fix(charts): unify timeline labels across graphs

audit/internal/webui/server.go

@@ -72,29 +72,36 @@ func (r *metricsRing) snapshot() ([]float64, []string) {
 	defer r.mu.Unlock()
 	v := make([]float64, len(r.vals))
 	copy(v, r.vals)
-	now := time.Now()
 	labels := make([]string, len(r.times))
+	if len(r.times) == 0 {
+		return v, labels
+	}
+	sameDay := timestampsSameLocalDay(r.times)
 	for i, t := range r.times {
-		labels[i] = relAgeLabel(now.Sub(t))
+		labels[i] = formatTimelineLabel(t.Local(), sameDay)
 	}
 	return v, labels
 }
 
-func relAgeLabel(age time.Duration) string {
-	if age <= 0 {
-		return "0"
+func timestampsSameLocalDay(times []time.Time) bool {
+	if len(times) == 0 {
+		return true
 	}
-	if age < time.Hour {
-		m := int(age.Minutes())
-		if m == 0 {
-			return "-1m"
+	first := times[0].Local()
+	for _, t := range times[1:] {
+		local := t.Local()
+		if local.Year() != first.Year() || local.YearDay() != first.YearDay() {
+			return false
 		}
-		return fmt.Sprintf("-%dm", m)
 	}
-	if age < 24*time.Hour {
-		return fmt.Sprintf("-%dh", int(age.Hours()))
+	return true
+}
+
+func formatTimelineLabel(ts time.Time, sameDay bool) string {
+	if sameDay {
+		return ts.Format("15:04")
 	}
-	return fmt.Sprintf("-%dd", int(age.Hours()/24))
+	return ts.Format("01-02 15:04")
 }
 
 // gpuRings holds per-GPU ring buffers.
@@ -792,22 +799,13 @@ func sampleTimeLabels(samples []platform.LiveMetricSample) []string {
 	if len(samples) == 0 {
 		return labels
 	}
-	sameDay := true
-	first := samples[0].Timestamp.Local()
-	for _, s := range samples {
-		ts := s.Timestamp.Local()
-		if ts.Year() != first.Year() || ts.YearDay() != first.YearDay() {
-			sameDay = false
-			break
-		}
-	}
+	times := make([]time.Time, len(samples))
 	for i, s := range samples {
-		ts := s.Timestamp.Local()
-		if sameDay {
-			labels[i] = ts.Format("15:04")
-		} else {
-			labels[i] = ts.Format("01-02 15:04")
-		}
+		times[i] = s.Timestamp
+	}
+	sameDay := timestampsSameLocalDay(times)
+	for i, s := range samples {
+		labels[i] = formatTimelineLabel(s.Timestamp.Local(), sameDay)
 	}
 	return labels
 }