Production scenario: operator enables lifecycle on a bucket that
already holds objects from before the policy. The worker must
discover them via the bootstrap walk (BucketBootstrapper) — there
were no meta-log events to observe because the objects predate the
rule. Without the bootstrap path, only NEW writes would ever match.
Setup: PUT 5 objects (no lifecycle config yet) + 1 out-of-prefix
survivor, backdate all, THEN set the Expiration rule, run the
worker. Every in-prefix pre-existing object must be expired; the
out-of-prefix one must remain.