Spec Update for Transport Support

[muscariello]

Goals:

• Define how A2A supports HTTP and non-HTTP transports.
• Introduce PluggableTransport as a spec-level concept.
• Clarify preferred/recommended transport formats.

Contents:

• Update to the transport section of the spec:

  • HTTP REST (JSON) and gRPC (HTTP/2 + protobuf) as preferred.
  • JSON-RPC over non-HTTP (e.g., stdio, WebSocket, AGNTCY SLIM) as supported.
  • HTTP headers must be preserved across transports.

• Definition of PluggableTransport interface (language-agnostic).

• Guidelines for SDKs:

  • Must implement PluggableTransport.
  • Must support HTTP/gRPC on top.
  • Should allow community-contributed transports.

• Update to Agent Card spec to support transport announcement.

Optional Enhancements:

• Include examples of stdio + another transport usage.
• Add a compatibility matrix for features across transports.