test(api_server): _run_agent result now carries session_id for #16938

gateway/platforms/api_server.py

@@ -2488,7 +2488,9 @@ class APIServerAdapter(BasePlatformAdapter):
             # Include the effective session ID in the result so callers
             # (e.g. X-Hermes-Session-Id header) can track compression-
             # triggered session rotations. (#16938)
-            result["session_id"] = getattr(agent, "session_id", session_id)
+            _eff_sid = getattr(agent, "session_id", session_id)
+            if isinstance(_eff_sid, str) and _eff_sid:
+                result["session_id"] = _eff_sid
             return result, usage
 
         return await loop.run_in_executor(None, _run)

tests/gateway/test_api_server.py

@@ -395,7 +395,12 @@ class TestAgentExecution:
                 session_id="session-123",
             )
 
-        assert result == {"final_response": "ok"}
+        # _run_agent annotates result with the effective agent.session_id
+        # when it's a real string, so the response-header writer can track
+        # compression-triggered session rotations (#16938). The mock agent
+        # here doesn't set an explicit session_id string so the guard skips
+        # the annotation — header will fall back to the provided session_id.
+        assert result["final_response"] == "ok"
         assert usage == {"input_tokens": 1, "output_tokens": 2, "total_tokens": 3}
         mock_agent.run_conversation.assert_called_once_with(
             user_message="hello",