Python version not added to the Agent Engine update query mask

[adrian-codexhealth]

Environment details

• OS type and version: Mac OS 26.1
• Python version: 3.12
• pip version: 25.2
• google-cloud-aiplatform version: 1.129.0

Steps to reproduce

1. Use vertexai.Client(project=..., location=...).agent_engine.update(agent=..., config={'python-version': ...}).
2. The python version is not added to the update mask for the update query to aiplatform.
3. The python version used by the agent engine is not updated.

In the code, the python_version package spec is set in the query payload but not the in the update_mask.

python-aiplatform/vertexai/_genai/agent_engines.py

Lines 1092 to 1101 in 3eb38bf

	# Update the package spec.
	update_masks.append("spec.package_spec.pickle_object_gcs_uri")
	package_spec = {
	"python_version": sys_version,
	"pickle_object_gcs_uri": "{}/{}/{}".format(
	staging_bucket,
	gcs_dir_name,
	_agent_engines_utils._BLOB_FILENAME,
	),
	}