fix(gateway): recover stale pid and planned restart state

gateway/status.py

@@ -22,11 +22,18 @@ from pathlib import Path
 from hermes_constants import get_hermes_home
 from typing import Any, Optional
 
+if sys.platform == "win32":
+    import msvcrt
+else:
+    import fcntl
+
 _GATEWAY_KIND = "hermes-gateway"
 _RUNTIME_STATUS_FILE = "gateway_state.json"
 _LOCKS_DIRNAME = "gateway-locks"
 _IS_WINDOWS = sys.platform == "win32"
 _UNSET = object()
+_GATEWAY_LOCK_FILENAME = "gateway.lock"
+_gateway_lock_handle = None
 
 
 def _get_pid_path() -> Path:
@@ -35,6 +42,14 @@ def _get_pid_path() -> Path:
     return home / "gateway.pid"
 
 
+def _get_gateway_lock_path(pid_path: Optional[Path] = None) -> Path:
+    """Return the path to the runtime gateway lock file."""
+    if pid_path is not None:
+        return pid_path.with_name(_GATEWAY_LOCK_FILENAME)
+    home = get_hermes_home()
+    return home / _GATEWAY_LOCK_FILENAME
+
+
 def _get_runtime_status_path() -> Path:
     """Return the persisted runtime health/status file path."""
     return _get_pid_path().with_name(_RUNTIME_STATUS_FILE)
@@ -212,6 +227,19 @@ def _read_pid_record(pid_path: Optional[Path] = None) -> Optional[dict]:
     return None
 
 
+def _read_gateway_lock_record(lock_path: Optional[Path] = None) -> Optional[dict[str, Any]]:
+    return _read_pid_record(lock_path or _get_gateway_lock_path())
+
+
+def _pid_from_record(record: Optional[dict[str, Any]]) -> Optional[int]:
+    if not record:
+        return None
+    try:
+        return int(record["pid"])
+    except (KeyError, TypeError, ValueError):
+        return None
+
+
 def _cleanup_invalid_pid_path(pid_path: Path, *, cleanup_stale: bool) -> None:
     if not cleanup_stale:
         return
@@ -224,6 +252,102 @@ def _cleanup_invalid_pid_path(pid_path: Path, *, cleanup_stale: bool) -> None:
         pass
 
 
+def _write_gateway_lock_record(handle) -> None:
+    handle.seek(0)
+    handle.truncate()
+    json.dump(_build_pid_record(), handle)
+    handle.flush()
+    try:
+        os.fsync(handle.fileno())
+    except OSError:
+        pass
+
+
+def _try_acquire_file_lock(handle) -> bool:
+    try:
+        if _IS_WINDOWS:
+            handle.seek(0, os.SEEK_END)
+            if handle.tell() == 0:
+                handle.write("\n")
+                handle.flush()
+            handle.seek(0)
+            msvcrt.locking(handle.fileno(), msvcrt.LK_NBLCK, 1)
+        else:
+            fcntl.flock(handle.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
+        return True
+    except (BlockingIOError, OSError):
+        return False
+
+
+def _release_file_lock(handle) -> None:
+    try:
+        if _IS_WINDOWS:
+            handle.seek(0)
+            msvcrt.locking(handle.fileno(), msvcrt.LK_UNLCK, 1)
+        else:
+            fcntl.flock(handle.fileno(), fcntl.LOCK_UN)
+    except OSError:
+        pass
+
+
+def acquire_gateway_runtime_lock() -> bool:
+    """Claim the cross-process runtime lock for the gateway.
+
+    Unlike the PID file, the lock is owned by the live process itself. If the
+    process dies abruptly, the OS releases the lock automatically.
+    """
+    global _gateway_lock_handle
+    if _gateway_lock_handle is not None:
+        return True
+
+    path = _get_gateway_lock_path()
+    path.parent.mkdir(parents=True, exist_ok=True)
+    handle = open(path, "a+", encoding="utf-8")
+    if not _try_acquire_file_lock(handle):
+        handle.close()
+        return False
+    _write_gateway_lock_record(handle)
+    _gateway_lock_handle = handle
+    return True
+
+
+def release_gateway_runtime_lock() -> None:
+    """Release the gateway runtime lock when owned by this process."""
+    global _gateway_lock_handle
+    handle = _gateway_lock_handle
+    if handle is None:
+        return
+    _gateway_lock_handle = None
+    _release_file_lock(handle)
+    try:
+        handle.close()
+    except OSError:
+        pass
+
+
+def is_gateway_runtime_lock_active(lock_path: Optional[Path] = None) -> bool:
+    """Return True when some process currently owns the gateway runtime lock."""
+    global _gateway_lock_handle
+    resolved_lock_path = lock_path or _get_gateway_lock_path()
+    if _gateway_lock_handle is not None and resolved_lock_path == _get_gateway_lock_path():
+        return True
+
+    if not resolved_lock_path.exists():
+        return False
+
+    handle = open(resolved_lock_path, "a+", encoding="utf-8")
+    try:
+        if _try_acquire_file_lock(handle):
+            _release_file_lock(handle)
+            return False
+        return True
+    finally:
+        try:
+            handle.close()
+        except OSError:
+            pass
+
+
 def write_pid_file() -> None:
     """Write the current process PID and metadata to the gateway PID file.
 
