(remote): detach by ending the ssh client, not a tmux prefix keystroke

remote-attach.js

@@ -5,8 +5,6 @@
 
 const TMUX_FIELD_RE = /^([A-Za-z0-9._-]{1,64}):(@?\d{1,10}(?:\.%?\d{1,10})?)$/;
 const PROBE_SEP = '\u0001';
-const DETACH_KEYS = '\x02d'; // Ctrl-B d — tmux default prefix, then detach
-const DETACH_GRACE_MS = 150;
 const DEFAULT_PROBE_TIMEOUT_MS = 15000;
 const DEFAULT_STATUS_LINES = 1;
 const NO_TMUX_ENV_EXIT_CODE = 3;
@@ -220,12 +218,15 @@ function createTmuxAttachAdapter(opts = {}) {
     raw.onExit(() => { alive = false; });
 
     let detaching = false;
+    // Ending the local ssh client is what detaches: the remote tmux client
+    // loses its pty and tmux drops it, leaving the session running. Sending a
+    // prefix keystroke instead would assume this host's prefix, and land as
+    // literal text in the remote session on any host that remapped it.
+    // see .ai/contexts/session-cache.md ("Remote hosts — tmux attach")
     function detach() {
       if (detaching || !alive) return;
       detaching = true;
-      try { raw.write(DETACH_KEYS); } catch {}
-      // see .ai/contexts/session-cache.md ("Remote hosts — tmux attach")
-      setTimeout(() => { try { raw.kill(); } catch {} }, DETACH_GRACE_MS);
+      try { raw.kill(); } catch {}
     }
 
     const ptyProcess = {
@@ -264,5 +265,4 @@ module.exports = {
   parseDiscoveryProbeOutput,
   buildProbeCommand,
   buildAttachCommand,
-  DETACH_KEYS,
 };

test/remote-attach.test.js

@@ -206,8 +206,8 @@ test('attach() refuses a descriptor with no readable pid, before any ssh call',
 });
 
 // Property 3 -- the returned ptyProcess is pilotable without any real local
-// node-pty: writes reach the underlying process, and kill() detaches cleanly
-// (Ctrl-B d) before ending the local ssh client, rather than killing outright.
+// node-pty: writes reach the underlying process, and kill() detaches by
+// ending the local ssh client, sending nothing to the remote session.
 test('the returned ptyProcess pilots the fake remote pty through write() and kill()', async () => {
   const raw = fakeRawPty();
   const adapter = makeAdapter({ probeStdout: '200x50' + PROBE_SEP + 'status on', rawPtyFactory: () => raw.pty });
@@ -222,12 +222,13 @@ test('the returned ptyProcess pilots the fake remote pty through write() and kil
   assert.equal(ptyProcess.pid, 4242);
 
   ptyProcess.kill();
-  // Detach sends Ctrl-B d before ending the local client -- see DETACH_KEYS.
-  assert.equal(raw.writes[raw.writes.length - 1], '\x02d', 'kill() must send the tmux detach sequence, not just end the process');
-  assert.equal(raw.killedCount(), 0, 'the local client must not be ended immediately -- see the detach grace period');
-
-  await new Promise((resolve) => setTimeout(resolve, 250));
-  assert.equal(raw.killedCount(), 1, 'the local client must be ended once the detach keystroke has had time to land');
+  // Detaching means ending the local ssh client and nothing else: any prefix
+  // keystroke would assume this host's tmux prefix and land as literal text
+  // in the remote session on a host that remapped it. Measured on the live
+  // host: killing the client alone takes the attached client count back to 0
+  // and leaves the session running.
+  assert.deepEqual(raw.writes, ['echo hi\n'], 'kill() must not send any keystroke to the remote session');
+  assert.equal(raw.killedCount(), 1, 'kill() must end the local ssh client');
   assert.equal(ptyProcess.isAlive(), false);
 });