fix(tmux): stop nested prefix keys and TUI Alt+digits from moving other clients

Docker and owned-remote tmux servers kept the stock prefix table, so Ctrl+Q
then )/(/s/w/L switch-client'd the inner client onto a sibling. Those create
chains now leave only C-q send-prefix.

codeman tui bound M-1..M-9 in the server-wide root table. The keys stay, but
switch-client runs only for the attaching client (tty plus a one-shot pid).
A browser tab's Esc-then-digit no longer jumps sessions, and a killed TUI
leaves a binding that matches no live client.

Co-authored-by: DDT <1786035110@qq.com>

test/docker-exec-options.test.ts

@@ -106,6 +106,12 @@ describe('buildDockerLaunchCommand', () => {
     expect(cmd).toContain('tmux -L codeman-docker setenv -g CODEMAN_SESSION_ID');
     expect(cmd).toContain('new-session -A -s codeman-dkr-1a2b3c4d');
     expect(cmd).toContain("sh -lc '");
+    // The in-container tmux keeps prefix C-q. Without this reduction its stock
+    // prefix table runs switch-client / choose-tree for the inner client.
+    const unbind = cmd.indexOf('unbind-key -a -T prefix');
+    const bind = cmd.indexOf('bind-key -T prefix C-q send-prefix');
+    expect(unbind).toBeGreaterThan(cmd.indexOf('prefix C-q'));
+    expect(bind).toBeGreaterThan(unbind);
   });
 
   it('pins a deterministic conversation id with a reboot-surviving fallback (fresh launch)', () => {

test/remote-ssh-options.test.ts

@@ -164,6 +164,12 @@ describe('COD-107 buildRemoteLaunchCommand — threads connection args', () => {
       'set -s escape-time 0',
       // COD-106 — shared/collaborative sizing, per-session scoped (never -g).
       `set -t ${remoteName} window-size latest`,
+      // #671 — the nested server's prefix table is stock unless this chain
+      // reduces it. Ctrl+Q then ) would switch-client onto a sibling session.
+      // Before remain-on-exit: a remote tmux that rejects `failed` aborts the
+      // rest of the chain, and that option has to stay last.
+      'unbind-key -a -T prefix',
+      'bind-key -T prefix C-q send-prefix',
       // #210 — keep a CRASHED pane for diagnosis. `failed` (not `on`, which would
       // also strand a pane after a clean `exit`), and LAST because tmux aborts the
       // remaining commands of a `\;` chain on error and `failed` needs tmux >= 3.2.

test/tmux-prefix-table.test.ts

@@ -15,7 +15,11 @@ import { afterAll, beforeAll, describe, expect, it } from 'vitest';
 import { execSync } from 'node:child_process';
 import { rmSync } from 'node:fs';
 import * as pty from 'node-pty';
-import { prefixTableNeedsReset, restrictTmuxPrefixTable } from '../src/tmux-prefix-table.js';
+import {
+  nestedPrefixTableResetCommands,
+  prefixTableNeedsReset,
+  restrictTmuxPrefixTable,
+} from '../src/tmux-prefix-table.js';
 
