rsync forwards --mkpath to the remote side when sending, so a remote
rsync older than 3.2.3 (notably stock macOS, whose openrsync is
"rsync 2.6.9 compatible") rejects every sync with "unrecognized
option '--mkpath'".

rsync creates the final component of the destination path on its own,
so flat remote paths keep working everywhere, including the documented
rrsync setup whose root is pre-created. Only a nested remote path with
missing parents now needs a one-time mkdir -p on the server; the log
shows rsync's error when it is missing.

Reported-by: jsvk
Link: https://codeberg.org/0xlena/rsend/pulls/1

The containment check was a bare prefix match, so a sibling such as
/storage/emulated/0-evil passed for a root of /storage/emulated/0.

A crash mid-write corrupted config.json, and every later load then
threw on parse, crash-looping the app until its data was cleared,
losing the key and pinned host. Write to a temp file and rename.

A stopped worker (schedule replaced, constraints lost) left rsync
running detached until its own network timeout, including a window
where a WiFi-only sync kept pushing on another network. A watchdog
coroutine destroys the process on cancellation, which also closes its
pipes and unblocks the log reader; the worker rethrows cancellation
instead of logging it as a folder error.

The trailing-slash fix-up turns an empty local path into /, so a blank
folder row would rsync the entire filesystem; an empty remote path
pushes into the rrsync root. Reject both when saving a folder, skip and
log them at run time in case the config was edited by hand, and log why
a sync was skipped when the app is not configured yet.

rsh -keygen printed the pubkey but wrote the key pair into a directory,
so generating a key briefly left the plaintext private key on flash,
contradicting the documented invariant that it only ever exists in
memory. -keygen now emits the private key PEM on stdout and nothing
else; the app encrypts it immediately and derives the public key via
-pubkey, reusing the validated import path. Keygen failures now surface
as an error dialog instead of crashing the app from a bare thread.

Typing absolute paths is error-prone; let the user browse real
filesystem folders and pick one. Stays on real paths (no SAF) so
rsync keeps operating on POSIX paths.

A small Android app for one-way folder backup, a KISS alternative to
Syncthing. It bundles rsync (built from pinned source via the NDK) and
a pure-Go SSH transport, both shipped in the APK as lib*.so and run from
the native library directory.

rsend pins the host key, stores the ed25519 identity Keystore-encrypted,
pushes each folder additively or as a mirror, and runs on demand or on a
WiFi-only schedule. The build is self-contained and reproducible: make
setup provisions the toolchain, make builds rsync, rsh, and the APK.