fix(shell,remote-ssh): allowlist the login flags, and keep only CRASHED remote panes

Follow-up to #209 and #210. Both land a real fix (a pane that is a login shell
picks up /etc/profile and the per-user PATH entries an ssh remote command never
sees, which is what was failing agent CLIs with exit 127). Three corrections:

1. `-i -l` is no longer hardcoded onto the resolved shell. That path ultimately
   comes from the passwd entry, which is user data and can name anything, and a
   shell that rejects an unknown flag exits on the spot: nushell, elvish and xonsh
   take neither flag, so a user with one of those in passwd would have gotten a
   dead pane on arrival, which is exactly the #208 failure #209 builds on top of.
   loginShellArgs() applies them only to the POSIX-family shells verified to
   accept both, and a test really launches every allowlisted shell present on the
   machine rather than trusting the set. csh/tcsh are excluded deliberately: tcsh
   honors -l only when it is the ONLY flag.

2. `remain-on-exit on` -> `failed`, moved LAST in the tmux command chain. `on`
   keeps the pane after a CLEAN exit too, so typing `exit` in a remote shell
   stranded a dead pane, the session outlived it, and the next launch's `-A`
   reattached to that corpse: "Pane is dead (status 0)" instead of a shell,
   permanently, on the DEFAULT path. Verified against a real tmux, as was the
   fix: `failed` tears the session down on status 0 and keeps the pane on 127
   with the "command not found" still on screen, which is the case #210 wanted.
   It is last because tmux aborts the remaining commands of a `\;` sequence once
   one errors (also verified) and `failed` needs tmux >= 3.2 on the REMOTE host;
   leading, a rejection there would have silently dropped status/mouse/prefix/
   escape-time/window-size along with it.

3. `$SHELL` -> `"${SHELL:-/bin/sh}"`, via one shared remoteLoginShellCommand()
   helper instead of the string being rebuilt in tmux-manager as well.

Also corrects the rationale both PRs carried: a tmux pane already hands the shell
a tty, so it was interactive all along ($- contains i for a bare /bin/bash in a
pane) and ~/.bashrc was always being sourced. `-l` is the flag doing the work.

End-to-end verified, not just unit-tested: the emitted remote pane command was
run through all three quoting layers under a minimal sshd-style PATH with the
CLI installed only on a login-shell PATH entry, and it resolved and launched the
CLI with its arguments intact and a space-containing remote path preserved.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/remote-hosts.ts

@@ -58,6 +58,37 @@ export async function writeRemoteCases(configDir: string, cases: RemoteCase[]):
   await writeJsonArray(configDir, remoteCasesPath(configDir), cases);
 }
 
