Closing a stream in the parallel chunked reader cancels the stream's
context, so the in-flight read returns context.Canceled. This was wrapped
and returned as "failed to read stream", which the VFS cache downloader
treats as a real download error - it only recognises
asyncreader.ErrorStreamAbandoned as a benign teardown, as returned by the
sequential reader.
Return asyncreader.ErrorStreamAbandoned for a cancellation so tearing down
the parallel reader (on close, seek or reposition) is recognised as benign,
matching the sequential reader, instead of logging download errors and
retrying when --vfs-read-chunk-streams is used with --vfs-cache-mode full.
Nick Craig-Wood
ed9eec0f20