introduce two distinct warmup_spam_reports report types:
- spam_placement: provider classifier put the message in Junk on arrival
- user_complaint: recipient explicitly flagged the warmup message
detect placement at warmup arrival via the incoming message flags and
record it through a new WarmupService.RecordSpamPlacement. evaluate the
two signals independently in the health sweep — user complaints now
have their own watch/quarantine/block thresholds (0.5 / 1.5 / 3.0%)
since they are a stronger negative signal per event than placement.
Matthew Meszaros
4fb5885130