[Feature] Use the Desktop app as a UI for an existing local T3 Code server

[Pedro-Revez-Silva]

Problem

T3 Code can run as a background service without the Desktop UI, which is useful for keeping one environment available to web and mobile clients. Opening the Desktop app on that same machine currently starts another backend instead of using the server that is already running.

That creates a second local environment with separate threads and connection settings. In my use case, the background server is the durable environment I reach remotely, while Desktop should be another client for that same environment.

Proposed behavior

For packaged Desktop launches:

• Detect a live T3 Code background service or local t3 serve process on the same machine.
• Attach securely to that server by default instead of starting a second backend.
• Keep Desktop development isolated from installed or production services.
• Continue serving the renderer bundled with the Desktop app, so its UI version is independent from the server bundle.
• Show the attached state in Settings → Connections, and leave network exposure controls with the process that owns the server.
• Let users disable attachment when they intentionally want an independent Desktop environment.

If a server is detected but secure pairing fails, Desktop should not silently start another backend. It should retry transient failures first, then offer Try Again, Start Separate Backend, Open in Browser, or Quit. The separate-backend option should use isolated state for that launch.

If an attached service restarts or changes port, Desktop should rediscover it and reconnect automatically before asking the user.

Why this shape

This keeps one machine represented by one durable T3 environment across desktop, web, and mobile while preserving an explicit escape hatch. Discovery remains local, authentication uses a short-lived process-scoped grant, development stays independent, and Desktop never takes lifecycle or network-exposure ownership away from an externally launched server.

I have a working implementation and will link the pull request here as a starting point for review.

[Pedro-Revez-Silva]

Starting implementation: #8115