Arvados

Rather than require the client to detect different types of signatures and do an extra step, we could make the "create/update collection" APIs do all the necessary copying when given remote signatures.

(A "refresh local signatures" API would be "create expiring collection" under the hood anyway. The typical use case is "ensure all signatures are local; save manifest to a collection" so we might as well skip the temporary collection and go straight to saving the real one.)

Whatever "operation in progress" mechanism we use should be done such that any API can use it, and client libraries can implement it generically. E.g., send an "I understand 202" header, and follow up transparently, so the application doesn't need to care which operations involve multiple HTTP requests.