remove_job() deletes <cron>/output/<job_id>/ together with the record, but the
finishing run then called save_job_output(), re-creating the directory and
writing the final run into it. Every self-removing job leaked an orphan
directory the store no longer knew about, and the docs claim that "only the
job record is gone afterwards" was false. Skip the save when
self_removal_delivery_allowed() is true (the same check that already excuses
the missing record on the delivery and mark paths); delivery composes without
an output_file, as it already does for non-file paths.
The BaseException handler in _run_one_job_body still called mark_job_run on
the missing record after a self-removal crash. Guard it with the same check so
the crash path matches the completion path instead of probing a deleted record.
Docs: state that the record and its output directory are both gone.
Review finding: self-removed run re-creates the rmtree'd output dir (orphan leak); crash path marks a missing record.
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