0685bf1992
Main removed the live-path runtime FTS rebuild (18ac3c4fb6) and #99652
narrowed the corruption classifier, after the salvaged PR #89364 branched.
Update its tests to assert the current contract: no fail-open detach on a
replaced file (fts_enabled stays True, no stale marker), fail-open (not
rebuild) for genuine same-file FTS corruption, and FTS-provenance errors
for the guard probe since generic malformed no longer reaches fail-open.