Writes 30 random 1 MB files plus 10 duplicates (40 files, 30 MB of
unique content), backs them up with a 10 MB blob_size_limit, then
restores through a counting storer that records every Get per key.
Each blob on disk must be downloaded exactly once during restore — a
re-download would mean the sweeper evicted a blob whose chunks were
still referenced by an unrestored file, and zero downloads would mean
the cache silently stopped being consulted.
The duplicates exercise the dedup path: the sweeper has to keep each
blob alive until every file (original AND duplicate) that references
any of its chunks has been restored.
sneak
d9319dc0fb