- Check free space before downloading (only the not-yet-fetched bytes) and, on
Android O+, use StorageManager.getAllocatableBytes/allocateBytes so the system
can evict its cache; fail fast with a clear message instead of dying mid-write.
SessionInstaller sets a SessionParams size hint so staging can reserve space
too.
- Verify each APK at most once: files already verified during the download pass
are skipped in the final verification gate. Prefer SHA-256 and log SHA-1
fallback.
- An expired download URL (403/410) now clears the stored file lists and retries,
re-purchasing fresh URLs instead of repeatedly failing on the dead one.
- Cancel promptly mid-file rather than only between files, and cancel copyTo's
progress timer in a finally to avoid leaking the timer thread.
- Download.canInstall now requires a real .apk on disk; DownloadStatus
finished/running are Sets.
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