completeMultipartUpload routes its writes to the object's owner filer when an
owner is known, off the distributed lock. Idempotent replay is handled
gateway-side in prepareMultipartCompletionState (it returns the existing result
when the object already carries this UploadId), so the lock is not needed to
dedupe retries; with no owner yet, the lock remains as the bootstrap path.
Versioned completion flips the .versions pointer via routedVersionedFinalize
(RECOMPUTE_LATEST). Non-versioned and suspended completion write the object via
routedMkFile (a routed PUT) so the write serializes with concurrent writes to
the same key on the owner's per-path lock. The version file itself is a unique
path and stays a plain mkFile.
Chris Lu
eeda7181aa