"record the follow-up, then amend the closed receipt" was hand-written at six
sites (three Windows-resume sites, the historical-takeover resume,
gateway_restart, channel_adoption). Two of them -- _complete_source_update's
Windows resume and channel_adoption -- amended without checking that the
run's receipt was already closed. On an open run record_followup has just
persisted the follow-up into the running record, so the amend appended a
second copy to that durable record and to latest.json (what an interrupted
run leaves behind).
update_receipt.owe_followup(update_id, step, reason) records the step and
amends the archive only once the run is closed; every site now calls it.
0b5b01ba7a