refactor: Separate protobuf dependencies into sensible extras

[vinoo999]

Description

This introduces a proto extra into the package. The core library itself has no direct dependency on protobuf and only rest server and clients require a2a. google-api-core is only a dependency for grpc. Refactor accordingly to reduce dependency mangling introduced by proto for non grpc/rest servers. Assuming a CI regenerates the uv.lock file but can regenerate it otherwise.

This does not follow the runtime validation pattern in #217 as proto dependencies are localized in proto_utils.py.

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[gemini-code-assist]

Summary of Changes

Hello @vinoo999, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly refactors the project's dependency management by isolating protobuf-related packages into a new proto optional dependency. The primary goal is to reduce the core library's dependency footprint, ensuring that protobuf and google-api-core are only installed when explicitly required by components such as gRPC or REST servers. This change prevents unnecessary dependency conflicts and streamlines installations for users who do not utilize protobuf-dependent features, leading to a more modular and efficient dependency structure.

Highlights

• Dependency Refactoring: The core package dependencies have been streamlined by removing protobuf and google-api-core from the main dependencies list in pyproject.toml.
• New proto Optional Dependency: A new optional dependency, proto, has been introduced to encapsulate protobuf requirements, allowing for more granular installation.
• Updated Server Dependencies: The grpc and rest-server optional dependencies now explicitly require the new proto extra, ensuring protobuf-related packages are only installed when needed by these components. A new jsonrpc-server extra was also added, and http-server now depends on jsonrpc-server and rest-server.
• Dynamic Protobuf Imports: The src/a2a/utils/proto_utils.py file has been updated to handle google.protobuf imports dynamically, providing a clear ImportError message that guides users to install the proto extra if the dependency is missing.

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[gemini-code-assist]

Code Review

This pull request effectively refactors the project's dependencies by separating protobuf into an optional [proto] extra. This is a great improvement for users who don't need Protobuf-related functionality, reducing the core dependency footprint. The changes in pyproject.toml correctly move the dependencies, and the try-except block in proto_utils.py provides a clear error message for missing optional dependencies. I have one suggestion in pyproject.toml to further improve the structure and maintainability of the optional dependencies for server implementations.

[holtskinner]

I'm not sure protobuf really needs to be a separate dependency group from grpc

[vinoo999]

can remove the extra altogether if you want to be explicit for the REST and gRPC servers. My goal was removing protobuf dependencies especially for JSON-RPC servers + clients.

If you prefer can do:

jsonrpc-server = ["fastapi>=0.115.2", "sse-starlette", "starlette"]
http-server = ["a2a-sdk[jsonrpc-server]", "protobuf>=5.29.5"]
grpc = ["grpcio>=1.60", "grpcio-tools>=1.60", "grpcio_reflection>=1.7.0", "google-api-core>=1.26.0", "protobuf>=5.29.5"]

[vinoo999]

http-server is a bit confusing naming of the extra now that JSON-RPC is split out but needed for backward compatibility

[holtskinner]

@pstephengoogle Can you review and make sure this follows with current plans for the protocol?