refactor: unify on_message_send in server

[ishymko]

JSON-RPC diverged a bit, update it to match other transports. Domain request handler returns Task | Message from on_message_send already.

Fixes #697 (comment).

Re #559.

[gemini-code-assist]

Summary of Changes

Hello @ishymko, 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 refactors the server's on_message_send implementation across various transport protocols (gRPC, JSON-RPC, REST). The primary goal is to align the JSON-RPC handler with other existing transports, ensuring that all handlers consistently process and return Task or Message objects wrapped in a SendMessageResponse. This change simplifies the code by removing redundant logic and comments, leading to a more unified and maintainable codebase for handling outgoing messages.

Highlights

• Unified on_message_send logic: The handling of on_message_send responses has been standardized across gRPC, JSON-RPC, and REST request handlers to ensure consistent behavior.
• Simplified SendMessageResponse creation: The construction of SendMessageResponse objects has been streamlined, directly initializing the response with either a Task or Message object based on the return type from the domain request handler.
• Removed redundant code: Unnecessary comments and an unused Message import have been removed, improving code clarity and reducing clutter.

Changelog

• src/a2a/server/request_handlers/grpc_handler.py
  • Removed a comment that described the SendMessageResponse wrapping logic.
• src/a2a/server/request_handlers/jsonrpc_handler.py
  • Removed the unused Message import.
  • Refactored the on_message_send method to directly construct SendMessageResponse objects, removing intermediate assignments and redundant checks.
• src/a2a/server/request_handlers/rest_handler.py
  • Deleted a comment explaining the wrapping of the result in a SendMessageResponse.

Activity

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[gemini-code-assist]

Code Review

This is a nice refactoring that unifies the logic for handling on_message_send across the different server transports (gRPC, JSON-RPC, and REST). The core change simplifies the jsonrpc_handler to be more direct and consistent with the other handlers, which improves maintainability. The removal of verbose code and unused imports makes the implementation cleaner. Overall, these are solid improvements.