 /** A trimmed copy of tmux 3.4's stock prefix table, as `list-keys -T prefix` prints it. */
 const STOCK = [
@@ -278,3 +282,84 @@ describe.skipIf(!hasTmux)('restrictTmuxPrefixTable against a real tmux (private
     }
   });
 });
+
+describe.skipIf(!hasTmux)('nested Docker/remote tmux prefix table (private socket)', () => {
+  // What buildRemoteLaunchCommand / buildDockerLaunchCommand create: prefix C-q
+  // on a dedicated server, then the two commands nestedPrefixTableResetCommands
+  // emits. The inner client is the docker-exec / ssh process; Ctrl+Q is its prefix.
+  const socket = `codeman-nested-prefix-${process.pid}`;
+  const tmux = `tmux -L ${socket} -f /dev/null`;
+  const run = (cmd: string): string => execSync(cmd, { encoding: 'utf8', stdio: ['ignore', 'pipe', 'ignore'] });
+  let client: pty.IPty | null = null;
+
+  const clientSession = () => run(`${tmux} list-clients -F '#{client_session}'`).trim();
+
+  async function waitFor(check: () => boolean, ms = 3000): Promise<boolean> {
+    const deadline = Date.now() + ms;
+    while (Date.now() < deadline) {
+      if (check()) return true;
+      await new Promise((resolve) => setTimeout(resolve, 50));
+    }
+    return check();
+  }
+
+  beforeAll(async () => {
+    // `stty -ixon` in the pane so a delivered C-q is visible to cat -v as ^Q
+    // instead of being eaten as XON. The attach client below is what must also
+    // deliver C-q; node-pty opens the pty raw, which clears IXON on that side.
+    run(`${tmux} new-session -d -s alpha -x 80 -y 24 'stty -ixon; cat -v'`);
+    run(`${tmux} new-session -d -s beta -x 80 -y 24 'stty -ixon; cat -v'`);
+    run(`${tmux} set-option -t alpha prefix C-q`);
+    run(`${tmux} set-option -t beta prefix C-q`);
+    const env = { ...process.env } as Record<string, string>;
+    delete env.TMUX;
+    client = pty.spawn('tmux', ['-L', socket, '-f', '/dev/null', 'attach-session', '-t', 'alpha'], {
+      name: 'xterm-256color',
+      cols: 80,
+      rows: 24,
+      env,
+    });
+    expect(await waitFor(() => clientSession() === 'alpha')).toBe(true);
+  });
+
+  afterAll(() => {
+    client?.kill();
+    let socketPath = '';
+    try {
+      socketPath = run(`${tmux} display-message -p '#{socket_path}'`).trim();
+      run(`${tmux} kill-server`);
+    } catch {
+      /* already gone */
+    }
+    if (socketPath.endsWith(`/${socket}`)) rmSync(socketPath, { force: true });
+  });
+
+  it('with the stock table, Ctrl+Q ) moves the inner client onto the other session', async () => {
+    client!.write('\x11)');
+    expect(await waitFor(() => clientSession() === 'beta')).toBe(true);
+    const name = run(`${tmux} list-clients -F '#{client_name}'`).trim();
+    run(`${tmux} switch-client -c ${name} -t alpha`);
+    expect(await waitFor(() => clientSession() === 'alpha')).toBe(true);
+  });
+
+  it('after the nested reset, Ctrl+Q ), s and w leave the client, and Ctrl+Q Ctrl+Q reaches the pane', async () => {
+    for (const command of nestedPrefixTableResetCommands()) run(`${tmux} ${command}`);
+
+    const prefix = run(`${tmux} list-keys -T prefix`)
+      .split('\n')
+      .filter((line) => line.trim());
+    expect(prefix).toEqual([expect.stringMatching(/-T prefix C-q\s+send-prefix$/)]);
+
+    client!.write('\x11)');
+    await new Promise((resolve) => setTimeout(resolve, 300));
+    client!.write('\x11s');
+    await new Promise((resolve) => setTimeout(resolve, 300));
+    client!.write('\x11w');
+    await new Promise((resolve) => setTimeout(resolve, 300));
+    expect(clientSession()).toBe('alpha');
+    expect(run(`${tmux} display-message -p -t alpha '#{pane_in_mode}'`).trim()).toBe('0');
+
+    client!.write('\x11\x11');
+    expect(await waitFor(() => run(`${tmux} capture-pane -p -t alpha`).includes('^Q'))).toBe(true);
+  });
+});

test/tui/tui-app.test.ts

@@ -626,12 +626,90 @@ describe('the way out when F1 is taken, on a socket with no detach key', () => {
       restoreWindowSizing: async () => true,
     } as unknown as TuiClient;
 
-    const handoff = await beginAttachHandoff(client, 'codeman-abc12345', 'w1-case');
+    const handoff = await beginAttachHandoff(client, 'codeman-abc12345', 'w1-case', [], undefined, undefined, null);
 
     expect(handoff.chord).toBe('Ctrl+B then Ctrl+D');
   });
 });
 
