feat: Add support for more Task Message and Artifact fields in the Vertex Task Store

[gaborfeher]

WIP

For #751

[github-actions]

🧪 Code Coverage (vs main)

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	Base	PR	Delta
src/a2a/contrib/tasks/vertex_task_converter.py	96.36%	90.91%	🔴 -5.45%
Total	91.73%	91.65%	🔴 -0.08%

Generated by coverage-comment.yml

[gemini-code-assist]

Code Review

This pull request enhances the Vertex AI task converter by implementing comprehensive metadata handling and message conversion logic. It introduces versioned metadata packing/unpacking and updates artifact and task conversion to include fields such as name, description, and status details. Review feedback highlights a potential Pydantic validation error when handling invalid roles in to_sdk_message and suggests improving naming consistency for reference task IDs within the metadata dictionary.

[gemini-code-assist]

The role field in the Message model is required, but this logic allows role to be None if stored_msg.role is invalid, not present, or an empty string. This will cause a pydantic.ValidationError at runtime when Message is instantiated. The # type: ignore on line 276 suppresses the static type error, but hides this potential runtime crash.

To ensure type safety and prevent runtime errors, you should handle the case where a valid Role cannot be determined more explicitly by raising a ValueError.

    try:
        role = Role(stored_msg.role)
    except (ValueError, TypeError) as e:
        raise ValueError(f"Invalid or missing role in stored message: {stored_msg.role!r}") from e

References

1. For unsupported input values, fail explicitly by raising an error instead of silently falling back to a default value.

[gemini-code-assist]

For consistency with the Message model's field name (reference_task_ids), it would be clearer to use 'reference_task_ids' as the key here. This would improve readability and reduce potential confusion.

This change would also require updating the key used in to_sdk_message on line 278 from 'reference_tasks' to 'reference_task_ids'.

Suggested change

	'reference_tasks': stored_metadata.get(_REFERENCE_TASK_IDS_KEY),
	'reference_task_ids': stored_metadata.get(_REFERENCE_TASK_IDS_KEY),