Agent executor with Ollama backend always terminates with 'done_reason': 'load' (empty content)

### Checked other resources

- [x] I added a very descriptive title to this issue.
- [x] I used the GitHub search to find a similar question and didn't find it.
- [x] I am sure that this is a bug in LangChain rather than my code.
- [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).
- [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS.

### Example Code

```sh
ollama pull qwen2.5:7b
ollama serve
```

```python
from langchain_ollama import ChatOllama
from langchain_core.messages import HumanMessage
from langgraph.prebuilt import create_react_agent
from langchain_core.runnables.config import RunnableConfig

llm = ChatOllama(model='qwen2.5:7b',
                 temperature=0,
                 base_url='http://localhost:11434')
tools = []
agent = create_react_agent(
    model=llm,
    tools = tools
)
config: RunnableConfig = {
    "configurable": {
        "thread_id":"1"
    }
}

result = agent.invoke(HumanMessage('Hello'), config=config)
print(result["messages"])
```

### Error Message and Stack Trace (if applicable)

_No response_

### Description


I am using `create_react_agent` to create an agent executor that is supposed to call tools.
In the given example, I am not defining any tools, but just want to get back a 'normal' text response from the agent.

When running the script, I get the following output (manually formatted for better readability):
```sh
$ python demo.py 
[
  AIMessage(
    content='',
    additional_kwargs={},
    response_metadata={
      'model': 'qwen2.5:7b',
      'created_at': '2025-05-21T09:37:56.153539017Z',
      'done': True,
      'done_reason':'load',
      'total_duration': None,
      'load_duration': None,
      'prompt_eval_count': None,
      'prompt_eval_duration': None,
      'eval_count': None,
      'eval_duration': None,
      'model_name': 'qwen2.5:7b'
    },
    id='run--b46ba0b2-e87b-494c-bb95-20db8db39139-0')
]
```

Based on the example output given in [How to migrate from legacy LangChain agents to LangGraph](https://python.langchain.com/docs/how_to/migrate_agent/#basic-usage), I would expect the `content` key to be populated with anything other than `''` (an empty string).
In other places I have seen that for a correct response, the `done_reason` was `'stop'`, in my example it is `'load'`.
Is this kind of an intermediate, streamed result? And if so, what can I do to wait for the full response?
What can I do to make this work?

### System Info

System Information
------------------
> OS:  Linux
> OS Version:  #150-Ubuntu SMP Sat Apr 12 06:00:09 UTC 2025
> Python Version:  3.10.12 (main, Feb  4 2025, 14:57:36) [GCC 11.4.0]

Package Information
-------------------
> langchain_core: 0.3.60
> langchain: 0.3.25
> langchain_community: 0.3.24
> langsmith: 0.3.42
> langchain_ollama: 0.3.3
> langchain_text_splitters: 0.3.8
> langgraph_sdk: 0.1.69

Optional packages not installed
-------------------------------
> langserve

Other Dependencies
------------------
> aiohttp<4.0.0,>=3.8.3: Installed. No version info available.
> async-timeout<5.0.0,>=4.0.0;: Installed. No version info available.
> dataclasses-json<0.7,>=0.5.7: Installed. No version info available.
> httpx: 0.28.1
> httpx-sse<1.0.0,>=0.4.0: Installed. No version info available.
> jsonpatch<2.0,>=1.33: Installed. No version info available.
> langchain-anthropic;: Installed. No version info available.
> langchain-aws;: Installed. No version info available.
> langchain-azure-ai;: Installed. No version info available.
> langchain-cohere;: Installed. No version info available.
> langchain-community;: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.51: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.58: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.59: Installed. No version info available.
> langchain-core<1.0.0,>=0.3.60: Installed. No version info available.
> langchain-deepseek;: Installed. No version info available.
> langchain-fireworks;: Installed. No version info available.
> langchain-google-genai;: Installed. No version info available.
> langchain-google-vertexai;: Installed. No version info available.
> langchain-groq;: Installed. No version info available.
> langchain-huggingface;: Installed. No version info available.
> langchain-mistralai;: Installed. No version info available.
> langchain-ollama;: Installed. No version info available.
> langchain-openai;: Installed. No version info available.
> langchain-perplexity;: Installed. No version info available.
> langchain-text-splitters<1.0.0,>=0.3.8: Installed. No version info available.
> langchain-together;: Installed. No version info available.
> langchain-xai;: Installed. No version info available.
> langchain<1.0.0,>=0.3.25: Installed. No version info available.
> langsmith-pyo3: Installed. No version info available.
> langsmith<0.4,>=0.1.125: Installed. No version info available.
> langsmith<0.4,>=0.1.126: Installed. No version info available.
> langsmith<0.4,>=0.1.17: Installed. No version info available.
> numpy>=1.26.2;: Installed. No version info available.
> numpy>=2.1.0;: Installed. No version info available.
> ollama<1.0.0,>=0.4.8: Installed. No version info available.
> openai-agents: Installed. No version info available.
> opentelemetry-api: Installed. No version info available.
> opentelemetry-exporter-otlp-proto-http: Installed. No version info available.
> opentelemetry-sdk: Installed. No version info available.
> orjson: 3.10.18
> packaging: 24.2
> packaging<25,>=23.2: Installed. No version info available.
> pydantic: 2.11.4
> pydantic-settings<3.0.0,>=2.4.0: Installed. No version info available.
> pydantic<3.0.0,>=2.7.4: Installed. No version info available.
> pydantic>=2.7.4: Installed. No version info available.
> pytest: Installed. No version info available.
> PyYAML>=5.3: Installed. No version info available.
> requests: 2.32.3
> requests-toolbelt: 1.0.0
> requests<3,>=2: Installed. No version info available.
> rich: Installed. No version info available.
> SQLAlchemy<3,>=1.4: Installed. No version info available.
> tenacity!=8.4.0,<10,>=8.1.0: Installed. No version info available.
> tenacity!=8.4.0,<10.0.0,>=8.1.0: Installed. No version info available.
> typing-extensions>=4.7: Installed. No version info available.
> zstandard: 0.23.0

Labels: bug
State: closed