+describe('attach switch keys stay on the TUI client', () => {
+  it('binds M-1 through the guard for the tty it was given, and does not bind without one', async () => {
+    const binds: Array<{ key: string; target: string; tty: string }> = [];
+    const unbinds: Array<{ key: string; owner: string | undefined }> = [];
+    let armed: string | null = null;
+    let disarmed: string | null = null;
+    const client = {
+      readPrefixKey: async () => 'C-b',
+      readDetachKey: async () => 'd',
+      readPrefixBinding: async () => null,
+      bindDetachKey: async () => true,
+      unbindDetachKey: async () => true,
+      armTuiSwitchGuard: async (tty: string) => {
+        armed = tty;
+        return true;
+      },
+      disarmTuiSwitchGuard: async (tty: string) => {
+        disarmed = tty;
+      },
+      bindSwitchKey: async (key: string, target: string, tty: string) => {
+        binds.push({ key, target, tty });
+        return true;
+      },
+      unbindSwitchKey: async (key: string, owner?: string) => {
+        unbinds.push({ key, owner });
+      },
+      readSessionOptions: async () => null,
+      applySessionOptions: async () => true,
+      restoreSessionOptions: async () => true,
+      readWindowSizing: async () => null,
+      presizeWindow: async () => true,
+      followAttachingClient: async () => true,
+      restoreWindowSizing: async () => true,
+    } as unknown as TuiClient;
+
+    const tabs = [
+      { index: 1, label: 'w1', active: true, muxName: 'codeman-aaaa1111' },
+      { index: 2, label: 'w2', active: false, muxName: 'codeman-bbbb2222' },
+    ];
+    const handoff = await beginAttachHandoff(
+      client,
+      'codeman-aaaa1111',
+      'w1',
+      tabs,
+      undefined,
+      undefined,
+      '/dev/pts/4'
+    );
+    expect(armed).toBe('/dev/pts/4');
+    expect(binds).toEqual([
+      { key: 'M-1', target: 'codeman-aaaa1111', tty: '/dev/pts/4' },
+      { key: 'M-2', target: 'codeman-bbbb2222', tty: '/dev/pts/4' },
+    ]);
+    // Takeover clears M-1..M-9 before claiming, so a killed TUI's leftovers go.
+    expect(unbinds.filter((entry) => entry.owner === undefined).map((entry) => entry.key)).toEqual([
+      'M-1',
+      'M-2',
+      'M-3',
+      'M-4',
+      'M-5',
+      'M-6',
+      'M-7',
+      'M-8',
+      'M-9',
+    ]);
+
+    await handoff.restore();
+    expect(disarmed).toBe('/dev/pts/4');
+    expect(unbinds.filter((entry) => entry.owner === '/dev/pts/4').map((entry) => entry.key)).toEqual(['M-1', 'M-2']);
+
+    binds.length = 0;
+    armed = null;
+    await beginAttachHandoff(client, 'codeman-aaaa1111', 'w1', tabs, undefined, undefined, null);
+    expect(armed).toBeNull();
+    expect(binds).toEqual([]);
+  });
+});
+
 describe('naming a session the TUI starts', () => {
   it("follows the web UI's w<n>-<case> convention", () => {
     expect(nextSessionName('mirofish', [])).toBe('w1-mirofish');

test/tui/tui-client.test.ts

@@ -25,6 +25,11 @@ import {
   parseSessionOptions,
   parseDetachKey,
   parsePrefixBinding,
+  isTuiSwitchBinding,
+  tuiSwitchBindingTty,
+  tuiSwitchAttachHook,
+  tuiSwitchGuard,
+  isTuiClientTty,
   ATTACH_BANNER_MARKER,
   parseTmuxSessionList,
   parseWindowSizing,
@@ -619,31 +624,73 @@ describe('attach window sizing', () => {
 });
 
 describe('TuiClient.bindSwitchKey', () => {
-  it('escapes the command separator, or tmux runs the second command instead of binding it', () => {
+  it('guards switch-client to one client tty, and keeps both commands inside the if-shell string', () => {
     // ⚠️ A bare `;` argument is a command separator to tmux's OWN parser: it
-    // ends the bind-key and executes what follows immediately. That bound only
-    // `switch-client` and ran `window-size latest` against every session at
-    // attach time, which is why sessions were left on `latest` after a detach —
-    // the sizing snapshot was taken from already-corrupted state. Verified
-    // against real tmux both ways before this test was written.
+    // ends the bind-key and executes what follows immediately. The two commands
+    // therefore live in the single if-shell argument, where `;` separates them
+    // when the key fires rather than when the key is bound. An unscoped
+    // `switch-client` is refused: key tables are server-wide, and that binding
+    // would move a browser tab on Esc then a digit.
     const calls: string[][] = [];
     const exec: TuiExecFile = async (_file, args) => {
       calls.push([...args]);
       return { stdout: '', stderr: '' };
     };
     const client = new TuiClient({ baseUrl, socket: 'codeman-beta', exec });
-    return client.bindSwitchKey('M-2', 'codeman-aaaa1111').then(() => {
+    return client.bindSwitchKey('M-2', 'codeman-aaaa1111', '/dev/pts/4').then(async () => {
       const bind = calls.find((args) => args.includes('bind-key'));
       expect(bind).toBeDefined();
-      expect(bind).toContain('\\;');
       expect(bind).not.toContain(';');
-      // Both commands have to be in the ONE binding.
-      expect(bind?.join(' ')).toContain('switch-client -t codeman-aaaa1111');
-      expect(bind?.join(' ')).toContain('window-size latest');
+      expect(bind).not.toContain('\\;');
+      const command = bind?.at(-1) ?? '';
+      expect(command).toContain(
+        'switch-client -t codeman-aaaa1111 ; set-window-option -t codeman-aaaa1111 window-size latest'
+      );
+      expect(bind).toContain('if-shell');
+      expect(bind).toContain('-F');
+      expect(bind?.join(' ')).toContain('#{client_tty},/dev/pts/4');
+      expect(bind?.join(' ')).toContain('#{@codeman-tui-pid}');
+      expect(await client.bindSwitchKey('M-2', 'codeman-aaaa1111', '/tmp/not-a-tty')).toBe(false);
+      expect(await client.bindSwitchKey('M-2', 'other-session', '/dev/pts/4')).toBe(false);
     });
   });
 });
 