+/**
+ * The remote user's login shell, defaulted and quoted.
+ *
+ * The default is belt-and-braces, not a live bug: an empty `$SHELL` would expand
+ * to `exec  -i -l`, which the shell reads as `exec -i` — "not found", pane dead on
+ * arrival, the #208 failure all over again (verified: `sh -c 'exec $SHELL -i -l'`
+ * with SHELL unset prints `exec: -i: not found`). In practice tmux always exports
+ * SHELL into a pane from its own `default-shell` option, so the command as USED
+ * here is safe either way (also verified). The default matters because these
+ * strings are the seed values a per-host `commands.*` override is edited from, and
+ * nothing constrains where an edited one ends up running. Quoted for a shell path
+ * containing spaces. `/bin/sh` exists on every POSIX host.
+ */
+const REMOTE_LOGIN_SHELL = '"${SHELL:-/bin/sh}"';
+
+/**
+ * Run `command` through the remote user's interactive login shell, so per-user
+ * PATH entries (~/.local/bin, ~/.opencode/bin, …) are resolved before the CLI name
+ * is looked up. ssh's remote-command execution is neither interactive nor login,
+ * so a bare `exec claude` sees only sshd's minimal default PATH and dies with
+ * "command not found" (exit 127).
+ *
+ * Shells that take neither flag (nushell, elvish, …) cannot be detected from here
+ * the way `loginShellArgs()` detects them locally, since the shell is whatever the
+ * REMOTE passwd says. A host like that is what the per-host `commands.*` override
+ * is for.
+ */
+export function remoteLoginShellCommand(command: string): string {
+  return `exec ${REMOTE_LOGIN_SHELL} -i -l -c ${shellescape(command)}`;
+}
+
 export function defaultRemoteCommandForMode(mode: SessionMode): string {
   // Agent CLIs (claude/opencode/codex/gemini/antigravity) are typically installed
   // under per-user paths like ~/.local/bin or ~/.opencode/bin, added to PATH only by
@@ -73,15 +104,15 @@ export function defaultRemoteCommandForMode(mode: SessionMode): string {
     // /etc/passwd entry, so this launches their actual login shell (zsh,
     // fish, etc.). -i -l so it sources rc files (~/.zshrc etc.), matching
     // the local shell-mode launch.
-    shell: 'exec $SHELL -i -l',
+    shell: `exec ${REMOTE_LOGIN_SHELL} -i -l`,
     // Mirror the LOCAL claude default so the remote agent runs non-interactively
     // (no trust-folder/permission prompt that nothing on the remote answers). The
     // per-host `commands.claude` override stays the escape hatch.
-    claude: `exec $SHELL -i -l -c ${shellescape('claude --dangerously-skip-permissions')}`,
+    claude: remoteLoginShellCommand('claude --dangerously-skip-permissions'),
-    opencode: `exec $SHELL -i -l -c ${shellescape('opencode')}`,
+    opencode: remoteLoginShellCommand('opencode'),
-    codex: `exec $SHELL -i -l -c ${shellescape('codex')}`,
+    codex: remoteLoginShellCommand('codex'),
-    gemini: `exec $SHELL -i -l -c ${shellescape('gemini')}`,
+    gemini: remoteLoginShellCommand('gemini'),
-    antigravity: `exec $SHELL -i -l -c ${shellescape('agy')}`,
+    antigravity: remoteLoginShellCommand('agy'),
   };
   return commands[mode as RemoteCommandMode] || commands.shell;
 }

src/tmux-manager.ts

@@ -49,7 +49,12 @@ import {
   type DockerCommandMode,
 } from './types.js';
 import { buildEffortCliArgs } from './session-cli-builder.js';
-import { buildSshConnectionArgs, defaultRemoteCommandForMode, remoteSshTarget } from './remote-hosts.js';
+import {
+  buildSshConnectionArgs,
+  defaultRemoteCommandForMode,
+  remoteLoginShellCommand,
+  remoteSshTarget,
+} from './remote-hosts.js';
 import {
   buildDockerBaseArgs,
   buildDockerCreateArgs,
@@ -72,6 +77,7 @@ import {
   resolveGeminiDir,
   resolveAntigravityDir,
   resolveLocalShell,
+  loginShellArgs,
 } from './utils/index.js';
 import type {
   TerminalMultiplexer,
@@ -784,11 +790,15 @@ export function buildSpawnCommand(options: {
   // SERVER process's env — empty in containers and system systemd units, leaving
   // the pane command ending in a dangling `&&` ("syntax error: unexpected end of
   // file", pane dead on arrival). Resolve it in Node and quote the result.
-  // -i -l: interactive login shell, so the resolved shell sources the user's rc
+  // #209: launch it as a LOGIN shell, which is what tmux itself does for a pane
-  // files (~/.zshrc, ~/.bashrc, etc.) instead of running as a bare non-interactive
+  // with no `default-command`, so a Codeman shell tab matches a hand-started tmux
-  // child of the non-interactive `bash -c` that launches the pane — without this,
+  // one. That is what picks up /etc/profile and /etc/profile.d/* — a systemd
-  // aliases, PATH additions, and tool init (zoxide, nvm, etc.) are silently dropped.
+  // --user service never sourced them, so its PATH is what every pane inherited.
-  return `${shellescape(resolveLocalShell())} -i -l`;
+  // The flags come from loginShellArgs() rather than being hardcoded: they are
+  // appended to a path that ultimately comes from the passwd entry, and a shell
+  // that rejects an unknown flag exits on the spot, which is #208 all over again.
+  const shell = resolveLocalShell();
+  return `${shellescape(shell)}${loginShellArgs(shell)}`;
 }
 
