fix: lazy-init SessionDB on adapter instance instead of per-request

Reuse a single SessionDB across requests by caching on self._session_db
with lazy initialization. Avoids creating a new SQLite connection per
request when X-Hermes-Session-Id is used. Updated tests to set
adapter._session_db directly instead of patching the constructor.

gateway/platforms/api_server.py

@@ -2,7 +2,7 @@
 OpenAI-compatible API server platform adapter.
 
 Exposes an HTTP server with endpoints:
-- POST /v1/chat/completions        — OpenAI Chat Completions format (stateless)
+- POST /v1/chat/completions        — OpenAI Chat Completions format (stateless; opt-in session continuity via X-Hermes-Session-Id header)
 - POST /v1/responses               — OpenAI Responses API format (stateful via previous_response_id)
 - GET  /v1/responses/{response_id} — Retrieve a stored response
 - DELETE /v1/responses/{response_id} — Delete a stored response
@@ -300,6 +300,7 @@ class APIServerAdapter(BasePlatformAdapter):
         self._runner: Optional["web.AppRunner"] = None
         self._site: Optional["web.TCPSite"] = None
         self._response_store = ResponseStore()
+        self._session_db: Optional[Any] = None  # Lazy-init SessionDB for session continuity
 
     @staticmethod
     def _parse_cors_origins(value: Any) -> tuple[str, ...]:
@@ -502,9 +503,10 @@ class APIServerAdapter(BasePlatformAdapter):
         if provided_session_id:
             session_id = provided_session_id
             try:
-                from hermes_state import SessionDB
-                _db = SessionDB()
-                history = _db.get_messages_as_conversation(session_id)
+                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)
             except Exception as e:
                 logger.warning("Failed to load session history for %s: %s", session_id, e)
                 history = []

tests/gateway/test_api_server.py

@@ -1603,16 +1603,15 @@ class TestSessionIdHeader:
     async def test_provided_session_id_is_used_and_echoed(self, adapter):
         """When X-Hermes-Session-Id is provided, it's passed to the agent and echoed in the response."""
         mock_result = {"final_response": "Continuing!", "messages": [], "api_calls": 1}
+        mock_db = MagicMock()
+        mock_db.get_messages_as_conversation.return_value = [
+            {"role": "user", "content": "previous message"},
+            {"role": "assistant", "content": "previous reply"},
+        ]
+        adapter._session_db = mock_db
         app = _create_app(adapter)
         async with TestClient(TestServer(app)) as cli:
-            with patch.object(adapter, "_run_agent", new_callable=AsyncMock) as mock_run, \
-                 patch("hermes_state.SessionDB") as mock_db_cls:
-                mock_db = MagicMock()
-                mock_db.get_messages_as_conversation.return_value = [
-                    {"role": "user", "content": "previous message"},
-                    {"role": "assistant", "content": "previous reply"},
-                ]
-                mock_db_cls.return_value = mock_db
+            with patch.object(adapter, "_run_agent", new_callable=AsyncMock) as mock_run:
                 mock_run.return_value = (mock_result, {"input_tokens": 0, "output_tokens": 0, "total_tokens": 0})
 
                 resp = await cli.post(
@@ -1634,13 +1633,12 @@ class TestSessionIdHeader:
             {"role": "user", "content": "stored message 1"},
             {"role": "assistant", "content": "stored reply 1"},
         ]
+        mock_db = MagicMock()
+        mock_db.get_messages_as_conversation.return_value = db_history
+        adapter._session_db = mock_db
         app = _create_app(adapter)
         async with TestClient(TestServer(app)) as cli:
-            with patch.object(adapter, "_run_agent", new_callable=AsyncMock) as mock_run, \
-                 patch("hermes_state.SessionDB") as mock_db_cls:
-                mock_db = MagicMock()
-                mock_db.get_messages_as_conversation.return_value = db_history
-                mock_db_cls.return_value = mock_db
+            with patch.object(adapter, "_run_agent", new_callable=AsyncMock) as mock_run:
                 mock_run.return_value = (mock_result, {"input_tokens": 0, "output_tokens": 0, "total_tokens": 0})
 
                 resp = await cli.post(
@@ -1667,6 +1665,8 @@ class TestSessionIdHeader:
     async def test_db_failure_falls_back_to_empty_history(self, adapter):
         """If SessionDB raises, history falls back to empty and request still succeeds."""
         mock_result = {"final_response": "OK", "messages": [], "api_calls": 1}
+        # Simulate DB failure: _session_db is None and SessionDB() constructor raises
+        adapter._session_db = None
         app = _create_app(adapter)
         async with TestClient(TestServer(app)) as cli:
             with patch.object(adapter, "_run_agent", new_callable=AsyncMock) as mock_run, \