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.
A general alert rule with Duration:0 (accepted by the API, no minimum
validation) drove fail*100/total with total==0, panicking with an integer
divide-by-zero inside checkStatus, which has no recover and would take down the
whole alert goroutine — a config-reachable DoS by any user able to create alert
rules. Skip duration<=0 rules in Check via continue (not boundCheck, which would
pollute hasPassedRule and skip sibling valid rules). Also trim the sample slice
when max<=0 in alertsentinel, otherwise it appended every tick without ever
trimming. Adds regression tests for zero-only and mixed rule sets.
naiba
UUBulb