 /**
@@ -867,7 +877,7 @@ export function buildRemoteLaunchCommand(options: {
   const modeCommand = override
     ? override
     : mode === 'claude'
-      ? `exec $SHELL -i -l -c ${shellescape(`claude${buildClaudePermissionFlags(claudeMode, allowedTools)}`)}`
+      ? remoteLoginShellCommand(`claude${buildClaudePermissionFlags(claudeMode, allowedTools)}`)
       : defaultRemoteCommandForMode(mode);
   const remoteName = remoteTmuxSessionName(sessionId);
 
@@ -882,14 +892,6 @@ export function buildRemoteLaunchCommand(options: {
   // shared remote tmux server's other sessions keep their own prefix/mouse.
   const tmuxInvocation = [
     `tmux -L ${REMOTE_TMUX_SOCKET} new-session -A -s ${remoteName} -c ${shellescape(remote.remotePath)} ${shellescape(paneCommand)}`,
-    // Without this, tmux's default behavior destroys the pane -> window ->
-    // session (and, being the only session, the whole remote server) the
-    // instant paneCommand exits for ANY reason -- even something transient.
-    // That tears down the local ssh -t attach along with it (dead pane,
-    // status whatever ssh reported), and reconnect's `-A` then creates a
-    // fresh session with no trace of what actually happened. Set first, so
-    // it applies as early as possible after the pane starts.
-    `set -t ${remoteName} remain-on-exit on`,
     `set -t ${remoteName} status off`,
     `set -t ${remoteName} mouse off`,
     `set -t ${remoteName} prefix C-q`,
@@ -901,6 +903,24 @@ export function buildRemoteLaunchCommand(options: {
     // Per-session scoped (`set -t <name>`, matching #145's hardening) so a shared
     // remote tmux server's other sessions keep their own sizing behavior.
     `set -t ${remoteName} window-size latest`,
+    // #210: keep a CRASHED pane so the failure is still on screen. Without this,
+    // tmux destroys the pane -> window -> session (and, being the only session,
+    // the whole remote server) the instant the pane command exits, which tears the
+    // local `ssh -t` attach down with it; reconnect's `-A` then builds a fresh
+    // session and the cycle can repeat as a flap loop with no evidence surviving.
+    // That is how the exit-127 PATH bug fixed above stayed invisible.
+    //
+    // `failed`, NOT `on`: `on` keeps the pane on a CLEAN exit too, so typing
+    // `exit` in a remote shell leaves a dead pane behind, the session outlives it,
+    // and the next launch's `-A` reattaches to that corpse ("Pane is dead (status
+    // 0)") instead of starting a shell — verified against a real tmux. `failed`
+    // keeps the pane only on a non-zero exit, which is exactly the diagnostic case.
+    //
+    // LAST in the chain on purpose: tmux aborts the remaining commands of a `\;`
+    // sequence once one errors (also verified), and `failed` needs tmux >= 3.2 on
+    // the REMOTE host. Trailing, a rejection costs only this option; leading, it
+    // would silently drop status/mouse/prefix/escape-time/window-size with it.
+    `set -t ${remoteName} remain-on-exit failed`,
   ].join(' \\; ');
 
   // ssh runs its trailing args through the remote login shell, so the entire

src/utils/index.ts

@@ -26,7 +26,7 @@ export { isSafePushEndpoint } from './push-endpoint-validation.js';
 export { stringSimilarity, fuzzyPhraseMatch, todoContentHash } from './string-similarity.js';
 export { assertNever } from './type-safety.js';
 export { wrapWithNice } from './nice-wrapper.js';
-export { resolveLocalShell } from './shell-resolver.js';
+export { resolveLocalShell, loginShellArgs } from './shell-resolver.js';
 export { findClaudeDir, getAugmentedPath, getClaudeCliVersion, getClaudeBinaryPath } from './claude-cli-resolver.js';
 export { spawnPtyWithHelperRepair } from './node-pty-repair.js';
 export { resolveOpenCodeDir } from './opencode-cli-resolver.js';

src/utils/shell-resolver.ts

@@ -33,6 +33,18 @@ const FALLBACK_SHELLS = ['/bin/bash', '/bin/zsh', '/bin/sh'];
  */
 const NON_INTERACTIVE_SHELLS = new Set(['nologin', 'false', 'true', 'sync']);
 
