feat: Keep only 0.3 compatible endpoints in compat version of AgentCard

[bartek-w]

When generating backward compatible AgentCard format, keep only 0.3 compatible endpoints.
This affects /.well-known/agent-card.json and AgentCard generation in 0.3 compat layer.

Fixes #742

[gemini-code-assist]

Summary of Changes

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This pull request refines the generation of backward-compatible AgentCard formats, specifically ensuring that only endpoints compatible with protocol version 0.3 are included. This change is crucial for maintaining proper functionality when interacting with older systems, particularly for the /.well-known/agent-card.json endpoint and the 0.3 compatibility layer. It centralizes version checking logic and introduces robust error handling for scenarios where no compatible interfaces are found.

Highlights

• Version Compatibility Logic Extraction: The logic for determining legacy protocol versions (0.3.x) has been extracted from ClientFactory into a new, dedicated utility module a2a.compat.v0_3.versions for better modularity and reusability.
• AgentCard Interface Filtering for 0.3 Compatibility: When generating backward-compatible AgentCard formats, the system now explicitly filters supported_interfaces to include only those compatible with protocol version 0.3, ensuring that only relevant endpoints are exposed.
• Robust Error Handling for AgentCard Conversion: Error handling has been introduced in the AgentCard conversion process. If an AgentCard lacks any 0.3 compatible interfaces, a VersionNotSupportedError is raised, which is then gracefully handled by setting an empty compatibility dictionary.
• Updated Client Factory Usage: The client factory has been updated to utilize the newly extracted is_legacy_version utility function, centralizing version checks across the codebase.
• Comprehensive Unit Test Coverage: Extensive unit tests have been added and updated across various modules to cover the new version compatibility logic, AgentCard conversion filtering, and error handling scenarios, ensuring the robustness of these changes.

Changelog

• src/a2a/client/client_factory.py
  • Moved version compatibility logic to a shared utility.
  • Updated transport producers to use the new is_legacy_version function.
• src/a2a/compat/v0_3/conversions.py
  • Imported version utility functions and error types.
  • Standardized protocol version constants.
  • Implemented filtering of AgentCard interfaces to retain only 0.3 compatible ones during conversion.
  • Added error handling for AgentCard conversions lacking compatible interfaces.
• src/a2a/compat/v0_3/versions.py
  • Added a new module to centralize protocol version compatibility checks.
• src/a2a/server/request_handlers/response_helpers.py
  • Implemented error handling for VersionNotSupportedError during AgentCard to dictionary conversion.
• tests/client/transports/test_rest_client.py
  • Refactored imports for ClientCallContext.
  • Cleaned up test code by removing redundant local imports and comments.
• tests/compat/v0_3/test_conversions.py
  • Imported VersionNotSupportedError for testing.
  • Adjusted expected protocol version strings in tests.
  • Added a test case for unsupported AgentCard versions during conversion.
• tests/compat/v0_3/test_grpc_handler.py
  • Updated sample_agent_card fixture to include a 0.3 compatible interface.
  • Adjusted expected AgentCard structure and protocol version in gRPC handler tests.
• tests/compat/v0_3/test_rest_transport.py
  • Simplified conditional logic in mock_stream test helper.
• tests/compat/v0_3/test_versions.py
  • Added comprehensive unit tests for the new is_legacy_version utility function.
• tests/server/request_handlers/test_response_helpers.py
  • Imported AgentInterface for new test cases.
  • Expanded test coverage for agent_card_to_dict to include various interface compatibility scenarios.

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[github-actions]

🧪 Code Coverage (vs 1.0-dev)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/client/client_factory.py	88.89%	89.35%	🟢 +0.46%
src/a2a/server/apps/rest/fastapi_app.py	81.25%	85.42%	🟢 +4.17%
src/a2a/server/apps/rest/rest_adapter.py	77.22%	82.28%	🟢 +5.06%
src/a2a/server/request_handlers/response_helpers.py	95.52%	95.71%	🟢 +0.19%
src/a2a/compat/v0_3/versions.py (new)	—	100.00%	—
Total	89.98%	90.10%	🟢 +0.11%

Generated by coverage-comment.yml

[gemini-code-assist]

Code Review

This pull request refactors the legacy version checking into a centralized is_legacy_version utility function and uses it to filter for v0.3 compatible interfaces when creating a backward-compatible AgentCard. This correctly prevents non-compatible interfaces from being included. The change is well-supported by new and updated tests that cover various scenarios, including cases where no compatible interfaces exist. The overall implementation is solid. I've added one minor suggestion for a micro-optimization.