+describe('TUI switch-key guard', () => {
+  const guarded =
+    'if-shell -F "#{&&:#{==:#{client_tty},/dev/pts/4},#{==:#{client_pid},#{@codeman-tui-pid}}}" "switch-client -t codeman-aaaa1111 ; set-window-option -t codeman-aaaa1111 window-size latest"';
+
+  it('recognises our binding and the legacy unscoped one, and leaves a user binding alone', () => {
+    expect(isTuiSwitchBinding(guarded)).toBe(true);
+    expect(tuiSwitchBindingTty(guarded)).toBe('/dev/pts/4');
+    expect(
+      isTuiSwitchBinding(
+        'switch-client -t codeman-aaaa1111 \\; set-window-option -t codeman-aaaa1111 window-size latest'
+      )
+    ).toBe(true);
+    expect(isTuiSwitchBinding('switch-client -t codeman-aaaa1111')).toBe(true);
+    expect(tuiSwitchBindingTty('switch-client -t codeman-aaaa1111')).toBeNull();
+    expect(isTuiSwitchBinding('switch-client -n')).toBe(false);
+    expect(isTuiSwitchBinding('switch-client -t my-session')).toBe(false);
+    expect(isTuiSwitchBinding('display-message mine')).toBe(false);
+  });
+
+  it('refuses a tty that is not safe to interpolate, and defers client_pid in the hook', () => {
+    expect(isTuiClientTty('/dev/pts/4')).toBe(true);
+    expect(isTuiClientTty('/dev/ttys003')).toBe(true);
+    expect(isTuiClientTty('/tmp/pty')).toBe(false);
+    expect(isTuiClientTty('/dev/pts/4; rm')).toBe(false);
+    expect(tuiSwitchGuard('/dev/pts/4')).toContain('#{client_tty},/dev/pts/4');
+    expect(tuiSwitchGuard('/dev/pts/4')).toContain('#{@codeman-tui-pid}');
+    // A bare #{client_pid} is expanded when the hook is stored, with no client
+    // attached, and the pid is then empty forever. The backslash defers it.
+    const hook = tuiSwitchAttachHook('/dev/pts/4');
+    expect(hook).toContain('/dev/pts/4');
+    expect(hook).toContain('\\#{client_pid}');
+    expect(hook).toContain('set-hook -gu client-attached[90]');
+  });
+});
+
 describe('parsePrefixBinding', () => {
   const REAL = [
     'bind-key    -T prefix d       detach-client',

