fix: close sibling finalize path for handed-off sessions (#88234)

/simplify-code review found _notify_single_query_session_finalize was
missing the _handed_off_session_ids guard that _should_emit_cleanup_session_finalize
and _emit_interrupted_session_end already had. One-shot CLI queries that
somehow handed off would still finalize the session via this path.

Added guard + test.

cli.py

@@ -1363,6 +1363,10 @@ def _notify_single_query_session_finalize(cli, *, reason: str = "shutdown") -> N
     session_id = getattr(agent, "session_id", None) or getattr(cli, "session_id", None)
     if session_id in _single_query_finalize_attempted_session_ids:
         return
+    # Don't finalize a session that was handed off to the gateway —
+    # the gateway owns the lifecycle now (#88234).
+    if session_id in _handed_off_session_ids:
+        return
 
     try:
         _notify_session_finalize(

tests/cli/test_handoff_cleanup_race.py

@@ -136,3 +136,24 @@ def test_cleanup_finalizes_normal_session():
         cli_mod._run_cleanup()
 
     mock_finalize.assert_called_once()
+
+
+def test_single_query_finalize_skipped_for_handed_off():
+    """_notify_single_query_session_finalize must not fire for a handed-off session."""
+    import cli as cli_mod
+
+    _reset_cli_globals(cli_mod)
+    cli_mod._handed_off_session_ids.add("handoff-session-single")
+
+    agent = MagicMock()
+    agent.session_id = "handoff-session-single"
+    agent.platform = "cli"
+
+    cli_mock = MagicMock()
+    cli_mock.agent = agent
+    cli_mock.session_id = "handoff-session-single"
+
+    with patch("hermes_cli.lifecycle.finalize_session") as mock_finalize:
+        cli_mod._notify_single_query_session_finalize(cli_mock)
+
+    mock_finalize.assert_not_called()