+/**
+ * Shells verified to accept BOTH `-i` and `-l`. Deliberately an allowlist, not a
+ * blocklist: a shell that rejects an unknown flag exits immediately, which is the
+ * dead-pane-on-arrival failure this module exists to prevent (#208). The passwd
+ * entry is user data and can name anything — nushell, elvish, and xonsh all take
+ * neither flag in this form, so they get a bare launch instead of a dead tab.
+ *
+ * csh/tcsh are excluded on purpose: tcsh honors `-l` only when it is the ONLY
+ * flag, so `-i -l` would silently not be a login shell there anyway.
+ */
+const LOGIN_FLAG_SHELLS = new Set(['sh', 'bash', 'dash', 'ash', 'zsh', 'ksh', 'ksh93', 'mksh', 'pdksh', 'fish']);
+
 function isUsableShell(candidate: string): boolean {
   if (!candidate.startsWith('/')) return false;
   const base = candidate.slice(candidate.lastIndexOf('/') + 1);
@@ -76,3 +88,24 @@ export function resolveLocalShell(): string {
   // best guess and is far better than emitting an empty command.
   return '/bin/sh';
 }
+
+/**
+ * Flags that make `shellPath` a login shell, or `''` when it takes none we trust.
+ *
+ * A tmux pane already hands the shell a tty, so it is interactive with or without
+ * `-i` (verified: `$-` contains `i` for a bare `/bin/bash` in a pane, which is why
+ * `~/.bashrc` has always been sourced). The flag that actually changes anything is
+ * `-l`: it makes the pane a LOGIN shell, matching what tmux itself does when it
+ * spawns a pane with no `default-command`, and picking up the `/etc/profile` and
+ * `/etc/profile.d/*` PATH entries that a systemd-spawned server never sourced.
+ *
+ * `-i` is kept alongside it because for bash the two select different files —
+ * login reads `~/.bash_profile`, interactive-non-login reads `~/.bashrc` — and
+ * asking for both is the closest thing to "the shell the user actually gets".
+ *
+ * Returns a string ready to append to an already-escaped shell path.
+ */
+export function loginShellArgs(shellPath: string): string {
+  const base = shellPath.slice(shellPath.lastIndexOf('/') + 1);
+  return LOGIN_FLAG_SHELLS.has(base) ? ' -i -l' : '';
+}

test/antigravity-mode.test.ts

@@ -120,6 +120,6 @@ describe('Antigravity mode gates', () => {
     expect(defaultDockerCommandForMode('antigravity')).toBe('exec agy');
     // Routed through an interactive login shell so per-user PATH entries resolve —
     // same fix as the other remote agent CLIs (see defaultRemoteCommandForMode).
-    expect(defaultRemoteCommandForMode('antigravity')).toBe("exec $SHELL -i -l -c 'agy'");
+    expect(defaultRemoteCommandForMode('antigravity')).toBe('exec "${SHELL:-/bin/sh}" -i -l -c \'agy\'');
   });
 });

test/remote-hosts.test.ts

@@ -55,13 +55,15 @@ describe('remote-hosts domain', () => {
   });
 
