Clears the three hardening items left over from the deletion-scope audit.

Topology is re-checked before every sample rather than once per run. The
preflight was a point-in-time check while the anti-join loop can run for hours;
a replica that dropped out mid-run took its references with it, so blobs it
alone held started looking orphaned and nothing noticed. ch_client is free at
that point -- the previous sample's stream has closed. Removing both preflight
call sites now fails two tests; removing either one alone is covered by the
other, so the old M7 mutation is obsolete rather than surviving.

--useafter is quoted as a SQL string literal. It was interpolated bare, so an
operator-supplied value landed as an identifier -- the only unquoted value in
the anti-join WHERE clause. The strict xfail recorded for it flipped to XPASS
and became a real test, which is what strict xfail is for.

The image sets PYTHONUNBUFFERED=1. stdout is a pipe under Kubernetes so print()
was block-buffered, and Python's default SIGTERM handling exits without
flushing: a Job killed at activeDeadlineSeconds lost its buffered tail,
including the closing "s3gc: OK", and the dev-automation shell echoes
interleaved wrongly against it. Logger records were never affected --
StreamHandler.emit() flushes per record.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>