The folder connector was pointed at a Nextcloud VFS tree and got three
things wrong, the first of which loses work.
**A dehydrated sidecar read as absent.** `a.drsc` does not exist when the
client has dehydrated it — only `a.drsc.nextcloud` does — so `get` missed,
`.ok()` swallowed the `NotFound`, and the sidecar writer took that for
"there is no sidecar yet" and wrote a fresh document over the existing
one. Every edit another device had put there went with it. That function's
own doc comment calls this the exact loss the format's unknown-key
preservation exists to prevent.
**A stub was catalogued as a 1-byte image**, and ARCH §9.0 measured this
machine at 121,785 placeholders against 10,267 real files — so a folder
library on a synced tree was ~92% broken rows.
**Identity changed on hydration**, so downloading a photograph looked like
a delete and an add, orphaning its thumbnail and its face rows.
Entries now carry the photograph's own name and a `materialised` flag;
`get` on a stub returns the new `RemoteError::NotMaterialised`, which is
distinct from `NotFound` precisely because the sidecar writer must treat
them differently — it fetches the sidecar and merges, or leaves the entry
queued.
Hydration is a **borrow**. `BorrowPool` records what was on disk before it
asked, so `release_all` dehydrates only what a pass brought and leaves
what the user already had. Reference counted: the thumbnail pass and the
face pass meet on the same RAW, and without counting the first to finish
dehydrates the file the second is reading. A borrow against a plain folder
or a server does nothing, so a pass written for VFS runs everywhere.
Releasing means asking the client to dehydrate and never deleting: a
deletion inside a synced tree propagates to the server and removes the
photograph from every device.
Not a second backend — the capability is per *connection*, not per type,
since the same folder hydrates only while the client runs. The convention
arrives through a detector the registry supplies, so `dr-sync-folder`
still knows nothing about any client's protocol.
ARCH §9.0a records this as an amendment: finding 3 rejected hydration
because it costs 100× a range read, and that comparison assumed a
connector was available. A folder library has none.
Correcting the previous commit: I claimed VFS placeholders could not be
downloaded. That was wrong. The desktop client exposes a socket at
$XDG_RUNTIME_DIR/Nextcloud/socket speaking newline-delimited
COMMAND:argument, and MAKE_AVAILABLE_LOCALLY:<path> does fetch the file.
Verified against client 4.0.7: a 1-byte stub became a real 2.8MB file in
2.8 seconds.
Implemented as dr-sync-nextcloud::desktop_client, deliberately optional.
Android has no desktop client, no XDG_RUNTIME_DIR socket and no
placeholders, so detect() returns None there and callers fall back to the
connector. It earns its place only because it is ~30 lines with no
dependencies: where a library already lives in a VFS folder, asking the
client to fetch beats downloading a second copy over WebDAV and leaving
the client's placeholder state inconsistent.
What this does not change: hydration is whole-file, so it suits the
original tier and never browsing. Filling a grid this way downloads the
entire library. Range extraction remains the only mechanism satisfying
FR-NC-3, and ARCH §9.0 now says so precisely.
Also fixes two real Android build failures found by cross-compiling:
- reqwest's `rustls` feature defaults to aws-lc-rs, whose aws-lc-sys
crate is C and fails under the NDK — exactly the pain D1 chose Rust
to avoid. Switched to rustls-no-provider + ring, installing the
provider in the constructor so no caller can build a client that
panics on first use.
- ring itself needs CC/AR per target; cargo-ndk sets only the linker.
Added them to the container.
87 tests passing. dr-sync-nextcloud cross-compiles for aarch64-linux-android.
dtourolle