Adds a crash-recovery preamble that restores `final` from `.old` when a
prior swap was interrupted after rename(final, old) but before
rename(tmp, final), and always drops stale `.old`/`.importing` orphans.
Also guards the swap: if nothing new was staged into tmp (empty/missing
staging) and `final` already exists, leave it untouched instead of
swapping in an empty copy. This is required beyond the literal preamble
because the pre-existing swap logic unconditionally replaced `final`
with `tmp` regardless of whether anything was actually imported, which
would otherwise destroy a just-recovered (or any existing) copy whenever
staging is empty.
Staging is no longer forced under the library. The worker reads STAGING_ROOT
(container path, default /music/.staging) and stages per-job downloads there;
docker-compose mounts ${STAGING_DIR:-${MUSIC_DIR}/.staging} at /staging with
STAGING_ROOT=/staging. Set STAGING_DIR to a fast local disk when the library
(MUSIC_DIR) is a network share so temp download I/O stays off the share.
Safe cross-volume: import_album already assembles into a temp dir on the
library volume and swaps atomically there, so partial downloads never touch
the library and the final swap stays atomic. clear_staging_root now clears the
root's contents (mount-safe) rather than removing the root. Documented in
.env.example; new tests cover the separate-root path.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Jonathan