`dr-sync` defines `RemoteBackend` and a capability model the engine adapts
to, so a second backend can be added without touching the code that uses
one. That boundary was documentation. Seven files in `dr-ui` constructed a
`NextcloudBackend` directly, ten functions took one by concrete type, and
exactly two call sites in the tree — both inside `dr-sync` itself — ever held
the trait object. A WebDAV or local-folder backend would have had a
well-written trait to implement and nowhere to go afterwards.
The change is smaller than the finding suggests, because the trait was
already right. Every method the UI has ever called on a backend — `get`,
`put`, `list`, `delete`, `create_dir`, `move_to` — was already on it, so
nothing had to be added and no behaviour moved. Ten signatures widened to
`&dyn RemoteBackend`, sixteen constructions became `remote::connect`, and
`remote.rs` is now the only file in the interface that names a connector.
`connect` returns `Result<Box<dyn RemoteBackend>, RemoteError>`. The error
type is `dr-sync`'s rather than the connector's, which is why every call site
kept its shape — the `match`, the `let Ok(..) else`, and
`.map_err(ScanFailure::local)?` all still read as they did.
One wrinkle worth recording: `&Box<dyn Trait>` does not reach `&dyn Trait` on
its own. The compiler reaches for unsizing, which wants
`Box<dyn RemoteBackend>: RemoteBackend`, and reports a confusing missing impl
rather than suggesting a deref. Twelve call sites therefore say `&*backend`,
and two say `let backend: &dyn RemoteBackend = &*backend` where a borrow is
shared across lanes.
What this does *not* do is abstract credentials. `AppCredentials` is an app
password from Login Flow v2 — a Nextcloud protocol, not a general notion of
authenticating to a remote — and seven files still name it. An OAuth token, a
bucket key pair and an app password have no useful common shape, so deciding
what an account is across backends before a second one exists would be a
confident guess. code-health.md CH-2 now records that as the remaining half,
and it should wait for the backend that forces it.
Verified: fmt clean, clippy clean at -D warnings, 2041 tests pass.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
An audit of code quality and extensibility, written because the answer to
"how hard is it to add a feature here?" splits cleanly in two and the split
is not where it looks.
The develop pipeline is genuinely open: a new operation is one file in
`ops/`, and the claim that no code in `ui/` names an operation turns out to
be true — all fifteen ids grepped across every .rs and .slint file in `ui/`
yield one hit, a localisation test. `dr-ui` is the opposite: every feature
lands in `run()`, one of the `wire()` functions, and a root component
carrying 472 members, so contributors collide by construction.
Five findings, CH-1 to CH-5, each with a falsifiable "done when" in the
idiom technical-debt.md already uses. The distinction from that document is
deliberate and stated: it records compromises that were chosen and are
load-bearing until their criterion is met; this records friction nobody
chose. A section listing what must NOT be tidied comes before the findings
for the same reason.
CH-1 is not a new diagnosis. view-composition.md specified the fix on
2026-08-09, when `run()` was 500 lines; it is 1,810 now, the two view
booleans it described are five, and the conditional chains it predicted in
app.slint are five-term conjunctions. The entry references that spec rather
than restating it, and quantifies the cost of the delay.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
dtourolleandClaude Opus 5