Populate Codex usage metadata for token accounting (#2585)

backend/tests/test_token_usage_middleware.py

@@ -0,0 +1,32 @@
+from unittest.mock import MagicMock, patch
+
+from langchain_core.messages import AIMessage
+
+from deerflow.agents.middlewares.token_usage_middleware import TokenUsageMiddleware
+
+
+def test_after_model_logs_usage_metadata_counts():
+    middleware = TokenUsageMiddleware()
+    state = {
+        "messages": [
+            AIMessage(
+                content="done",
+                usage_metadata={
+                    "input_tokens": 10,
+                    "output_tokens": 5,
+                    "total_tokens": 15,
+                },
+            )
+        ]
+    }
+
+    with patch("deerflow.agents.middlewares.token_usage_middleware.logger.info") as info_mock:
+        result = middleware.after_model(state=state, runtime=MagicMock())
+
+    assert result is None
+    info_mock.assert_called_once_with(
+        "LLM token usage: input=%s output=%s total=%s",
+        10,
+        5,
+        15,
+    )