When a sandbox is destroyed and we provision a fresh one for the same
task, the agent may have previously committed and pushed onto the
feature branch. The previous prepare scripts only ran `git checkout -b
{{worktree.branch}}` which would overwrite that progress with a fresh
branch off the chosen base.
Try `git fetch origin <feature>` first; on success, `git checkout -B`
against the remote tip so the agent picks up where it left off. Falls
back to a fresh local branch when origin has nothing.
Also add the same checkout block to the Sprites prepare script — it was
missing entirely, so every Sprites session was committing onto main.
José Almeida