Restores original callback (hardcoded False), pretty_status_message refactor, umask pattern, known_inits name, unguarded operations access, and inline subst_locale — all of which were changed in earlier CodeQL fix commits. Keeps only harmless changes: unused import removal (sys, re), PEP8 comma space, and _change_mode zero-division guard. Adds large ASCII warning header: DO NOT EDIT without full ISO test.