Add Mattermost Channel

Adds Mattermost DMs, channels, threads, files, reactions, and interactive approval cards. Messages arrive over Mattermost's WebSocket; card clicks return to NanoClaw over an authenticated HTTP callback. Every step is safe to re-run.

Discover the server first

Do this before installing the adapter or asking for a URL. The goal is to reuse a healthy Mattermost the user already has and establish one canonical base URL.

1. Check an existing MATTERMOST_BASE_URL in the current environment and NanoClaw env/config files. Do not print tokens or dump whole env files.
2. Probe likely local URLs, at least http://localhost:8065 and http://127.0.0.1:8065, using GET /api/v4/system/ping. A listening port alone is not evidence that the service is Mattermost.
3. Inspect Docker/Compose for Mattermost containers. If a matching container exists but is stopped, offer to start it with its original mechanism; do not start or recreate it without the user's approval.
4. If you find a healthy server, show its URL and ask the user to use it or enter a different URL. Do not select a server automatically. Treat the localhost and 127.0.0.1 endpoints for the same container as one server.
5. If nothing healthy is found, offer Mattermost's maintained evaluation and deployment guidance from SERVER_SETUP.md, then ask for the server URL after the operator has one running.

Set MATTERMOST_BASE_URL to the chosen canonical URL (scheme included, no trailing slash), then use that exact hostname in browser/Desktop setup. NanoClaw connects to Mattermost; it does not install or manage the server.

Apply

1. Detect or select the server

Test the configured URL and the standard local URLs. A detected server is only a suggestion. The user must select it.