Validate hourly forecast time bounds

internal/weatherdata/bundle.go

@@ -132,6 +132,11 @@ type ForecastPeriod struct {
 	RelativeHumidityPercent           *float64  `json:"relativeHumidityPercent,omitempty"`
 }
 
+// HasUsableTimeBounds reports whether the period has a non-empty time range.
+func (p ForecastPeriod) HasUsableTimeBounds() bool {
+	return !p.StartTime.IsZero() && !p.EndTime.IsZero() && p.EndTime.After(p.StartTime)
+}
+
 type AlertRun struct {
 	AsOf   *time.Time        `json:"asOf,omitempty"`
 	Alerts []json.RawMessage `json:"alerts,omitempty"`

internal/weatherdata/bundle_test.go

@@ -69,6 +69,30 @@ func TestConvectiveOutlookRunJSONPreservesGeometry(t *testing.T) {
 	}
 }
 
+func TestForecastPeriodHasUsableTimeBounds(t *testing.T) {
+	start := mustParseBundleTime("2026-05-29T13:00:00Z")
+	end := mustParseBundleTime("2026-05-29T14:00:00Z")
+	tests := []struct {
+		name   string
+		period ForecastPeriod
+		want   bool
+	}{
+		{name: "valid", period: ForecastPeriod{StartTime: start, EndTime: end}, want: true},
+		{name: "missing start", period: ForecastPeriod{EndTime: end}},
+		{name: "missing end", period: ForecastPeriod{StartTime: start}},
+		{name: "empty range", period: ForecastPeriod{StartTime: start, EndTime: start}},
+		{name: "reversed range", period: ForecastPeriod{StartTime: end, EndTime: start}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := tt.period.HasUsableTimeBounds(); got != tt.want {
+				t.Fatalf("HasUsableTimeBounds() = %t, want %t", got, tt.want)
+			}
+		})
+	}
+}
+
 func mustParseBundleTime(value string) time.Time {
 	parsed, err := time.Parse(time.RFC3339, value)
 	if err != nil {