broken query method in LanggraphAgent class

#### Environment details

- OS type and version: macOS 15.6.1 (24G90)
- Python version: Python 3.11.13
- pip freeze:
annotated-types==0.7.0
anyio==4.12.0
blinker==1.9.0
blockbuster==1.5.26
bottleneck==1.6.0
cachetools==6.2.4
certifi==2025.11.12
cffi==2.0.0
charset-normalizer==3.4.4
click==8.3.1
cloudpickle==3.1.2
cryptography==46.0.3
distro==1.9.0
docstring-parser==0.17.0
filetype==1.2.0
flask==3.1.2
forbiddenfruit==0.1.4
google-api-core==2.28.1
google-auth==2.45.0
google-cloud-aiplatform==1.132.0
google-cloud-appengine-logging==1.7.0
google-cloud-audit-log==0.4.0
google-cloud-bigquery==3.39.0
google-cloud-core==2.5.0
google-cloud-logging==3.13.0
google-cloud-resource-manager==1.15.0
google-cloud-storage==3.7.0
google-cloud-trace==1.17.0
google-crc32c==1.8.0
google-genai==1.56.0
google-resumable-media==2.8.0
googleapis-common-protos==1.72.0
grpc-google-iam-v1==0.14.3
grpcio==1.76.0
grpcio-status==1.76.0
grpcio-tools==1.75.1
h11==0.16.0
httpcore==1.0.9
httpx==0.28.1
httpx-sse==0.4.3
idna==3.11
importlib-metadata==8.7.1
itsdangerous==2.2.0
jinja2==3.1.6
jsonpatch==1.33
jsonpointer==3.0.0
jsonschema-rs==0.29.1
langchain-core==1.2.5
langchain-google-genai==4.1.2
langchain-google-vertexai==3.2.0
langgraph==1.0.5
langgraph-api==0.6.14
langgraph-checkpoint==3.0.1
langgraph-cli==0.4.11
langgraph-prebuilt==1.0.5
langgraph-runtime-inmem==0.20.1
langgraph-sdk==0.3.1
langsmith==0.5.1
markupsafe==3.0.3
numexpr==2.14.1
numpy==2.4.0
opentelemetry-api==1.38.0
opentelemetry-exporter-gcp-logging==1.11.0a0
opentelemetry-exporter-gcp-trace==1.11.0
opentelemetry-exporter-otlp-proto-common==1.38.0
opentelemetry-exporter-otlp-proto-http==1.38.0
opentelemetry-proto==1.38.0
opentelemetry-resourcedetector-gcp==1.11.0a0
opentelemetry-sdk==1.38.0
opentelemetry-semantic-conventions==0.59b0
orjson==3.11.5
ormsgpack==1.12.1
packaging==25.0
proto-plus==1.27.0
protobuf==6.33.2
pyarrow==22.0.0
pyasn1==0.6.1
pyasn1-modules==0.4.2
pycparser==2.23
pydantic==2.12.5
pydantic-core==2.41.5
pyjwt==2.10.1
python-dateutil==2.9.0.post0
python-dotenv==1.2.1
pyyaml==6.0.3
requests==2.32.5
requests-toolbelt==1.0.0
rsa==4.9.1
setuptools==80.9.0
shapely==2.1.2
six==1.17.0
sniffio==1.3.1
sse-starlette==2.1.3
starlette==0.50.0
structlog==25.5.0
tenacity==9.1.2
truststore==0.10.4
typing-extensions==4.15.0
typing-inspection==0.4.2
urllib3==2.6.2
uuid-utils==0.12.0
uvicorn==0.40.0
validators==0.35.0
watchfiles==1.1.1
websockets==15.0.1
werkzeug==3.1.4
xxhash==3.6.0
zipp==3.23.0
zstandard==0.25.0

#### Steps to reproduce

1. Create LangGraph agent and deploy it
2. Get remote agent and try to query it

#### Code example

**Deploy**
```python
from vertexai import agent_engines

agent = LanggraphAgent(
model="gemini-2.0-flash-exp",
model_kwargs={"temperature": 0.2},
runnable_builder=runnable_builder,
)

remote_agent = agent_engines.create(
agent_engine=agent,
requirements=requirements,
extra_packages=["./main.py"],
display_name="Agent",
description="Agent"
)

```

**Query remote agent**
```python

remote_agent = agent_engines.get(
resource_name=f"projects/{PROJECT_ID}/locations/{LOCATION}/reasoningEngines/{REASONING_ENGINE_ID}"
)

response = remote_agent.query(
input=query_str
)
```

#### Stack trace
```
google.api_core.exceptions.FailedPrecondition: 400 Reasoning Engine Execution failed.
Please refer to our documentation (https://cloud.google.com/vertex-ai/generative-ai/docs/agent-engine/troubleshooting/use) for checking logs and other troubleshooting tips.
Error Details: {"detail":"Agent Engine Error: An error occurred during invocation. Exception: No module named 'langchain.load'
```

Thanks!