Validate precipitation probabilities and ice wording

internal/facts/facts.go

@@ -101,6 +101,11 @@ func BuildDerived(req BuildDerivedRequest) (DerivedFacts, error) {
 	}
 	bundle := req.Collected.Bundle()
 	period := req.Resolved.ValidPeriod
+	if req.Collected.Hourly != nil {
+		if err := forecast.ValidatePrecipitationProbabilities(req.Collected.Hourly.Periods); err != nil {
+			return DerivedFacts{}, err
+		}
+	}
 	spcOutlooks, spcDiscussions := selectSPCConvectiveOutlooks(req.Collected.SPCConvectiveOutlooks, period)
 	derived := DerivedFacts{
 		ValidPeriodHourlyPeriods:    forecast.SelectHourlyPeriods(req.Collected.Hourly, period),

internal/facts/facts_test.go

@@ -127,6 +127,21 @@ func TestBuildDerivedDailyIncludesNextDayOvernightAlerts(t *testing.T) {
 	}
 }
 
+func TestBuildDerivedRejectsInvalidPrecipitationProbability(t *testing.T) {
+	location := testLocation()
+	bundle := testBundle(location)
+	invalid := -1.0
+	bundle.Hourly.Periods[0].ProbabilityOfPrecipitationPercent = &invalid
+	_, err := BuildDerived(BuildDerivedRequest{
+		Resolved:  resolveForTest(t, report.Hourly, mustParse("2026-05-29T08:00:00-05:00"), location),
+		Timezone:  location.String(),
+		Collected: BuildCollected(bundle),
+	})
+	if err == nil || !strings.Contains(err.Error(), "invalid precipitation probability") {
+		t.Fatalf("BuildDerived() error = %v, want invalid precipitation probability", err)
+	}
+}
+
 func TestBuildDerivedTomorrow(t *testing.T) {
 	location := testLocation()
 	for _, id := range []report.ID{report.Tomorrow} {