Fix ssh terminfo spew by using RemoteCommand bootstrap

CLI/cmux.swift

@@ -2121,13 +2121,19 @@ struct CMUXCLI {
         }
 
         if options.extraArguments.isEmpty {
-            // No explicit remote command provided: launch an interactive shell while prepending
-            // ~/.cmux/bin so `cmux` works in this SSH session without touching remote dotfiles.
+            // No explicit remote command provided: keep destination-only argv so Ghostty's
+            // ssh-terminfo bootstrap can safely append its own remote install command.
+            // Use RemoteCommand for session-local PATH bootstrap to make `cmux` available.
             if !hasSSHOptionKey(options.sshOptions, key: "RequestTTY") {
                 parts.append("-tt")
             }
+            if !hasSSHOptionKey(options.sshOptions, key: "RemoteCommand") {
+                parts += [
+                    "-o",
+                    "RemoteCommand=export PATH=\"$HOME/.cmux/bin:$PATH\"; exec \"${SHELL:-/bin/zsh}\" -l",
+                ]
+            }
             parts.append(options.destination)
-            parts.append("export PATH=\"$HOME/.cmux/bin:$PATH\"; exec \"${SHELL:-/bin/zsh}\" -l")
         } else {
             parts.append(options.destination)
             parts.append(contentsOf: options.extraArguments)

tests_v2/test_ssh_remote_cli_metadata.py

@@ -116,6 +116,10 @@ def main() -> int:
             _must("-o ControlMaster=auto" in ssh_command, f"ssh command should opt into connection reuse: {ssh_command!r}")
             _must("-o ControlPersist=600" in ssh_command, f"ssh command should keep master alive for reuse: {ssh_command!r}")
             _must("ControlPath=/tmp/cmux-ssh-" in ssh_command, f"ssh command should use shared control path template: {ssh_command!r}")
+            _must(
+                "RemoteCommand=export PATH=\"$HOME/.cmux/bin:$PATH\"; exec \"${SHELL:-/bin/zsh}\" -l" in ssh_command,
+                f"cmux ssh should use -o RemoteCommand for PATH bootstrap (not positional command): {ssh_command!r}",
+            )
 
             listed_row = None
             deadline = time.time() + 8.0

tests_v2/test_ssh_remote_shell_integration.py

@@ -246,6 +246,11 @@ def main() -> int:
             surfaces = client.list_surfaces(workspace_id)
             _must(bool(surfaces), f"workspace should have at least one surface: {workspace_id}")
             surface_id = surfaces[0][1]
+            terminal_text = client.read_terminal_text(surface_id)
+            _must(
+                "Reconstructed via infocmp" not in terminal_text,
+                "ssh-terminfo bootstrap should not leak raw infocmp output into the interactive shell",
+            )
 
             term_value = _read_probe_payload(client, surface_id, "printf '%s' \"$TERM\"")
             terminfo_state = _read_probe_value(client, surface_id, "infocmp xterm-ghostty >/dev/null 2>&1")