refactor(ssh): drop probe-only bookkeeping the probe never reads

- probe_only is consumed inside __init__ only; no instance attribute.
- _sync_manager is assigned only on the probe branch, after the connection is
  up, so a normal SSHEnvironment whose constructor fails still behaves exactly
  as before (its __del__ cleanup does not reach the shared socket teardown).
- _remote_home has no reader on the probe path; not assigned.
- prompt_builder passes probe_only=True unconditionally: which backends honor
  it is the builder table's decision, not a caller-side env_type check.
- Tests trimmed to the probe_only contract: the cleanup-raises case was green
  on main (pre-existing try/except), the socket-name length and double-cleanup
  assertions covered pre-existing behaviour.

agent/prompt_builder.py

@@ -876,10 +876,10 @@ def _run_backend_probe(env_type: str, terminal_tool) -> str:
         container_config=(_container_config_from_config(config)
                           if terminal_tool._is_container_backend(env_type) else None),
         task_id="prompt-backend-probe", host_cwd=config.get("host_cwd"),
-        # ssh: an isolated ControlMaster socket and no remote dir setup / file sync / snapshot —
-        # a normal SSHEnvironment would upload the whole ~/.hermes tree just to run `uname`, and
-        # its later __del__ would sync_back() and close the master shared with the agent's own env.
-        probe_only=env_type == "ssh",
+        # Only ssh honors this: an isolated ControlMaster socket and no remote dir setup / file sync /
+        # snapshot. A normal SSHEnvironment would upload the whole ~/.hermes tree just to run `uname`,
+        # and its later __del__ would sync_back() and close the master shared with the agent's own env.
+        probe_only=True,
     )
     try:
         result = env.execute(_BACKEND_PROBE_CMD, timeout=4)

tests/agent/test_prompt_builder.py

@@ -970,27 +970,6 @@ class TestEnvironmentHints:
         assert created["probe_only"] is True
         assert calls == ["cleanup"]
 
-    def test_probe_remote_backend_ssh_cleanup_error_keeps_result(self, monkeypatch):
-        """A failing teardown of the throwaway probe connection must not discard the
-        metadata the probe already collected."""
-        import agent.prompt_builder as _pb
-
-        monkeypatch.setenv("TERMINAL_ENV", "ssh")
-        _pb._clear_backend_probe_cache()
-
-        class _Env:
-            def execute(self, cmd, timeout=None):
-                return {"returncode": 0, "output": "os=Linux\nkernel=6.8.0\nhome=/h\ncwd=/h\nuser=u\n"}
-
-            def cleanup(self):
-                raise RuntimeError("cleanup failed")
-
-        import tools.terminal_tool_backends as _tt
-        monkeypatch.setattr(_tt, "_create_environment", lambda **kw: _Env())
-
-        assert "Linux 6.8.0" in _pb._probe_remote_backend("ssh")
-
-
     def test_environment_hint_from_env_var_is_appended(self, monkeypatch):
         """HERMES_ENVIRONMENT_HINT lets an embedder describe the runtime env."""
         import agent.prompt_builder as _pb

tests/tools/test_ssh_environment.py

@@ -261,7 +261,6 @@ class TestSSHProbeOnly:
         _mock_ssh_runtime["_ensure_remote_dirs"].assert_not_called()
         _mock_ssh_runtime["sync_factory"].assert_not_called()
         _mock_ssh_runtime["init_session"].assert_not_called()
-        assert env._sync_manager is None
 
     def test_probe_only_control_socket_is_isolated(self, monkeypatch, _mock_ssh_runtime):
         control_exit_calls = []
@@ -283,12 +282,10 @@ class TestSSHProbeOnly:
         normal.control_socket.touch()
         first_probe.control_socket.touch()
         first_probe.cleanup()
-        first_probe.cleanup()
 
         assert normal.control_socket.exists()
         assert not first_probe.control_socket.exists()
         assert len(control_exit_calls) == 1
-        normal.cleanup()
 
 
 def _setup_ssh_env(monkeypatch, persistent: bool):

tools/environments/ssh.py

@@ -48,7 +48,6 @@ class SSHEnvironment(BaseEnvironment):
     Spawn-per-call: every execute() spawns a fresh ``ssh ... bash -c`` process.
     Session snapshot preserves env vars across calls; CWD persists via in-band
     stdout markers. Uses SSH ControlMaster for connection reuse.
-    Probe-only instances use an isolated connection without sync or session state.
     """
 
     # Passthrough values are re-forwarded on every command (see _run_bash), so like docker/local
@@ -60,8 +59,6 @@ class SSHEnvironment(BaseEnvironment):
                  probe_only: bool = False):
         super().__init__(cwd=cwd, timeout=timeout)
         self.host, self.user, self.port, self.key_path = host, user, port, key_path
-        self._probe_only = probe_only
-        self._sync_manager = None
         self.control_dir = Path(tempfile.gettempdir()) / "hermes-ssh"
         self.control_dir.mkdir(parents=True, exist_ok=True)
         # Short, deterministic socket name: the path must stay under macOS's 104-byte sun_path
@@ -69,16 +66,15 @@ class SSHEnvironment(BaseEnvironment):
         # stability across reconnects keeps ControlMaster reuse working. A probe gets its own
         # per-instance socket so its cleanup() can never close the agent's shared master.
         socket_key = f"{user}@{host}:{port}"
-        if self._probe_only:
+        if probe_only:
             socket_key = f"{socket_key}:probe:{self._session_id}"
         _socket_id = hashlib.sha256(socket_key.encode()).hexdigest()[:16]
         self.control_socket = self.control_dir / f"{_socket_id}.sock"
         _ensure_ssh_available()
         self._establish_connection()
-        if self._probe_only:
-            self._remote_home = ""
+        if probe_only:
+            self._sync_manager = None
             return
-
         self._remote_home = self._detect_remote_home()
         self._ensure_remote_dirs()
         self._sync_manager = FileSyncManager(