Library.close() now returns a promise that resolves once the work it
started has finished: an in-flight refresh with its cache write, the ML
data fetch, and running precache sweeps. The interval test could see a
refresh's new state, close, and remove the directory while the write was
still running. Every library test now awaits close(), and a new test
holds a cache write open to prove close() waits for it.
The precache test waited for its stub source to be called, but the cache
records a file only after checking it on disk, so status() could lag. It
now waits for both fills to report "done".
Model: opus-5-5
Library.open loads metadata.json and serves reads from RAM: an empty cache awaits the first refresh, an existing cache returns at once and refreshes in the background so an unreachable server never stalls open(). A background timer refreshes every refreshIntervalSeconds (default 3), diffing only changed albums via the resumable cursor+tombstone enumerators and rewriting metadata.json only when something changed. A refresh failure is invisible to reads and surfaced via status()/onProgress; a failed save keeps status().lastError set and retries until one lands, so a stale disk is never masked. No sync()/refresh()/serverReachable surface; status() and close() included.
Model: opus-4-8