assemblesignedsource task created by make_signed_source workflow fails missing signatures

Given #689 (closed) and #690 (closed), the sign task now succeeds, but the subsequent assemblesignedsource task fails. Notably, my sign task produced three debusine:signing-output artifacts. The subsequently failing assemblesignedsource task does not have any relations to input artifacts. (Why?) It produced an debusine:work-request-debug-logs artifact with two files and two artifact relations. It relates to the signing template (expected) and one of the three debusine:signing-output artifacts. Looking into the task's dynamic_data confirms that signed_ids only references one debusine:signing-output artifact where I would expect three. One of the files is the execution.log and it contains a Python traceback ending in:

debusine.tasks.assemble_signed_source.AssembleError: uefi signature of 'REDACTED' not available

Is this a result of passing too few debusine:signing-output artifacts to the assemblesignedsource task?