test/tui/tui-switch-guard.test.ts

@@ -0,0 +1,214 @@
+/**
+ * @fileoverview Alt+1..9 on a `codeman tui` attach must not move any other tmux
+ * client. Key tables are server-wide, so the binding exists for every client;
+ * the command runs only for the TUI's own tty and pid.
+ *
+ * Against a real tmux on a private socket (never Codeman's). One client is
+ * attached on a pty whose tty is known BEFORE `tmux attach` runs, which is how
+ * the TUI arms the hook. A second client is what a browser tab is.
+ *
+ * Port: N/A (no server)
+ */
+import { afterAll, describe, expect, it } from 'vitest';
+import { execFileSync, execSync, spawn, type ChildProcess } from 'node:child_process';
+import { readlinkSync, rmSync } from 'node:fs';
+import { createInterface } from 'node:readline';
+import * as pty from 'node-pty';
+import { TuiClient } from '../../src/tui/tui-client.js';
+
+const hasTmux = (() => {
+  try {
+    execSync('tmux -V', { stdio: 'ignore' });
+    execSync('python3 -c "import pty"', { stdio: 'ignore' });
+    return true;
+  } catch {
+    return false;
+  }
+})();
+
+/**
+ * Holds a pty open, prints its tty, and execs `tmux attach` on that slave only
+ * after stdin says GO. IXON is off so a byte is never swallowed as flow control.
+ */
+const PTY_HELPER = `
+import os, pty, sys, termios, signal
+socket, session = sys.argv[1], sys.argv[2]
+master, slave = pty.openpty()
+attr = termios.tcgetattr(slave)
+attr[0] &= ~(termios.IXON | termios.IXOFF)
+termios.tcsetattr(slave, termios.TCSANOW, attr)
+sys.stdout.write(os.ttyname(slave) + "\\n")
+sys.stdout.flush()
+if not sys.stdin.readline().startswith("GO"):
+    sys.exit(1)
+env = os.environ.copy()
+env["TERM"] = "xterm-256color"
+env.pop("TMUX", None)
+pid = os.fork()
+if pid == 0:
+    os.setsid()
+    os.dup2(slave, 0)
+    os.dup2(slave, 1)
+    os.dup2(slave, 2)
+    os.close(master)
+    os.close(slave)
+    os.execvpe("tmux", ["tmux", "-f", "/dev/null", "-L", socket, "attach-session", "-t", session], env)
+os.close(slave)
+sys.stdout.write("ATTACHED\\n")
+sys.stdout.flush()
+while True:
+    line = sys.stdin.readline()
+    if not line or line.startswith("EXIT"):
+        break
+    if line.startswith("KEY "):
+        os.write(master, bytes.fromhex(line[4:].strip()))
+os.kill(pid, signal.SIGTERM)
+try:
+    os.waitpid(pid, 0)
+except ChildProcessError:
+    pass
+os.close(master)
+`;
+
+describe.skipIf(!hasTmux)('TUI M-1..M-9 switch only the attaching client', () => {
+  const socket = `codeman-tui-switch-${process.pid}`;
+  const alpha = 'codeman-aaaa1111';
+  const beta = 'codeman-bbbb2222';
+  const run = (args: readonly string[]): string =>
+    execFileSync('tmux', ['-L', socket, '-f', '/dev/null', ...args], {
+      encoding: 'utf8',
+      stdio: ['ignore', 'pipe', 'pipe'],
+    });
+  const client = new TuiClient({ socket });
+  let helper: ChildProcess | null = null;
+  let other: pty.IPty | null = null;
+  const lines: string[] = [];
+  let waiters: Array<(line: string) => void> = [];
+
+  function pushLine(line: string): void {
+    const waiter = waiters.shift();
+    if (waiter) waiter(line);
+    else lines.push(line);
+  }
+
+  function nextLine(): Promise<string> {
+    const queued = lines.shift();
+    if (queued !== undefined) return Promise.resolve(queued);
+    return new Promise((resolve) => waiters.push(resolve));
+  }
+
+  function sessions(): Map<string, { session: string; pid: string }> {
+    let out = '';
+    try {
+      out = run(['list-clients', '-F', '#{client_tty}\t#{client_session}\t#{client_pid}']);
+    } catch {
+      return new Map();
+    }
+    const map = new Map<string, { session: string; pid: string }>();
+    for (const line of out.split('\n')) {
+      const [tty, session, pid] = line.trim().split('\t');
+      if (tty && session) map.set(tty, { session, pid: pid ?? '' });
+    }
+    return map;
+  }
+
+  async function waitFor(check: () => boolean, ms = 4000): Promise<boolean> {
+    const deadline = Date.now() + ms;
+    while (Date.now() < deadline) {
+      if (check()) return true;
