v3.4.6: [safe-vibe-coding] Make the sandbox better (#69)

We want to be able to better customize the error messages returned to
the models.

This change does three things:
* Adds a 64-bit alias to ATCWD.
* Changes the interface so that instead of only two rules (modifications
and deletions), now we allow the user to specify what to do with each
rule so that we can give better error messages.
* Consider the old names for renames as also being deleted.