upload_files: a failed complete_workunit discards the UploadSummary of a successful upload

[Caushi]

Problem

When every transfer has succeeded but the final status flip fails, upload_files raises and the caller loses the UploadSummary — so it never learns which files actually landed, or the workunit id.

operations/workunit/upload.py:277:

elif created:
    # Intentionally outside the try/except above: the bytes have already landed, so a failure of
    # this final status flip should surface as-is rather than mark a workunit-with-real-content
    # 'failed'. It stays 'processing' and the exception propagates for the caller to retry.
    _ = complete_workunit(client=client, workunit_id=workunit_id)

Not marking the workunit failed is right, and the comment explains why. The problem is only that the raise is bare: the summary describing a successful upload is discarded along with it.

Observed consequence

Hit while testing BioBeamer's tus backend. A run uploaded both groups' bytes successfully; the second group's complete_workunit then failed:

14:23:58  group 1 -> workunit 346730, 2 uploaded
14:24:04  group 2 -> Query was not successful: Invalid or expired token.

(The token error was our own fault — the local B-Fabric's OAuth issuer had been switched from fgcz-test to localhost mid-session, so the JWT was valid but for the wrong issuer. Not a bfabricpy bug. The summary loss is the point here.)

Because the exception carried nothing, the retry had no way to know those files were already stored. It created a second workunit (346732) linking to the first one's bytes — a duplicate workunit for one acquisition. The bytes were fine either way; the bookkeeping was not.

Worth noting the storage service's post-finish hook had already set the resources and workunit to AVAILABLE, so complete_workunit may be partly redundant on the tus path — possibly worth confirming with the storage-service side whether it needs to run at all there.

Suggested fix

Attach the completed summary to the exception, e.g.:

class WorkunitCompletionError(BfabricTransferError):
    """The upload finished but the workunit's final status flip failed."""
    def __init__(self, message, summary: UploadSummary): ...

Behaviour otherwise unchanged: still raises, still leaves the workunit processing, still does not mark it failed. But a caller can then record what transferred and retry only the status flip instead of re-uploading or creating a second workunit.

For reference, BioBeamer needed the same shape one level up and solved it the same way (TusUploadFailed carrying files_copied), so that partial successes still reach the copied-files ledger before the run fails.