SetMetricHooks (0%→100%):
- Sets all four hooks correctly
- Nil hooks are safely handled
- Properly saves/restores state to avoid test pollution
NotifyExistingAlert (0%→100%):
- Non-existent alert is no-op
- Existing alert dispatches async notification
GetResolvedAlert (0%→100%):
- Returns nil for non-existent alert
- Returns nil for nil resolved entry
- Returns nil when Alert is nil
- Returns cloned alert with resolved time
GetAlertHistory/GetAlertHistorySince (0%→100%):
- Returns history from history manager
- Respects limit parameter
- Zero time returns all history
- Filters by time correctly
ClearAlertHistory (0%→100%):
- Clears all history entries
Coverage: 56.9% → 57.4%
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