* preserve compression state during replication
* explain why ParseUpload skips compression for replica writes
* fix data race on err result in FetchAndWriteNeedle
The local-write and replica-write goroutines all wrote the named err return under an unsynchronized err==nil check. Give each goroutine its own error slot and combine after wg.Wait(): local error wins, then the first replica failure.
* skip redundant decompression of compressed needles during replication
doUploadData decompressed a compressed input only to report the clear-data length on UploadResult.Size, which both replication callers discard. Skip the decompress when IsReplication.
Chris Lu
94357ac6a9