+      await new Promise((resolve) => setTimeout(resolve, 40));
+    }
+    return check();
+  }
+
+  afterAll(() => {
+    try {
+      helper?.stdin?.write('EXIT\n');
+    } catch {
+      /* helper already gone */
+    }
+    helper?.kill();
+    other?.kill();
+    let socketPath = '';
+    try {
+      socketPath = run(['display-message', '-p', '#{socket_path}']).trim();
+      run(['kill-server']);
+    } catch {
+      /* already gone */
+    }
+    if (socketPath.endsWith(`/${socket}`)) rmSync(socketPath, { force: true });
+  });
+
+  it('switches the armed client only, including after that client has died', async () => {
+    run(['new-session', '-d', '-s', alpha, '-x', '80', '-y', '24', 'sleep 300']);
+    run(['new-session', '-d', '-s', beta, '-x', '80', '-y', '24', 'sleep 300']);
+
+    helper = spawn('python3', ['-c', PTY_HELPER, socket, alpha], { stdio: ['pipe', 'pipe', 'inherit'] });
+    createInterface({ input: helper.stdout! }).on('line', pushLine);
+    const tty = (await nextLine()).trim();
+    expect(tty).toMatch(/^\/dev\/pts\/[0-9]+$/);
+
+    expect(await client.armTuiSwitchGuard(tty)).toBe(true);
+    const hooks = run(['show-hooks', '-g']);
+    expect(hooks).toContain('client-attached[90]');
+    expect(hooks).toContain(tty);
+    // Expanded at set-hook time this is empty and the guard never matches.
+    expect(hooks).toContain('#{client_pid}');
+
+    helper.stdin!.write('GO\n');
+    expect(await nextLine()).toBe('ATTACHED');
+    expect(await waitFor(() => sessions().get(tty)?.session === alpha)).toBe(true);
+
+    const pid = sessions().get(tty)?.pid ?? '';
+    expect(pid).toMatch(/^[0-9]+$/);
+    expect(await waitFor(() => run(['show-options', '-gv', '@codeman-tui-pid']).trim() === pid)).toBe(true);
+    // One-shot: a later client on a reused pty is not recorded.
+    expect(run(['show-hooks', '-g'])).not.toContain('client-attached[90]');
+
+    expect(await client.bindSwitchKey('M-2', 'not-a-codeman-session', tty)).toBe(false);
+    expect(await client.bindSwitchKey('M-2', beta, '/tmp/not-a-tty')).toBe(false);
+    expect(await client.bindSwitchKey('M-2', beta, tty)).toBe(true);
+    const listed = run(['list-keys', '-T', 'root']);
+    expect(listed).toContain('if-shell -F');
+    expect(listed).toContain(tty);
+    expect(listed).toContain(`switch-client -t ${beta}`);
+
+    // Esc then 2, one write, inside escape-time: tmux reads it as M-2.
+    helper.stdin!.write('KEY 1b32\n');
+    expect(await waitFor(() => sessions().get(tty)?.session === beta)).toBe(true);
+
+    const env = { ...process.env } as Record<string, string>;
+    delete env.TMUX;
+    other = pty.spawn('tmux', ['-L', socket, '-f', '/dev/null', 'attach-session', '-t', alpha], {
+      name: 'xterm-256color',
+      cols: 80,
+      rows: 24,
+      env,
+    });
+    const otherTty = readlinkSync(`/proc/${other.pid}/fd/0`);
+    expect(otherTty).not.toBe(tty);
+    expect(await waitFor(() => sessions().get(otherTty)?.session === alpha)).toBe(true);
+
+    other.write('\x1b2');
+    await new Promise((resolve) => setTimeout(resolve, 400));
+    expect(sessions().get(otherTty)?.session).toBe(alpha);
+    expect(sessions().get(tty)?.session).toBe(beta);
+
+    // Killed before restore(): the binding remains, the pid is the dead client.
+    helper.stdin!.write('EXIT\n');
+    helper = null;
+    expect(await waitFor(() => !sessions().has(tty))).toBe(true);
+    expect(run(['list-keys', '-T', 'root'])).toContain(`#{client_tty},${tty}`);
+    expect(run(['show-options', '-gv', '@codeman-tui-pid']).trim()).toBe(pid);
+
+    other.write('\x1b2');
+    await new Promise((resolve) => setTimeout(resolve, 400));
+    expect(sessions().get(otherTty)?.session).toBe(alpha);
+
+    // restore() drops the key because it still names this tty, and the dead pid.
+    await client.unbindSwitchKey('M-2', tty);
+    await client.disarmTuiSwitchGuard(tty);
+    expect(run(['list-keys', '-T', 'root'])).not.toContain(`switch-client -t ${beta}`);
+    expect(() => run(['show-options', '-gv', '@codeman-tui-pid'])).toThrow();
+  });
+});