fix: cot agent token usage is empty (langgenius#4474)

Author: sinomoe

api/core/agent/cot_agent_runner.py

@@ -121,7 +121,7 @@ def increase_usage(final_llm_usage_dict: dict[str, LLMUsage], usage: LLMUsage):
                 raise ValueError("failed to invoke llm")
 
             usage_dict = {}
-            react_chunks = CotAgentOutputParser.handle_react_stream_output(chunks)
+            react_chunks = CotAgentOutputParser.handle_react_stream_output(chunks, usage_dict)
             scratchpad = AgentScratchpadUnit(
                 agent_response='',
                 thought='',

api/core/agent/output_parser/cot_output_parser.py

@@ -9,7 +9,7 @@
 
 class CotAgentOutputParser:
     @classmethod
-    def handle_react_stream_output(cls, llm_response: Generator[LLMResultChunk, None, None]) -> \
+    def handle_react_stream_output(cls, llm_response: Generator[LLMResultChunk, None, None], usage_dict: dict) -> \
         Generator[Union[str, AgentScratchpadUnit.Action], None, None]:
         def parse_action(json_str):
             try:
@@ -58,6 +58,8 @@ def extra_json_from_code_block(code_block) -> Generator[Union[dict, str], None,
         thought_idx = 0
 
         for response in llm_response:
+            if response.delta.usage:
+                usage_dict['usage'] = response.delta.usage
             response = response.delta.message.content
             if not isinstance(response, str):
                 continue