Converged immutable uploads spend ZKAPs without allocating storage

Client uploads file A. required_passes(A) are passed to allocate_buckets and the upload succeeds.

Time passes.

Client uploads file A again (unchanged, who knows why). required_passes(A) are passed to allocate_buckets. allocate_buckets succeeds with a response that says "I have that data already". The upload never happens. Notionally, it succeeds. Storage has not been allocated but the passes are spent, anyway.