@ -48,6 +48,10 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Fixed
 
+- Closing a secondary Claude pane tab now kills its tmux session
+  on the clide socket, honouring D-41's "closing a secondary kills
+  that tmux session" lifecycle. Previously `pane.close` only killed
+  the ptyc-spawned tmux client and the server-side session leaked.
 - Terminal cell grid no longer drifts on bold text — bold rendering
   is suppressed at the painter level since synthetic bold (with no
   Bold.ttf registered) shifts glyph advance widths.

lib/builtin/claude/src/claude_pane.dart

@@ -10,6 +10,7 @@ import 'package:flutter/widgets.dart';
 import 'package:clide/src/terminal/terminal.dart';
 
 import 'session_naming.dart';
+import 'tmux_session.dart' as tmux;
 
 class ClaudePane extends StatefulWidget {
   const ClaudePane({
@@ -57,12 +58,20 @@ class _ClaudePaneState extends State<ClaudePane> {
     _eventSub?.cancel();
     _eventSub = null;
     final id = _paneId;
+    final sessionName = _sessionName;
     _paneId = null;
     // Secondary panes own their tmux session — close on dispose.
     // Primary panes leave the tmux session alive so the next launch
-    // re-attaches via `tmux new-session -A` (D-041).
+    // re-attaches via `tmux new-session -A` (D-41).
+    //
+    // pane.close kills the ptyc-spawned tmux *client*; the tmux server
+    // keeps the session alive. We need an explicit kill-session for
+    // secondaries to actually disappear (D-41 close semantics).
     if (id != null && !widget.isPrimary) {
       unawaited(_ipc()?.request('pane.close', args: {'id': id}));
+      if (sessionName != null) {
+        unawaited(tmux.killSession(sessionName));
+      }
     }
     super.dispose();
   }

lib/builtin/claude/src/extension.dart

@@ -1,5 +1,7 @@
 import 'package:clide/clide.dart';
 import 'package:clide/builtin/claude/src/claude_session_host.dart';
+import 'package:clide/builtin/claude/src/session_naming.dart';
+import 'package:clide/builtin/claude/src/tmux_session.dart' as tmux;
 import 'package:clide/extension/extension.dart';
 import 'package:clide/kernel/kernel.dart';
 import 'package:flutter/widgets.dart';

lib/builtin/claude/src/tmux_session.dart

@@ -0,0 +1,61 @@
+/// tmux server interactions for Claude panes (D-41 lifecycle).
+///
+/// `pane.close` only kills the ptyc-spawned tmux *client*; tmux is
+/// client/server, so the server-side session keeps running after the
+/// client disconnects. To honour D-41 ("closing a secondary kills that
+/// tmux session" + "secondary numbering resets between clide runs"),
+/// we need explicit `tmux kill-session` calls — that's what lives here.
+library;
+
+import 'dart:io';
+
+/// Override-able runner so tests don't shell out for real.
+typedef TmuxRunner = Future<ProcessResult> Function(List<String> args);
+
+TmuxRunner tmuxRunner = _defaultRunner;
+
+Future<ProcessResult> _defaultRunner(List<String> args) =>
+    Process.run('tmux', args);
+
+const _socket = ['-L', 'clide'];
+
+/// Kill the named tmux session on the clide socket. No-op if the
+/// session does not exist (kill-session exits non-zero — we ignore it).
+Future<void> killSession(String name) async {
+  await tmuxRunner([..._socket, 'kill-session', '-t', name]);
+}
+
+/// Return the names of all sessions currently alive on the clide
+/// socket. Empty list if the server is not running.
+Future<List<String>> listClideSessions() async {
+  final r = await tmuxRunner([..._socket, 'list-sessions', '-F', '#{session_name}']);
+  if (r.exitCode != 0) return const [];
+  return (r.stdout as String)
+      .split('\n')
+      .map((s) => s.trim())
+      .where((s) => s.isNotEmpty)
+      .toList();
+}
+
+/// Kill every secondary clide-claude session whose name begins with
+/// [primaryName] and ends with `-<digits>`. Leaves the primary itself
+/// alive (D-41).
+Future<void> reapSecondaries(String primaryName) async {
+  final pattern = RegExp('^${RegExp.escape(primaryName)}-\\d+\$');
+  for (final s in await listClideSessions()) {
+    if (pattern.hasMatch(s)) {
+      await killSession(s);
+    }
+  }
+}
+
+/// Kill every clide-claude session for [primaryName], including the
+/// primary itself. Used by the explicit `claude.kill-all-sessions`
+/// command when the user wants a hard reset.
+Future<void> killAllForRepo(String primaryName) async {
+  for (final s in await listClideSessions()) {
+    if (s == primaryName || s.startsWith('$primaryName-')) {
+      await killSession(s);
+    }
+  }
+}