test(ssh-gate): assert SSHGate.stop is no-op on missing sidecar

PRD 0007: the launch ExitStack calls gate.stop on every failure
path, so an early bring-up error (where the gate container was
never created) must not raise from teardown. Mirrors the existing
DockerPipelockProxy.stop assertion.

The orphan-container enumeration in cleanup.py already covers
ssh-gate containers via its `claude-bottle-` name prefix filter —
no code change there.

tests/integration/test_orphan_cleanup.py

@@ -1,8 +1,8 @@
 """Integration: the cleanup primitives the start-flow trap depends on
 are idempotent. The original orphan-network bug was a trap-ordering
 issue; the fix moved the install earlier. The trap is only safe if
-network_remove and PipelockProxy.stop are no-ops against missing
-resources."""
+network_remove, PipelockProxy.stop, and SSHGate.stop are no-ops
+against missing resources."""
 
 import os
 import subprocess
@@ -17,6 +17,10 @@ from claude_bottle.backend.docker.pipelock import (
     DockerPipelockProxy,
     pipelock_container_name,
 )
+from claude_bottle.backend.docker.ssh_gate import (
+    DockerSSHGate,
+    ssh_gate_container_name,
+)
 from tests._docker import skip_unless_docker
 
 
@@ -75,6 +79,13 @@ class TestOrphanCleanup(unittest.TestCase):
         # Should not raise.
         DockerPipelockProxy().stop(pipelock_container_name(f"missing-{self.slug}"))
 
+    def test_ssh_gate_stop_missing_sidecar(self):
+        # Same trap-safety requirement for the gate (PRD 0007). The
+        # launch ExitStack calls gate.stop on every error path; if
+        # the container was never created (early failure), stop must
+        # still no-op.
+        DockerSSHGate().stop(ssh_gate_container_name(f"missing-{self.slug}"))
+
 
 if __name__ == "__main__":
     unittest.main()