Add queue high water marks to handler statistics

- Track the maximum queue length seen for each handler
- Display high water marks on the status page with percentage
- Helps identify which handlers are experiencing queue pressure

internal/server/handlers.go

@@ -177,6 +177,7 @@ func (s *Server) handleStats() http.HandlerFunc {
 		Name               string  `json:"name"`
 		QueueLength        int     `json:"queue_length"`
 		QueueCapacity      int     `json:"queue_capacity"`
+		QueueHighWaterMark int     `json:"queue_high_water_mark"`
 		ProcessedCount     uint64  `json:"processed_count"`
 		DroppedCount       uint64  `json:"dropped_count"`
 		AvgProcessTimeMs   float64 `json:"avg_process_time_ms"`
@@ -284,6 +285,7 @@ func (s *Server) handleStats() http.HandlerFunc {
 				Name:               hs.Name,
 				QueueLength:        hs.QueueLength,
 				QueueCapacity:      hs.QueueCapacity,
+				QueueHighWaterMark: hs.QueueHighWaterMark,
 				ProcessedCount:     hs.ProcessedCount,
 				DroppedCount:       hs.DroppedCount,
 				AvgProcessTimeMs:   float64(hs.AvgProcessTime.Microseconds()) / microsecondsPerMillisecond,

internal/streamer/streamer.go

@@ -59,6 +59,7 @@ type handlerMetrics struct {
 	totalTime          time.Duration // Total processing time (for average calculation)
 	minTime            time.Duration // Minimum processing time
 	maxTime            time.Duration // Maximum processing time
+	queueHighWaterMark int           // Maximum queue length seen
 	mu                 sync.Mutex    // