fix: persist API server sessions to shared SessionDB (state.db) (#4802)

The API server adapter created AIAgent instances without passing
session_db, so conversations via Open WebUI and other OpenAI-compatible
frontends were never persisted to state.db. This meant 'hermes sessions
list' showed no API server sessions — they were effectively stateless.

Changes:
- Add _ensure_session_db() helper for lazy SessionDB initialization
- Pass session_db=self._ensure_session_db() in _create_agent()
- Refactor existing X-Hermes-Session-Id handler to use the shared helper

Sessions now persist with source='api_server' and are visible alongside
CLI and gateway sessions in hermes sessions list/search.

gateway/platforms/api_server.py

@@ -372,6 +372,24 @@ class APIServerAdapter(BasePlatformAdapter):
             status=401,
         )
 
+    # ------------------------------------------------------------------
+    # Session DB helper
+    # ------------------------------------------------------------------
+
+    def _ensure_session_db(self):
+        """Lazily initialise and return the shared SessionDB instance.
+
+        Sessions are persisted to ``state.db`` so that ``hermes sessions list``
+        shows API-server conversations alongside CLI and gateway ones.
+        """
+        if self._session_db is None:
+            try:
+                from hermes_state import SessionDB
+                self._session_db = SessionDB()
+            except Exception as e:
+                logger.debug("SessionDB unavailable for API server: %s", e)
+        return self._session_db
+
     # ------------------------------------------------------------------
     # Agent creation helper
     # ------------------------------------------------------------------
@@ -415,6 +433,7 @@ class APIServerAdapter(BasePlatformAdapter):
             platform="api_server",
             stream_delta_callback=stream_delta_callback,
             tool_progress_callback=tool_progress_callback,
+            session_db=self._ensure_session_db(),
         )
         return agent
 
@@ -503,10 +522,9 @@ class APIServerAdapter(BasePlatformAdapter):
         if provided_session_id:
             session_id = provided_session_id
             try:
-                if self._session_db is None:
-                    from hermes_state import SessionDB
-                    self._session_db = SessionDB()
-                history = self._session_db.get_messages_as_conversation(session_id)
+                db = self._ensure_session_db()
+                if db is not None:
+                    history = db.get_messages_as_conversation(session_id)
             except Exception as e:
                 logger.warning("Failed to load session history for %s: %s", session_id, e)
                 history = []