Tests for keeping each variant's content type in memory. A second hit
must still get the stored content type after the variant's .meta file
is deleted, whether the first came from storing the variant or from
reading it after a restart; this fails now. A variant removed by
EvictToLimit, or whose file was deleted from disk, must be a miss and
must not be served, and concurrent stores, reads and evictions run
under the race detector; these pass now and guard the change.
Model: opus-5-5
