feat: add A2A (Agent-to-Agent) Protocol support - #107
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Adds a security-enforced A2A endpoint that proxies JSON-RPC 2.0 requests to upstream A2A agents while enforcing per-agent policies via a CallInterceptor. New module src/a2a/: - executor.rs: A2aProxyExecutor forwards message/send to the upstream A2A server and streams the reply back through the event queue - interceptor.rs: A2aPolicyInterceptor enforces agent identity (x-arbitus-agent header), API key auth (constant-time compare), sliding-window rate limiting, and regex payload filtering - mod.rs: public re-exports Config changes (src/config.rs): - New A2aConfig with upstream URL, mount path, and agent card metadata - A2aAgentCardConfig for name/description/url/version Transport changes (src/transport/http.rs): - with_a2a() builder on both HttpTransport and StreamableHttpTransport - Mounts the ra2a router under the configured path when A2A is enabled Binary changes (src/bin/arbitus.rs): - Constructs A2aProxyExecutor + A2aPolicyInterceptor + ServerState from config and wires them into the transport Tests: - tests/a2a.rs: 11 integration tests covering agent card discovery, message proxying, identity enforcement, API key auth, payload filtering, rate limiting, and MCP endpoint isolation - tests/common/mod.rs: dummy A2A upstream + A2aHarness helper Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Summary
/a2aendpoint that proxies JSON-RPC 2.0 requests to upstream A2A agents via thera2aSDKsrc/a2a/module withA2aProxyExecutor(forwards messages to upstream) andA2aPolicyInterceptor(enforces agent identity, API key auth, rate limiting, and payload filtering)a2a:block in YAML) is optional — existing MCP behaviour is completely unaffected when omittedHttpTransportandStreamableHttpTransportgain awith_a2a()builder to mount the ra2a router at the configured pathTest plan
cargo test --lib— 428 unit tests (14 new ininterceptor.rs)cargo test --test a2a— 11 new integration tests (agent card discovery, message proxying, identity enforcement, API key auth, payload filtering, rate limiting, MCP endpoint isolation)cargo clippy -- -D warnings— no warningscargo fmt --check— no formatting violationsCloses #88