feat(server): validate presence according to google.api.field_behavior annotations

[ishymko]

Fixes #845

[gemini-code-assist]

Summary of Changes

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This pull request significantly improves the robustness of the server by introducing automatic validation of incoming request parameters. By leveraging google.api.field_behavior annotations, the server now enforces the presence of required fields in Protobuf messages. This change ensures data integrity at the API boundary and provides clients with structured, actionable feedback when validation fails, streamlining the development and debugging experience.

Highlights

• Server-Side Protobuf Validation: Implemented server-side validation for incoming Protobuf messages, enforcing the presence of required fields based on google.api.field_behavior annotations.
• Automated Validation Decorator: Introduced a validate_request_params decorator that automatically applies validation to RequestHandler methods, streamlining the integration of validation logic.
• Enhanced Error Reporting: Improved gRPC and JSON-RPC error handling to include detailed validation errors in the response data field, providing clients with structured and actionable feedback.
• Comprehensive Testing: Added new unit and integration tests to thoroughly cover the new validation logic and ensure correct error reporting across different scenarios.

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[gemini-code-assist]

Code Review

This pull request introduces a robust validation mechanism for incoming Protobuf messages based on google.api.field_behavior annotations. The changes correctly propagate detailed validation errors through both gRPC and JSON-RPC transport layers, providing more informative feedback to clients. The addition of the validate_request_params decorator centralizes this validation logic, ensuring consistency across request handlers. The accompanying tests adequately cover the new validation functionality, including edge cases like missing required fields and nested message validation. Overall, this is a significant improvement for API robustness and developer experience.

[github-actions]

🧪 Code Coverage (vs 1.0-dev)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/client/transports/grpc.py	89.23%	90.14%	🟢 +0.91%
src/a2a/client/transports/jsonrpc.py	86.71%	86.81%	🟢 +0.09%
src/a2a/client/transports/rest.py	91.52%	92.73%	🟢 +1.21%
src/a2a/server/request_handlers/default_request_handler.py	96.89%	96.99%	🟢 +0.10%
src/a2a/server/request_handlers/grpc_handler.py	94.48%	94.89%	🟢 +0.41%
src/a2a/server/request_handlers/request_handler.py	100.00%	90.48%	🔴 -9.52%
src/a2a/server/request_handlers/rest_handler.py	93.75%	94.12%	🟢 +0.37%
src/a2a/utils/proto_utils.py	91.23%	90.36%	🔴 -0.87%
Total	91.45%	91.49%	🟢 +0.04%

Generated by coverage-comment.yml