@@ -583,35 +707,42 @@ def get_running_pid(
     Cleans up stale PID files automatically.
     """
     resolved_pid_path = pid_path or _get_pid_path()
-    record = _read_pid_record(resolved_pid_path)
-    if not record:
+    resolved_lock_path = _get_gateway_lock_path(resolved_pid_path)
+    lock_active = is_gateway_runtime_lock_active(resolved_lock_path)
+    if not lock_active:
         _cleanup_invalid_pid_path(resolved_pid_path, cleanup_stale=cleanup_stale)
         return None
 
-    try:
-        pid = int(record["pid"])
-    except (KeyError, TypeError, ValueError):
-        _cleanup_invalid_pid_path(resolved_pid_path, cleanup_stale=cleanup_stale)
-        return None
+    primary_record = _read_pid_record(resolved_pid_path)
+    fallback_record = _read_gateway_lock_record(resolved_lock_path)
 
-    try:
-        os.kill(pid, 0)  # signal 0 = existence check, no actual signal sent
-    except (ProcessLookupError, PermissionError):
-        _cleanup_invalid_pid_path(resolved_pid_path, cleanup_stale=cleanup_stale)
-        return None
+    for record in (primary_record, fallback_record):
+        pid = _pid_from_record(record)
+        if pid is None:
+            continue
 
-    recorded_start = record.get("start_time")
-    current_start = _get_process_start_time(pid)
-    if recorded_start is not None and current_start is not None and current_start != recorded_start:
-        _cleanup_invalid_pid_path(resolved_pid_path, cleanup_stale=cleanup_stale)
-        return None
+        try:
+            os.kill(pid, 0)  # signal 0 = existence check, no actual signal sent
+        except ProcessLookupError:
+            continue
+        except PermissionError:
+            # The process exists but belongs to another user/service scope.
+            # With the runtime lock still held, prefer keeping it visible
+            # rather than deleting the PID file as "stale".
+            if _record_looks_like_gateway(record):
+                return pid
+            continue
 
-    if not _looks_like_gateway_process(pid):
-        if not _record_looks_like_gateway(record):
-            _cleanup_invalid_pid_path(resolved_pid_path, cleanup_stale=cleanup_stale)
-            return None
+        recorded_start = record.get("start_time")
+        current_start = _get_process_start_time(pid)
+        if recorded_start is not None and current_start is not None and current_start != recorded_start:
+            continue
 
-    return pid
+        if _looks_like_gateway_process(pid) or _record_looks_like_gateway(record):
+            return pid
+
+    _cleanup_invalid_pid_path(resolved_pid_path, cleanup_stale=cleanup_stale)
+    return None
 
 
 def is_gateway_running(