Fork a thread to another connected machine

[adamblumoff]

Auto balance is great most of the time, but it started one of my threads on a machine I didn't mean to use, and there was no easy way to undo that. Moving it to the right computer felt like too much work, so I had the agent SSH into the other machine and set things up there itself. That took a lot longer than it should have.

I'd like a "Fork to…" action that starts a new thread on another connected machine with the same context. It would fix a thread that landed on the wrong machine, and it would make it easy to split work, like keeping a thread going on one machine while a fork picks up a related task on another.

The original thread keeps running and git stays where it is. If the branch has unpushed changes, T3 could warn before forking.

Unlike #6874 and the earlier PRs that tried to move a thread between machines, this doesn't move anything. It starts a new linked thread and leaves the original where it is.

Related: #6874, #7838