Align JSON-RPC and agent-card parsing with cross-SDK interoperability expectations

[muscariello]

Summary

CSIT Rust <-> Go interoperability work surfaced two upstream compatibility gaps in a2a-rs that currently require test-side shims to get clean cross-SDK interop.

Context

Observed while implementing agntcy/csit#163 for Rust <-> Go interoperability validation.

Gaps

1. JSON-RPC method name mismatch

The current Rust JSON-RPC transport/router uses dotted method names such as:

• message.send
• message.stream
• tasks.get
• tasks.list
• tasks.cancel
• tasks.resubscribe

The Go SDK currently emits/specifies CamelCase method names such as:

• SendMessage
• SendStreamingMessage
• GetTask
• ListTasks
• CancelTask
• SubscribeToTask

In practice, Go -> Rust JSON-RPC calls fail with method not found unless the Rust side is wrapped in a compatibility shim.

2. Strict agent card parsing

The Rust AgentCard type currently expects a concrete Vec<AgentSkill> for skills, while Go agent cards may serialize skills: null.

That causes strict Rust deserialization of otherwise usable cross-SDK agent cards to fail, even when the Rust client only needs the JSON-RPC interface URL.

Expected behavior

a2a-rs should interoperate cleanly with other A2A SDKs without requiring CSIT-specific protocol shims for basic JSON-RPC and agent-card exchange.

Suggested scope

• Decide and document the canonical JSON-RPC method names for A2A v1.
• Update the Rust JSON-RPC server/client edges to support the interoperable method names.
• If compatibility matters, consider accepting both the existing dotted names and the spec-style CamelCase names.
• Relax agent card deserialization so skills: null is handled equivalently to an empty list, or otherwise make incoming card parsing tolerant where the field is optional in practice.
• Add regression coverage for cross-SDK cards and JSON-RPC requests.

Impact

This currently blocks clean Rust <-> Go interoperability without fixture-specific compatibility code, and will likely affect broader multi-SDK CSIT work as more languages are added.