[Bugfix] Fix tool call arguments parsed as content/reasoning in harmony streaming

tests/entrypoints/openai/test_serving_chat.py

@@ -1077,7 +1077,12 @@ def serving_chat(self, mock_engine) -> OpenAIServingChat:
         return chat
 
     def mock_request_output_from_req_and_token_ids(
-        self, req: ChatCompletionRequest, token_ids: list[int], finished: bool = False
+        self,
+        req: ChatCompletionRequest,
+        token_ids: list[int],
+        finished: bool = False,
+        finish_reason: str | None = None,
+        stop_reason: int | str | None = None,
     ) -> RequestOutput:
         # Our tests don't use most fields, so just get the token ids correct
         completion_output = CompletionOutput(
@@ -1086,6 +1091,8 @@ def mock_request_output_from_req_and_token_ids(
             token_ids=token_ids,
             cumulative_logprob=0.0,
             logprobs=None,
+            finish_reason=finish_reason,
+            stop_reason=stop_reason,
         )
         return RequestOutput(
             request_id=req.request_id,
@@ -1130,18 +1137,27 @@ async def generate_response_from_harmony_str(
         req: ChatCompletionRequest,
         harmony_str: str,
         stream: bool = False,
+        terminal_stream_chunk: bool = False,
     ) -> ChatCompletionResponse:
         harmony_token_ids = get_encoding().encode(harmony_str, allowed_special="all")
 
         async def result_generator():
             if stream:
-                for token_id in harmony_token_ids:
+                if terminal_stream_chunk:
                     yield self.mock_request_output_from_req_and_token_ids(
-                        req, [token_id]
+                        req,
+                        harmony_token_ids,
+                        finished=True,
+                        finish_reason="stop",
+                    )
+                else:
+                    for token_id in harmony_token_ids:
+                        yield self.mock_request_output_from_req_and_token_ids(
+                            req, [token_id]
+                        )
+                    yield self.mock_request_output_from_req_and_token_ids(
+                        req, [], finished=True
                     )
-                yield self.mock_request_output_from_req_and_token_ids(
-                    req, [], finished=True
-                )
             else:
                 yield self.mock_request_output_from_req_and_token_ids(
                     req, harmony_token_ids, finished=True
@@ -1377,6 +1393,60 @@ async def test_tools_and_reasoning(
             ],
         )
 
+    @pytest.mark.asyncio
+    @pytest.mark.skip_global_cleanup
+    async def test_streaming_terminal_chunk_recovers_analysis_tool_call(
+        self, serving_chat, weather_tools, weather_messages_start
+    ):
+        tool_args_str = '{"location": "Paris"}'
+        req = ChatCompletionRequest(
+            model=MODEL_NAME,
+            messages=list(weather_messages_start),
+            tools=weather_tools,
+            include_reasoning=False,
+        )
+        serving_chat.tool_parser = None
+        response_str = (
+            "<|start|>assistant to=functions.get_weather<|channel|>analysis"
+            f"<|constrain|>json<|message|>{tool_args_str}<|call|>"
+        )
+
+        response = await self.generate_response_from_harmony_str(
+            serving_chat,
+            req,
+            response_str,
+            stream=True,
+            terminal_stream_chunk=True,
+        )
+
+        verify_chat_response(response, tool_calls=[("get_weather", tool_args_str)])
+        assert response.choices[0].finish_reason == "tool_calls"
+
+    @pytest.mark.asyncio
+    @pytest.mark.skip_global_cleanup
+    async def test_streaming_terminal_chunk_does_not_promote_reasoning_to_content(
+        self, serving_chat, weather_tools, weather_messages_start
+    ):
+        req = ChatCompletionRequest(
+            model=MODEL_NAME,
+            messages=list(weather_messages_start),
+            tools=weather_tools,
+            include_reasoning=False,
+        )
+        serving_chat.tool_parser = None
+        response_str = "<|channel|>analysis<|message|>I'll think about it.<|end|>"
+
+        response = await self.generate_response_from_harmony_str(
+            serving_chat,
+            req,
+            response_str,
+            stream=True,
+            terminal_stream_chunk=True,
+        )
+
+        verify_chat_response(response)
+        assert response.choices[0].finish_reason == "stop"
+
     @pytest.mark.asyncio
     async def test_multi_turn_tools_and_reasoning(
         self, serving_chat, stream, weather_tools, weather_messages_start