Implement alert instruction whitespace normalization

internal/forecast/derive.go

@@ -492,7 +492,7 @@ func parseAlert(raw json.RawMessage) (parsedAlert, bool) {
 		Headline:    firstStringField(fields, "headline", "title"),
 		Severity:    stringField(fields, "severity"),
 		Description: stringField(fields, "description"),
-		Instruction: stringField(fields, "instruction"),
+		Instruction: collapseWhitespace(stringField(fields, "instruction")),
 	}
 	start, startOK := firstTimeField(fields, "onset", "startsAt", "startTime", "effective", "sent")
 	end, endOK := firstTimeField(fields, "ends", "endsAt", "endTime", "expires")
@@ -542,6 +542,10 @@ func firstTimeField(fields map[string]json.RawMessage, names ...string) (time.Ti
 	return time.Time{}, false
 }
 
+func collapseWhitespace(value string) string {
+	return strings.Join(strings.Fields(value), " ")
+}
+
 func intersect(left timeutil.Period, right timeutil.Period) timeutil.Period {
 	start := left.Start
 	if right.Start.After(start) {

internal/forecast/derive_test.go

@@ -211,7 +211,7 @@ func TestAlertOverlap(t *testing.T) {
 }
 
 func TestAlertOverlapUsesOnsetAndEnds(t *testing.T) {
-	raw := json.RawMessage(`{"event":"Wind Advisory","headline":"Wind Advisory issued June 16 at 12:39PM CDT until June 17 at 8:00PM CDT by NWS St Louis MO","severity":"Moderate","description":"Southwest winds 20 to 30 mph with gusts up to 45 mph expected.","instruction":"Secure outdoor objects.","effective":"2026-06-16T17:39:00Z","onset":"2026-06-17T18:00:00Z","ends":"2026-06-18T01:00:00Z","expires":"2026-06-17T08:45:00Z"}`)
+	raw := json.RawMessage(`{"event":"Wind Advisory","headline":"Wind Advisory issued June 16 at 12:39PM CDT until June 17 at 8:00PM CDT by NWS St Louis MO","severity":"Moderate","description":"Southwest winds 20 to 30 mph with gusts up to 45 mph expected.","instruction":"Secure outdoor objects.\n\nUse  extra\tcaution.","effective":"2026-06-16T17:39:00Z","onset":"2026-06-17T18:00:00Z","ends":"2026-06-18T01:00:00Z","expires":"2026-06-17T08:45:00Z"}`)
 	alertRun := &weatherdata.AlertRun{Alerts: []json.RawMessage{raw}}
 	period := timeutil.Period{
 		Start: mustParse("2026-06-17T12:00:00-05:00"),
@@ -237,11 +237,34 @@ func TestAlertOverlapUsesOnsetAndEnds(t *testing.T) {
 	if overlaps[0].Description != "Southwest winds 20 to 30 mph with gusts up to 45 mph expected." {
 		t.Fatalf("Description = %q, want preserved description", overlaps[0].Description)
 	}
-	if overlaps[0].Instruction != "Secure outdoor objects." {
+	if overlaps[0].Instruction != "Secure outdoor objects. Use extra caution." {
 		t.Fatalf("Instruction = %q, want preserved instruction", overlaps[0].Instruction)
 	}
 }
 
+func TestCollapseWhitespace(t *testing.T) {
+	tests := []struct {
+		name  string
+		value string
+		want  string
+	}{
+		{name: "newlines", value: "Secure outdoor objects.\nUse extra caution.", want: "Secure outdoor objects. Use extra caution."},
+		{name: "crlf", value: "Secure outdoor objects.\r\nUse extra caution.", want: "Secure outdoor objects. Use extra caution."},
+		{name: "tabs and repeated spaces", value: "Secure\toutdoor   objects.", want: "Secure outdoor objects."},
+		{name: "leading trailing", value: "  Secure outdoor objects.  ", want: "Secure outdoor objects."},
+		{name: "empty", value: "", want: ""},
+		{name: "all whitespace", value: " \n\t\r\n ", want: ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := collapseWhitespace(tt.value); got != tt.want {
+				t.Fatalf("collapseWhitespace(%q) = %q, want %q", tt.value, got, tt.want)
+			}
+		})
+	}
+}
+
 func TestAlertOverlapUsesOnsetAndEndsForLocalDateRelevance(t *testing.T) {
 	location, err := time.LoadLocation("America/Chicago")
 	if err != nil {