One host, several devices: how to avoid duplicate agent replies (one server per data directory)

[caitlon]

Symptom. A Mac at home hosts T3 Code; a laptop and a phone connect to it. Messages sometimes get two answers, two agents edit the same files, or a thread says another session is running. Cause: two or more T3 servers serve the same ~/.t3 data directory, and each starts its own agent for the thread (#14115).

How several servers end up on one host. Any two of these at once:

• the background service (t3 service install, or npx t3 connect offering it);
• the desktop app on the host itself with Local environment on (it runs an embedded server);
• a laptop connected to the host as an SSH environment, which launches its own t3 serve there (and, on 0.0.45, restarts it on every reconnect, SSH remote: client kills its own managed server on every reconnect (default-runtime adoption check) #15986).

Setup that keeps exactly one server.

1. On the host, keep only the background service: t3 service install (or accept it during npx t3 connect), check with t3 service status.
2. In the desktop app on the host: Settings → Connections → turn Local environment off and T3 Connect off for this machine, then add the host's T3 Connect environment under Environments. The app becomes a client of the service and can be quit freely.
3. On the laptop and phone: connect to the host through T3 Connect only; remove any SSH environment pointing at the same host.

Check. On the host, lsof -nP -iTCP -sTCP:LISTEN | grep -i t3 should list a single t3 listener and no T3 Code one. Two listeners mean two servers.

Caveat. Don't unload or restart the service while devices are connected; that cuts them off until it is back.