Trim alert samples using AlertRule.RetentionWindow() (max rule duration)
instead of Check()'s verdict max, which is 0 while a rule's window is still
filling. The old max<=0 trim wiped history every tick, so Duration>=2 general
rules never accumulated enough samples and never fired a notification.
Add model + end-to-end singleton regression tests covering sample
accumulation, the retention-window contract, and the actual notify path.
naiba
e756b4540c