Starting a new prompt on an existing autopilot branch should only target that branch

[chanakyav]

I ran autopilot start --prompt "We have some merge conflicts from master, we need to update our branch with the new changes. Fix any merge conflicts" on an autopilot created branch.

Maybe my prompt wasn't correct, it created an entirely new branch and tried to do weird stuff.

If we are already on an autopilot/<task-id> branch, we should just lock our changes to that branch.