fix(tmux): keep browser keys from switching a tab onto another session (#669)

Squash of PR #669. Browser terminals could be moved onto another session
by tmux's prefix keys: Ctrl+B then ), (, s or w switched the tab's tmux
client to a different session while the tab kept the original's name.
Codeman's tmux socket now keeps only Ctrl+B Ctrl+B (send-prefix) in its
prefix table, and codeman tui and scripts/tmux-manager.sh get F1 as their
way out instead of Ctrl+B d.

Merge-time fixes by the maintainer: on an empty prefix table the
unbind-key that fails no longer skips binding send-prefix; a key tmux lists
escaped (prefix C-\ shows as C-\\) compares equal, so the reset does not rerun on every create;
and reconcileSessions() reduces the table at boot when the socket has live
sessions, so sessions that survive an upgrade are covered too.

Co-authored-by: christianhaberl <116439789+christianhaberl@users.noreply.github.com>
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/tmux-manager.test.ts

@@ -727,20 +727,99 @@ describe('TmuxManager (unit)', () => {
     });
   });
 
-  describe('tmux launch cwd hardening', () => {
-    async function importWithTmuxCommandsEnabled(): Promise<typeof TmuxManager> {
-      const originalVitest = process.env.VITEST;
-      vi.resetModules();
+  async function importWithTmuxCommandsEnabled(): Promise<typeof TmuxManager> {
+    const originalVitest = process.env.VITEST;
+    vi.resetModules();
+    delete process.env.VITEST;
+    const module = await import('../src/tmux-manager.js');
+    if (originalVitest === undefined) {
       delete process.env.VITEST;
-      const module = await import('../src/tmux-manager.js');
-      if (originalVitest === undefined) {
-        delete process.env.VITEST;
-      } else {
-        process.env.VITEST = originalVitest;
+    } else {
+      process.env.VITEST = originalVitest;
+    }
+    return module.TmuxManager;
+  }
+
+  describe('prefix table on the codeman socket', () => {
+    it("reduces the socket's prefix table to send-prefix before the agent starts", async () => {
+      // Browser keystrokes reach the attach client; with the stock table Ctrl+B ) or s
+      // would move a tab onto another session (the behavior itself: tmux-prefix-table.test.ts).
+      mockedExecSync.mockImplementation((cmd: string) => {
+        if (typeof cmd === 'string' && cmd.includes('which tmux')) return '/usr/bin/tmux\n';
+        if (typeof cmd === 'string' && cmd.includes('display-message') && cmd.includes('#{pane_pid}')) return '4242\n';
+        // Not tmux's stock C-b, so a hardcoded prefix cannot pass for the one read from tmux.
+        if (typeof cmd === 'string' && cmd.includes(' show-options -gv prefix')) return 'C-a\n';
+        if (typeof cmd === 'string' && cmd.includes(' list-keys -T prefix')) {
+          return 'bind-key    -T prefix C-a send-prefix\nbind-key    -T prefix ) switch-client -n\n';
+        }
+        return '';
+      });
+      const NonTestTmuxManager = await importWithTmuxCommandsEnabled();
+      const nonTestManager = new NonTestTmuxManager();
+
+      try {
+        await nonTestManager.createSession({
+          sessionId: 'abc12345-1234-5678-90ab-cdef12345678',
+          workingDir: '/project',
+          mode: 'shell',
+        });
+        const commands = mockedExecSync.mock.calls.map(([cmd]) => String(cmd));
+        expect(commands).toContain(`tmux -L 'codeman' unbind-key -a -T prefix`);
+        const bind = commands.indexOf(`tmux -L 'codeman' bind-key -T prefix 'C-a' send-prefix`);
+        expect(bind).toBeGreaterThan(commands.indexOf(`tmux -L 'codeman' unbind-key -a -T prefix`));
+        expect(bind).toBeLessThan(commands.findIndex((c) => c.includes(' respawn-pane ')));
+      } finally {
+        nonTestManager.destroy();
       }
-      return module.TmuxManager;
+    });
+
+    /** execSync for a boot-time reconcile: `panes` is what `list-panes -a` prints. */
+    function mockReconcileTmux(panes: string): void {
+      mockedExecSync.mockImplementation((cmd: string) => {
+        if (typeof cmd === 'string' && cmd.includes('which tmux')) return '/usr/bin/tmux\n';
+        if (typeof cmd === 'string' && cmd.includes(' list-panes -a ')) return panes;
+        if (typeof cmd === 'string' && cmd.includes(' show-options -gv prefix')) return 'C-a\n';
+        if (typeof cmd === 'string' && cmd.includes(' list-keys -T prefix')) {
+          return 'bind-key    -T prefix C-a send-prefix\nbind-key    -T prefix ) switch-client -n\n';
+        }
+        return '';
+      });
     }
 
+    it('reduces it at boot too, for sessions that survived an upgrade', async () => {
+      mockReconcileTmux('codeman-abc12345|4242|0||\n');
+      const NonTestTmuxManager = await importWithTmuxCommandsEnabled();
+      const nonTestManager = new NonTestTmuxManager();
+
+      try {
+        await nonTestManager.reconcileSessions();
+        const commands = mockedExecSync.mock.calls.map(([cmd]) => String(cmd));
+        const unbind = commands.indexOf(`tmux -L 'codeman' unbind-key -a -T prefix`);
+        expect(unbind).toBeGreaterThan(-1);
+        expect(commands.indexOf(`tmux -L 'codeman' bind-key -T prefix 'C-a' send-prefix`)).toBeGreaterThan(unbind);
+      } finally {
+        nonTestManager.destroy();
+      }
+    });
+
+    it('leaves the key tables alone at boot when the socket lists no pane', async () => {
+      // On an empty socket `list-keys` would start a throwaway tmux server.
+      mockReconcileTmux('');
+      const NonTestTmuxManager = await importWithTmuxCommandsEnabled();
+      const nonTestManager = new NonTestTmuxManager();
+
+      try {
+        await nonTestManager.reconcileSessions();
+        const commands = mockedExecSync.mock.calls.map(([cmd]) => String(cmd));
+        expect(commands.some((c) => c.includes(' list-panes -a '))).toBe(true);
+        expect(commands.filter((c) => /show-options -gv prefix|list-keys|unbind-key|bind-key/.test(c))).toEqual([]);
+      } finally {
+        nonTestManager.destroy();
+      }
+    });
+  });
+
+  describe('tmux launch cwd hardening', () => {
     beforeEach(() => {
       mockedExecSync.mockImplementation((cmd: string) => {
         if (typeof cmd === 'string' && cmd.includes('which tmux')) {