A non-versioned metadata-only self-copy (CopyObject with source == destination
and the REPLACE directive) is a read-modify-write of one entry, which is why it
held the distributed lock. It now routes to the owner as a serialized
PATCH_EXTENDED: the owner merges the new managed metadata (set the replacements,
delete the dropped keys) onto a fresh read of the entry under its per-path lock,
so a concurrent change to non-managed keys (legal hold, retention, version id) is
preserved instead of clobbered, and bumps mtime.
PATCH_EXTENDED gains touch_mtime for the mtime bump. Versioned and suspended
self-copies create a new version (already routed via the copy finalize) and the
no-owner bootstrap keep the lock.