v1.4.0 to v1.5.0

---

name: a2a

description: Agent-to-Agent protocol bridge for Ouroboros. Provides a local A2A-compatible server plus client tools for discovering and messaging other A2A agents.

type: extension

entry: plugin.py

plugin_api: "2.0"

runtime: python3

env_from_settings: []

when_to_use: User asks to communicate with another A2A-compatible agent, discover an agent card, send an A2A message, check A2A task status, or expose this Ouroboros instance as an A2A peer.

timeout_sec: 120

install_specs:

- kind: pip

package: "protobuf<6"

- kind: pip

package: "a2a-sdk[http-server]>=1.0.0,<2.0.0"

companion_processes:

- name: a2a_server

command: [python3, scripts/a2a_daemon.py]

runtime: python3

restart_policy: on_failure

---

# A2A skill

Note for reviewers: the companion daemon is declared in this manifest's

frontmatter under `companion_processes` (name `a2a_server`, argv

`[python3, scripts/a2a_daemon.py]`, runtime `python3`, restart policy

`on_failure`) and is registered at load via

`api.register_companion_process("a2a_server")`. The host's extension

loader resolves the descriptor from the frontmatter; review-prompt

manifest summaries may omit the `companion_processes` field, so consult

the frontmatter above for the authoritative declaration.

This skill moves Ouroboros's Agent-to-Agent protocol support out of the

core runtime. It exposes a small local A2A-compatible JSON-RPC server and

registers three client tools:

- `discover` — fetch another agent's Agent Card.

- `send` — send a message to another A2A agent.

- `status` — check a remote task status.

The companion process talks back to the host through the loopback Host

Service API using the reviewed `SkillToken` grant. It does not patch the

core runtime and stores task state under the skill state directory.

## Outbound peer credentials

The client tools (`discover`, `send`, `status`) send HTTP Basic credentials only

to ONE explicitly configured peer. Set both `A2A_CLIENT_PASSWORD` and

`A2A_CLIENT_PEER_URL`; the credential is attached only when the target URL's

origin (scheme, host, port) exactly matches that configured origin, and every

other peer is contacted anonymously. This is deliberate: the tools accept an

arbitrary caller-supplied URL, so a process-wide credential would be handed to

whatever address the model happened to pass.

## Agent card

The published Agent Card describes what this Ouroboros instance actually

does, capability-first. The top-level name is the stable product name

`Ouroboros` (operator-set `A2A_AGENT_NAME` wins when configured — the host

`/identity` name is deliberately NOT used: it is the identity document's

first heading, a section title like "Who I Am", not an agent name). The

description leads with a curated capability summary and appends the host

`/identity` first line as flavor (`A2A_AGENT_DESCRIPTION` overrides the

whole field). The skill list always begins with five curated capability

categories (code and files, web and media, long-running tasks and

projects, self-modification, skills), followed by live per-tool entries

from the host tool schemas (`GET /tools/schemas`). A discovery GET answers

in seconds: the request path uses the last known-good tool list and a

short fetch only, while a background refresher owns the long host-warmup

retry ladder and keeps the list warm. When the tool registry is genuinely

unavailable the card still carries the curated categories — it never

collapses to a contentless "General" stub nor to an identity-persona-only

entry.