IMPORTANT: This is a full-replace operation (PUT semantics). Every active metadata key
omitted from the request body is cleared. To set or clear individual keys without
disturbing the rest, use patch-contract-metadata instead. Null, empty, and
whitespace-only values clear a single key. Archived keys may only be cleared, never changed.
Every key must name a definition assigned to contracts: an unknown key, or one assigned
only to another entity type, fails the request with a 400. Keys are never silently
ignored. The write is atomic: if any key fails validation, nothing is written.
A matching contract "Edit or amend" approval rule holds the change: the request answers 202 with the approval request, and the
contract keeps its values until the request is approved. While another change to the contract waits for approval, the request
is refused.