Smith::Checkpoints

Snapshots of the files a run is about to change, so a run can be taken back.

smith may write and edit files. Without this the only way back is git, which only helps if you happened to commit first — rarely true mid-session. The point is to lower the cost of letting smith write at all, and with it the pressure to leave --yes on out of convenience.

bash is deliberately not covered. What a shell command touches is not predictable, and a rewind that claims more than it delivers is worse than none. That limit is stated in the output and in the README.