A sandbox for the A2A protocol v1.0 with a working bridge on top of it — the same A2A interface, answered by a real coding agent over ACP instead of by a placeholder.
Three protocols meet here, and the first two are easy to confuse because both are JSON-RPC: A2A between agents, ACP down to a coding agent, and MCP back out to whoever is calling. The bridge sits between them.
Everything in these pages was checked against running code, not inferred from specifications — where behaviour and documentation disagreed, the observed behaviour is what is written down, and the disagreement is called out.
It is not production: tasks live in an InMemoryTaskStore, the A2A side runs UserBuilder.noAuthentication, and the permission classifier is a placeholder for an external channel. What it is for is watching the protocol work with nothing in the way.
bin/
ambassyctl Installs and drives both processes as services (launchd / systemd)
service/ The unit templates it renders
src/
agent.ts A2A server with a placeholder executor: environment, card, port
revisor.ts That executor's logic — text statistics and the events it publishes
parts.ts The Part/Message helpers both servers build their events out of
client.ts A2A client: discovery, streaming, resuming a task
proxy.ts Wire-tap that prints raw JSON-RPC and SSE frames
raw.sh The same protocol over bare curl
acp/
agent.ts The bridge's bootstrap: backend, handshake, card, port
executor.ts The translation: one A2A task becomes one ACP prompt turn
client.ts Adapter subprocesses, sessions, idle reaping
sandbox.ts Where a conversation may work, and who created that directory
permissions.ts The permission classifier and the fs/* handlers
log.ts Two rotating JSON Lines logs
mcp/
server.ts MCP endpoint over Streamable HTTP, bearer-guarded
a2a.ts The A2A client pool the tools call
tools.ts The four tools and how their results are shaped
auth.ts Token minting and the constant-time guard
heartbeat.ts Progress ticks derived from upstream liveness
tests/ Vitest suites mirroring src/, with fixtures in tests/helpers/Start with the Revisor in src/agent.ts if you want to see the protocol with nothing else in the way: it has no external dependencies and no model behind it, so what remains is A2A itself.