   it('returns safe mode defaults and remote display values', () => {
-    expect(defaultRemoteCommandForMode('shell')).toBe('exec $SHELL -i -l');
+    expect(defaultRemoteCommandForMode('shell')).toBe('exec "${SHELL:-/bin/sh}" -i -l');
     // Routed through an interactive login shell so per-user PATH entries (e.g.
     // ~/.local/bin, ~/.opencode/bin) resolve — a bare `exec codex` sees only
     // sshd's minimal default PATH and fails with "command not found".
-    expect(defaultRemoteCommandForMode('codex')).toBe("exec $SHELL -i -l -c 'codex'");
+    expect(defaultRemoteCommandForMode('codex')).toBe('exec "${SHELL:-/bin/sh}" -i -l -c \'codex\'');
     // Mirrors the local claude default so the remote agent runs non-interactively.
-    expect(defaultRemoteCommandForMode('claude')).toBe("exec $SHELL -i -l -c 'claude --dangerously-skip-permissions'");
+    expect(defaultRemoteCommandForMode('claude')).toBe(
+      'exec "${SHELL:-/bin/sh}" -i -l -c \'claude --dangerously-skip-permissions\''
+    );
     expect(remoteSshTarget({ id: 'h1', label: 'H1', host: 'box.local', username: 'aamer' })).toBe('aamer@box.local');
     expect(remoteDisplayPath({ username: 'aamer', host: 'box.local', path: '/opt/work' })).toBe(
       'aamer@box.local:/opt/work'

test/remote-ssh-options.test.ts

@@ -150,16 +150,19 @@ describe('COD-107 buildRemoteLaunchCommand — threads connection args', () => {
     const sh = (s: string) => "'" + s.replace(/'/g, "'\\''") + "'";
     const remoteName = `codeman-ssh-${SESSION_ID.slice(0, 8)}`;
     const path = sh('/home/ubuntu/work');
-    const paneCommand = `cd ${path} && exec $SHELL -i -l`;
+    const paneCommand = `cd ${path} && exec "\${SHELL:-/bin/sh}" -i -l`;
     const tmuxInvocation = [
       `tmux -L codeman-remote new-session -A -s ${remoteName} -c ${path} ${sh(paneCommand)}`,
-      `set -t ${remoteName} remain-on-exit on`,
       `set -t ${remoteName} status off`,
       `set -t ${remoteName} mouse off`,
       `set -t ${remoteName} prefix C-q`,
       'set -s escape-time 0',
       // COD-106 — shared/collaborative sizing, per-session scoped (never -g).
       `set -t ${remoteName} window-size latest`,
+      // #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.
+      `set -t ${remoteName} remain-on-exit failed`,
     ].join(' \\; ');
     // Connection args (with the default -o ConnectTimeout=10) sit after -t.
     const expected = `ssh -o BatchMode=yes -t -o ConnectTimeout=10 ${remoteSshTarget(baseRemote)} ${sh(tmuxInvocation)}`;

test/shell-session-launch.test.ts

@@ -17,7 +17,7 @@
 import { describe, it, expect, beforeEach, afterEach } from 'vitest';
 import { execFileSync } from 'node:child_process';
 import { buildSpawnCommand } from '../src/tmux-manager.js';
-import { resolveLocalShell } from '../src/utils/shell-resolver.js';
+import { loginShellArgs, resolveLocalShell } from '../src/utils/shell-resolver.js';
 
 describe('resolveLocalShell', () => {
   const originalShell = process.env.SHELL;
@@ -70,6 +70,40 @@ describe('resolveLocalShell', () => {
   });
 });
 
