Walkthrough: an A2A repeater service

Goal: a client's chatbot only has its own HTTP API. Put it behind the A2A protocol with a service plugin, then add it to wick as a remote agent — without changing wick.

The working reference is plugins/service/example_a2a_repeater in the wick repo (its "bot" is simulated in-process; a real one calls the client's API).

1. Read the bot API

Note three things from the client's documentation:

• how to open a conversation (and the id it returns),
• how to send a user message and get the reply (sync, poll, or stream),
• the credentials it needs.

2. Write the adapter

service/a2a_botx/
├── main.go     service.ServeService(Module())
└── VERSION     0.1.0

• Configs: base URL + API key (secret → encrypted by wick, edited on the plugin's admin page).
• Routes:
  • /.well-known/agent.json → service.Public (the agent card),
  • / → service.Token for JSON-RPC (message/send, message/stream). (The example registers a single / route as service.Public to keep the demo short; use service.Token for the JSON-RPC route in production.)
• Register: serve the agent card and the JSON-RPC endpoint. Keep a map A2A contextId → bot conversation id; create the conversation on the first message of a context.
• message/stream answers with SSE; the host flushes each event, so stream as the bot replies.
• Optional: implement RemoteSource to offer the same bot directly as a Team remote source.

3. Build and install

wick plugin build --kind service a2a_botx --target linux/amd64
<app> plugin install bin/a2a_botx-0.1.0-linux-amd64.zip

Then on Manager → Services → a2a_botx: fill the config, generate the access token, and check the status is running.

4. Check it

curl https://<wick>/x/a2a_botx/.well-known/agent.json
curl -H "Authorization: Bearer <token>" -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"message/send","params":{"message":{"role":"user","parts":[{"kind":"text","text":"hi"}],"messageId":"m1"}}}' \
  https://<wick>/x/a2a_botx/

Any A2A client (for example a2a-go) can now talk to it.

5. Use it from Team

Either add an A2A remote agent pointing at https://<wick>/x/a2a_botx/.well-known/agent.json with the token, or — when the plugin implements RemoteSource — pick source Plugin in the Remote agent wizard. The agent can be exposed again through the A2A/REST connection like any other agent.