fix(gateway): clear stale runtime error fields after platform recovery

Cherry-picked from PR #2470 by @NaesayerX.

write_runtime_status used None as 'don't change', making it impossible
to clear stale error_code/error_message after platform recovery. Now
uses a sentinel (_UNSET) so None means 'clear this field'. Passing
error_code=None removes the key from the platform payload instead of
leaving haunted error metadata in gateway_state.json.

gateway/status.py

@@ -22,6 +22,7 @@ from typing import Any, Optional
 _GATEWAY_KIND = "hermes-gateway"
 _RUNTIME_STATUS_FILE = "gateway_state.json"
 _LOCKS_DIRNAME = "gateway-locks"
+_UNSET = object()
 
 
 def _get_pid_path() -> Path:
@@ -185,14 +186,19 @@ def write_pid_file() -> None:
 
 def write_runtime_status(
     *,
-    gateway_state: Optional[str] = None,
-    exit_reason: Optional[str] = None,
+    gateway_state: Any = _UNSET,
+    exit_reason: Any = _UNSET,
     platform: Optional[str] = None,
-    platform_state: Optional[str] = None,
-    error_code: Optional[str] = None,
-    error_message: Optional[str] = None,
+    platform_state: Any = _UNSET,
+    error_code: Any = _UNSET,
+    error_message: Any = _UNSET,
 ) -> None:
-    """Persist gateway runtime health information for diagnostics/status."""
+    """Persist gateway runtime health information for diagnostics/status.
+
+    Parameters use an internal sentinel so callers can intentionally clear fields
+    by passing ``None``. This matters when a recovered platform transitions from
+    fatal -> connected/disconnected and stale error metadata must be removed.
+    """
     path = _get_runtime_status_path()
     payload = _read_json_file(path) or _build_runtime_status_record()
     payload.setdefault("platforms", {})
@@ -201,19 +207,25 @@ def write_runtime_status(
     payload["start_time"] = _get_process_start_time(os.getpid())
     payload["updated_at"] = _utc_now_iso()
 
-    if gateway_state is not None:
+    if gateway_state is not _UNSET:
         payload["gateway_state"] = gateway_state
-    if exit_reason is not None:
+    if exit_reason is not _UNSET:
         payload["exit_reason"] = exit_reason
 
     if platform is not None:
         platform_payload = payload["platforms"].get(platform, {})
-        if platform_state is not None:
+        if platform_state is not _UNSET:
             platform_payload["state"] = platform_state
-        if error_code is not None:
-            platform_payload["error_code"] = error_code
-        if error_message is not None:
-            platform_payload["error_message"] = error_message
+        if error_code is not _UNSET:
+            if error_code is None:
+                platform_payload.pop("error_code", None)
+            else:
+                platform_payload["error_code"] = error_code
+        if error_message is not _UNSET:
+            if error_message is None:
+                platform_payload.pop("error_message", None)
+            else:
+                platform_payload["error_message"] = error_message
         platform_payload["updated_at"] = _utc_now_iso()
         payload["platforms"][platform] = platform_payload
 

tests/gateway/test_status.py

@@ -103,6 +103,34 @@ class TestGatewayRuntimeStatus:
         assert payload["platforms"]["telegram"]["error_code"] == "telegram_polling_conflict"
         assert payload["platforms"]["telegram"]["error_message"] == "another poller is active"
 
+    def test_write_runtime_status_clears_stale_platform_error_fields_on_recovery(self, tmp_path, monkeypatch):
+        monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+
+        status.write_runtime_status(
+            gateway_state="startup_failed",
+            exit_reason="telegram conflict",
+            platform="telegram",
+            platform_state="fatal",
+            error_code="telegram_token_lock",
+            error_message="another local Hermes gateway is already using this Telegram bot token",
+        )
+
+        status.write_runtime_status(
+            gateway_state="running",
+            exit_reason=None,
+            platform="telegram",
+            platform_state="connected",
+            error_code=None,
+            error_message=None,
+        )
+
+        payload = status.read_runtime_status()
+        assert payload["gateway_state"] == "running"
+        assert payload["exit_reason"] is None
+        assert payload["platforms"]["telegram"]["state"] == "connected"
+        assert "error_code" not in payload["platforms"]["telegram"]
+        assert "error_message" not in payload["platforms"]["telegram"]
+
 
 class TestScopedLocks:
     def test_acquire_scoped_lock_rejects_live_other_process(self, tmp_path, monkeypatch):