+describe('loginShellArgs (#209 login flags, allowlisted)', () => {
+  it('asks for a login shell on the POSIX-family shells that accept the flags', () => {
+    for (const shell of ['/bin/sh', '/bin/bash', '/bin/dash', '/usr/bin/zsh', '/usr/local/bin/fish', '/bin/ksh']) {
+      expect(loginShellArgs(shell)).toBe(' -i -l');
+    }
+  });
+
+  it('adds nothing for shells that take neither flag, so the pane cannot die on arrival', () => {
+    // The shell path can come from the passwd entry, which is user data and can
+    // name anything. A shell that rejects an unknown flag exits immediately —
+    // indistinguishable from the #208 dead-pane-on-arrival this module prevents.
+    // csh/tcsh are here too: tcsh honors -l only when it is the ONLY flag.
+    for (const shell of ['/usr/bin/nu', '/usr/bin/elvish', '/usr/bin/xonsh', '/bin/tcsh', '/bin/csh']) {
+      expect(loginShellArgs(shell)).toBe('');
+    }
+  });
+
+  it('really launches for every allowlisted shell present on this machine', () => {
+    // The whole point of the allowlist is that the flags are ACCEPTED, so prove it
+    // against the real binaries rather than trusting the set.
+    for (const shell of ['/bin/sh', '/bin/bash', '/bin/dash', '/usr/bin/zsh', '/bin/ksh']) {
+      let exists = true;
+      try {
+        execFileSync('/bin/sh', ['-c', `test -x ${shell}`]);
+      } catch {
+        exists = false;
+      }
+      if (!exists) continue;
+      const out = execFileSync('/bin/sh', ['-c', `${shell} -i -l -c 'echo ok' 2>/dev/null`], { encoding: 'utf8' });
+      expect(out).toContain('ok');
+    }
+  });
+});
+
 describe('shell-mode spawn command (issue #208)', () => {
   const originalShell = process.env.SHELL;
 
@@ -88,10 +122,12 @@ describe('shell-mode spawn command (issue #208)', () => {
     expect(cmd.trim()).not.toBe('');
   });
 
-  it('launches an interactive login shell, so rc files (~/.zshrc, ~/.bashrc, etc.) are sourced', () => {
+  it('launches a LOGIN shell, matching what tmux does for a pane with no default-command', () => {
-    // Without -i -l, the resolved shell runs as a bare non-interactive child of
+    // A tmux pane already hands the shell a tty, so it is interactive either way
-    // the non-interactive `bash -c` that launches the pane, silently dropping
+    // (`$-` contains `i` for a bare /bin/bash in a pane, which is why ~/.bashrc has
-    // aliases, PATH additions, and tool init (zoxide, nvm, etc.).
+    // always been sourced). `-l` is the flag that changes anything: it is what
+    // picks up /etc/profile and /etc/profile.d/*, which a systemd --user service
+    // never sourced, so its minimal PATH is what every pane used to inherit.
     const cmd = buildSpawnCommand({ mode: 'shell', sessionId: 'abc123de-0000-0000-0000-000000000000' });
     expect(cmd.trim().endsWith('-i -l')).toBe(true);
   });

test/tmux-manager.test.ts

@@ -146,8 +146,16 @@ describe('TmuxManager (unit)', () => {
         sessionId: 'abc123def456',
       });
 
-      expect(command).toContain('exec $SHELL -i -l');
+      expect(command).toContain('exec "${SHELL:-/bin/sh}" -i -l');
-      expect(command).toContain('remain-on-exit on');
+      // `failed`, not `on`: `on` also keeps the pane after a CLEAN exit, so typing
+      // `exit` in a remote shell strands a dead pane that the next launch's `-A`
+      // reattaches to instead of starting a shell.
+      expect(command).toContain('remain-on-exit failed');
+      expect(command).not.toContain('remain-on-exit on');
+      // Last in the chain: tmux aborts the rest of a `\;` sequence after an error,
+      // and `failed` needs tmux >= 3.2 on the REMOTE host. Trailing, a rejection
+      // costs only this option instead of every setting after it.
+      expect(command.trimEnd().endsWith("remain-on-exit failed'")).toBe(true);
     });
 
     it('defaults claude to a non-interactive launch (--dangerously-skip-permissions)', () => {
@@ -161,7 +169,7 @@ describe('TmuxManager (unit)', () => {
       // interactive nor login, so a bare `exec claude` fails with "command not found".
       // The inner quoting is escaped twice over (once per shellescape() layer), so
       // assert on the unescaped substrings rather than the literal quoted form.
-      expect(command).toContain('exec $SHELL -i -l -c');
+      expect(command).toContain('exec "${SHELL:-/bin/sh}" -i -l -c');
       expect(command).toContain('claude --dangerously-skip-permissions');
     });
   });