@onlyworlds/sdk 4.9.0

Added

• Only if unchanged (keel #210). patch(type, id, partial, { ifMatch }) and
  editLinks(type, id, field, edit, { ifMatch }) send If-Match: "<change_seq>": the write
  lands only if the element is still at that change_seq. When it has moved, nothing is
  written and the call throws OwPreconditionFailedError (412 precondition_failed), an
  OwApiError whose current is the element as it is now, so the client's re-read is free.
  OwApiError.isPreconditionFailed names the case. The server never merges; the client
  compares the copy it edited from with current. An ifMatch that is not a whole number
  throws TypeError before anything is sent. Without ifMatch, nothing changes.
  Checked live on keel-staging: a matching token lands, a stale one is refused with
  current at the live change_seq, the refused write changes nothing, and the links
  route behaves the same.