Python: [AG-UI]: TEXT_MESSAGE_END is not emitted when using the MCP tool

[TsukasaIshimura]

I'm building a web app using Microsoft Agent Framework AG-UI and CopilotKit.
When I use the MCP tool, the AG-UI protocol event TEXT_MESSAGE_END is not emitted.

Expected:
Both TEXT_MESSAGE_START and TEXT_MESSAGE_END are emitted.

Actual:
Only TEXT_MESSAGE_START is emitted; TEXT_MESSAGE_END is never emitted.

Could you please look into this? Thank you.

Log
Two TEXT_MESSAGE_START events are emitted, but only one TEXT_MESSAGE_END event is emitted.

curl -N http://127.0.0.1:8000/api/v1/agents/my-agent \
  -H "Content-Type: application/json" \
  -H "Accept: text/event-stream" \
  -d '{
    "threadId": "thread_001",
    "runId": "run_001",
    "messages": [{"role": "user", "content": "Please tell me the current time."}]
  }'
  

data: {"type":"RUN_STARTED","threadId":"fc984c41-071d-45a5-a454-c8382d3b1bf8","runId":"chatcmpl-D4NdyYh2qbRIt8a1a5QgscDOI15f2"}

data: {"type":"TEXT_MESSAGE_START","messageId":"b0fa26a6-142f-4abe-bce0-16dd45f1a14f","role":"assistant"}

data: {"type":"TOOL_CALL_START","toolCallId":"call_ByVpdkal33OO72zsMUEJm2dC","toolCallName":"get_datetime","parentMessageId":"b0fa26a6-142f-4abe-bce0-16dd45f1a14f"}

data: {"type":"TOOL_CALL_ARGS","toolCallId":"call_ByVpdkal33OO72zsMUEJm2dC","delta":"{}"}

data: {"type":"TOOL_CALL_END","toolCallId":"call_ByVpdkal33OO72zsMUEJm2dC"}

data: {"type":"TOOL_CALL_RESULT","messageId":"e1f8871f-3173-43de-9464-1c2aedd35c00","toolCallId":"call_ByVpdkal33OO72zsMUEJm2dC","content":"[{\"type\": \"text\", \"text\": \"2025/12/01 12:00:00\"}]","role":"tool"}

data: {"type":"TEXT_MESSAGE_START","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","role":"assistant"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"The"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" current"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" date"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" and"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" time"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" ("}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"according"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" to"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" my"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" system"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" clock"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":")"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" is"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" "}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"202"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"5"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"-"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"12"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"-"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"01"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" "}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"12"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":":"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"00"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":":"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"00"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"."}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" Would"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" you"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" like"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" this"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" in"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" a"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" specific"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" timezone"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" or"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":" format"}

data: {"type":"TEXT_MESSAGE_CONTENT","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","delta":"?"}

data: {"type":"TEXT_MESSAGE_END","messageId":"3c32c12c-051c-4885-bf75-03bfb1da9cc7"}

data: {"type":"MESSAGES_SNAPSHOT","messages":[{"id":"94eb1979-a7db-41d5-8a84-5505a1405dfb","role":"user","content":"Please tell me the current time."},{"id":"3c32c12c-051c-4885-bf75-03bfb1da9cc7","role":"assistant","content":"The current date and time (according to my system clock) is 2025-12-01 12:00:00. Would you like this in a specific timezone or format?","toolCalls":[{"id":"call_ByVpdkal33OO72zsMUEJm2dC","type":"function","function":{"name":"get_datetime","arguments":"{}"}}]},{"id":"e1f8871f-3173-43de-9464-1c2aedd35c00","role":"tool","content":"[{\"type\": \"text\", \"text\": \"2025/12/01 12:00:00\"}]","toolCallId":"call_ByVpdkal33OO72zsMUEJm2dC"}]}

data: {"type":"RUN_FINISHED","threadId":"fc984c41-071d-45a5-a454-c8382d3b1bf8","runId":"chatcmpl-D4NdyYh2qbRIt8a1a5QgscDOI15f2"}

Source code

get_datetime_mcp = MCPStreamableHTTPTool(
    name="get-datetime-mcp",
    url="http://localhost:8001/mcp",
)

base_agent = ChatAgent(
    name="MyAgent",
    instructions="You are a helpful AI Agent.",
    chat_client=chat_client,
    tools=[get_datetime_mcp],
)

add_agent_framework_fastapi_endpoint(
    app=app,
    agent=AgentFrameworkAgent(
        agent=base_agent,
        name="MyAgent",
        description="Helpful AI Agent",
    ),
    path="/api/v1/agents/my-agent",
)

Version information
Python 3.13.10
agent-framework-ag-ui==1.0.0b260130
agent-framework-core==1.0.0b260130

Thank you in advance.