`RemoteBackend` existed from the first release and bought nothing it was
designed for. Seven files in `dr-ui` constructed a `NextcloudBackend`
directly, an account *was* a server URL beside a DAV user id, the local
cache directory was named after a hostname, and the launch screen knew
that signing in meant a browser handshake. The trait was real; the seam
was documentation.
A trait over operations is only a quarter of it. Pluggable storage needs
four things, and this adds the other three:
- **Capabilities** — already there, and the reason the engine can drive
two backends at the speed each actually runs at.
- **Configuration** — `dr_sync::Account`: where a library lives, in
whatever form its connector addresses, with no server in it. Loads
every existing config unchanged (`backend` defaults to `nextcloud`,
`endpoint` is stored under its historical `server` key), and
`Account::namespace()` reproduces the old catalog directory byte for
byte, because changing it would abandon a catalog, its thumbnail
shards, and the sidecars holding unsynced offline work.
- **Registration** — `BackendProvider` and `BackendRegistry`.
`ui/dr-ui/src/remote.rs` is now the only file above `dr-sync` that
names a connector.
`Connection` (an account plus an optional `Secret`) replaces the
credentials-and-user-id pair that was threaded through fifteen
signatures in an order that could be swapped. `Secret`'s inner string is
reachable only through `expose()` and its `Debug` prints `Secret(***)`,
so the indirect leak — a `{:?}` on anything holding one — no longer
compiles into a leak.
Nextcloud is unchanged and keeps every peculiarity: propagating ETags,
chunked upload v2, `oc:fileid`, the `oc:permissions` probe on a refused
PUT, the 423 retry classification, Login Flow v2. Those are what the
capability model exists to serve, not something to hide.
`dr-sync-folder` is the second connector: a local disk, a network mount,
an external drive, or a folder a Nextcloud client already syncs. No
account, no credential — the route that works where no secrets daemon
does. It declares `LocalEtags` rather than claiming propagation a POSIX
directory cannot provide, which costs nothing because 50k `stat` calls
are not 50k PROPFINDs. Identity is a path hash, not an inode: an inode
survives a rename but differs between devices and is reused after a
delete, so two machines would disagree about which photograph a
thumbnail belonged to. Re-deriving a thumbnail is a cost; showing the
wrong one is a bug.
docs/storage.md is the contract — the traits, the four steps to add a
backend, and what each connector declares. ARCH §8.0 and §8.4a, and
FR-NC-13, say why.
dtourolle
f12aece07e