- _buildDownloadRequestPayload/_historyItemFromResult shared by the
inline and native-worker paths; _buildOutputDir now derives from
_buildRelativeOutputDir
- shouldAbortWork extended (deleteFileOnAbort, null-item check) and
used at all ten guard sites; _purgeAlbumRgEntry replaces six copies
- ProgressStreamPoller shared by download queue and local library;
openVerificationAndAwaitGrant shared by queue and track provider
