Hojun-Cho
cdc8bda721
Same contract as the 27 repaired byte/artifact survivors: checked acquisition, one all-exit cleanup funnel per carrier, ENOENT-tolerant checked unlinks, exact-path deletion, and cleanup failure fails a passing carrier without overwriting its diagnostic. Also closes the vacuous-green channels: empty-artifact pairs no longer byte-compare equal, capture and staging failures fail their row loudly, 950 requires a clean checker exit on no-error rows and hard-fails on a missing wwdump_ww, 992 keys its scratch per invocation so a failed cleanup cannot leak stale objects into the next tool's compare, and 995 no longer pre-sweeps a workdir it never created. No assertion is weakened; 990_selfhost is retired in the next commit rather than repaired.