为什么使用 4B 本地模型的 Agent 第一轮就退出了？

agent = create_agent(
    model=llm,
    tools=[search_web],
    system_prompt=system_prompt,
    response_format=ResponseT,
)

model_name = "gemma4:e4b"
llm = ChatOllama(model=model_name, reasoning=True)

class ResponseT(BaseModel):
    ok: bool
    error: str | None
    answer: str | None

system_prompt = """
You are a direct, concise assistant. 

Use search_web when you do not have necessary information

Arguments for ResponseT:
- ok: true when the question was answered successfully; otherwise false.
- answer: a concise answer when ok is true; otherwise null.
- error: null when ok is true; otherwise a brief explanation of the failure.

After gathering enough information, submit ResponseT instead of continuing
to explain your answer in prose.
"""

input_state: InputAgentState = {
    "messages": [
        HumanMessage(
            "If marathon runner Eliud Kipchoge could maintain his"
            "world record pace indefinitely, how long would it take "
            "him to reach the Moon?"
        )
    ]
}

rtn = agent.invoke(input_state)

# No structured response
print(rtn['structured_response']) # None

# The last response is an AI message with a prose content
type(rtn['messages'][-1]) # langchain_core.messages.ai.AIMessage
print(rtn['messages'][-1].content)
"""
Based on the provided data, here is the calculated time:

**1. Determine Kipchoge's Pace (Speed):**
*   World Record Distance: 42.195 km (42,195 meters)

...

**Answer:**
It would take approximately **2.12 years** (or 775 days) to reach the Moon at his marathon world record pace.
"""

agent = create_agent(
    model=llm,
    tools=[_calc],
    system_prompt=system_prompt,
    response_format=ProviderStrategy(ResponseT), # <-- change this
)

# now it returns a structured output,
# but it is not what you expect
print(rtn['structured_response'])
"""
ResponseT(
  ok=True,
  error=None,
  answer="I need to search for Kipchoge's pace
        and the Earth-Moon distance first.")
"""

# The last response is an AI message with a "JSON content"
type(rtn['messages'][-1]) # langchain_core.messages.ai.AIMessage
print(rtn['messages'][-1].content)
"""
{
  "ok": true,
  "error": null,
  "answer": "I need to search for Kipchoge's pace
        and the Earth-Moon distance first."
}
"""

for m in rtn['messages']:
    m.pretty_print()

print(rtn["messages"][-1].usage_metadata)

{ "input_tokens": 3990, "output_tokens": 612, "total_tokens": 4602 }

================================ Human Message =================================

If marathon runner Eliud Kipchoge could maintain hisworld record pace
indefinitely, how long would it take him to reach the Moon?
================================== Ai Message ==================================
Tool Calls:
  search_web (97108cb0-7ab4-48af-b3ac-f531da111c38)
 Call ID: 97108cb0-7ab4-48af-b3ac-f531da111c3
  Args:
    query: Eliud Kipchoge world record pace speed
================================= Tool Message =================================
Name: search_web

[{"url": "https://www.youtube.com/watch?v=SRYtn0j5ccA", "title": "Runners
Attempt Eliud Kipchoge’s World Record Marathon Pace", "content": "###
Description ... now I cannot stop smiling 500 meters to go he has the help
tally to himself he's the Pacemakers I've let him go as ed", "score": 0.2488585,
 "raw_content": null, "id": "a02059-04"}]
================================== Ai Message ==================================
Tool Calls:
  search_web (7d4f42b6-6057-4d8a-a59a-13a51af231fc)
 Call ID: 7d4f42b6-6057-4d8a-a59a-13a51af231fc
  Args:
    query: average distance to the moon in kilometers
================================= Tool Message =================================
Name: search_web

[{"url": "https://en.wikipedia.org/wiki/Lunar_distance", "title": "Lunar
distance ... hello to eachother.", "score": 0.8655088, "raw_content": null,
"id": "942b1b-01"}]
================================== Ai Message ==================================

The calculation requires the average speed of Eliud Kipchoge during his record
attempt and the average distance to the Moon.

1.  **Kipchoge's Average Speed:** His sub-two-hour run (1:59:40.2) maintained
    an average speed of approximately $21.2 \text{ km/h}$.
2.  **Distance to the Moon:** The average distance from the Earth to the Moon
    is approximately $385,000 \text{ km}$.
3.  **Time Calculation:**
    $$\text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{385,000
    \text{ km}}{21.2 \text{ km/h}} \approx 18,170 \text{ hours}$$

This equates to:
*   $757 \text{ days}$
*   Approximately $2.1 \text{ years}$

It would take him approximately **2.1 years** to reach the Moon at that pace.

{ "input_tokens": 40, "output_tokens": 45, "total_tokens": 85 }

================================ Human Message =================================

If marathon runner Eliud Kipchoge could maintain hisworld record pace indefinitely,
how long would it take him to reach the Moon?
================================== Ai Message ==================================

{
  "ok": true,
  "error": null,
  "answer": "I need to search for Kipchoge's pace and the Earth-Moon distance
            first."
}

{ "input_tokens": 3990, "output_tokens": 612, "total_tokens": 4602 }