a2a-agents v0.4.0

Added

• (0.4) Finish mcp-client framework integration + a2a-mcp edition 2024
• (a2a-agents) MCP server over Streamable HTTP transport
• (0.4) Typed error details, task versioning, call interceptors, streaming wiring + doc audit

Changed

• (a2a-agents) Drop the stale ws_port config field

Documentation

• Doc-comment audit, add ROADMAP, retire stale planning docs

Feat

• (a2a-rs) Client Transport port + JSON-RPC 2.0 client + card negotiation

Refactor

• (a2a-rs) Split streaming & push out of storage adapters (Phase 4 final)

Added

• MCP server over Streamable HTTP — run_mcp_server can now serve a
  TOML-configured agent over MCP's Streamable HTTP transport (rmcp's
  StreamableHttpService on an axum router) in addition to stdio. Configure it
  via a new [features.mcp_server.http] section (McpHttpConfig: enabled,
  host, port, path); when http.enabled it takes precedence over stdio.
  DNS-rebinding protection defaults to loopback-only and is tunable via
  allowed_hosts / allowed_origins (empty allowed_hosts disables Host
  validation for proxy-fronted public binds). Enables the
  transport-streamable-http-server rmcp feature. New mcp_http_agent example
  (examples/mcp_http_agent.{rs,toml}) plus an end-to-end initialize-handshake
  and Host-allow-list integration test (tests/mcp_http_test.rs).
• AgentBuilder::with_streaming / AgentRuntime::with_streaming — attach a
  shared streaming backend so tasks/subscribe SSE streams observe the
  broadcasts a handler emits (e.g. via the TaskStatusBroadcast mixin). Pass the
  same InMemoryStreamingHandler your handler broadcasts to (clones share
  their subscriber registry); the runtime injects it into the transport via
  ConnectRpcAdapter::with_streaming_handler and logs "📡 Streaming backend
  wired into transport" when active.
• complex_agent example (examples/complex_agent.rs +
  examples/complex_agent.toml, behind --features mcp-server) — a kitchen-sink
  "Research Assistant" that wires declarative TOML config, optional LLM
  tool-calling (with a keyless, deterministic rule-based fallback), MCP tool
  consumption via McpToA2ABridge (against an in-process tool server over
  tokio::io::duplex), live SSE streaming of progress artifacts, and native A2A
  task lifecycle through the broadcast mixin.

Fixed

• Streaming through the builder reached a no-op. AgentRuntime::start_http
  built its transport with ConnectRpcAdapter::new(...), which defaults to a
  NoopStreamingHandler — so broadcasts from a builder-constructed handler never
  reached tasks/subscribe SSE clients. They now do when the streaming backend
  is supplied via with_streaming (see Added).