`sync_catalog` is a read-modify-write over a file another device also
writes: take theirs, merge, push the union. It was shaped
if let Ok(bytes) = backend.get(&RemoteId::Path(target), None).await {
which folds *every* failure into "there is no remote catalog" and carries
straight on to the upload. On a placeholder library the snapshot in
`.darkroom-derived/` is dehydrated like anything else, so the read failed
every time and each sync pushed our catalog over theirs unmerged —
taking the other device's collections and their members with it.
The same shape as the sidecar bug, and the same fix: a read that fails
for anything other than `NotFound` stops the upload and says why. An
unreadable or unopenable snapshot stops it too — "will not parse" is not
"is not there". This is what `NotFound` and `NotMaterialised` being
separate errors is *for*: one means ours is the whole truth, the other
means do not dare.
Shard downloads go through the same fetch-on-demand read. They logged
and skipped before, which on a library the client keeps dehydrated is
every shard, every pass, and a peer's thumbnails and faces silently
never arriving.
And `put` over a placeholder now replaces it rather than refusing.
Refusing was over-cautious of me: derived state lives inside the library
folder, so a folder the client had dehydrated could never be written to
again. An unconditional write replaces the whole file, so there is
nothing in the stub to keep — content first, then the placeholder, since
in a synced tree an absence is a deletion that propagates. `IfMatch`
still refuses, because a stub's validator describes the stub; `IfAbsent`
fails, because the file is there and only its content is not.
dtourolle
4168d67cfa