File rows are shared by every snapshot and updated in place, while a
blob row is deleted once no snapshot references it. Removing the newest
snapshot, or the prune after an interrupted run, could drop the only
blob holding a changed file's current chunks while an older snapshot
kept the file row. The next backup compared metadata only, skipped the
file, and completed a snapshot that could not restore it.
The scanner now loads the IDs of known files that list a chunk no
uploaded blob holds and re-chunks them even when their metadata is
unchanged.
The tests append to a file, so the file keeps its first chunk in a blob
the first snapshot still references. Each backup run gets its own
snapshot name, so the second-precision snapshot IDs differ without
sleeping.
Model: opus-5-5
sneak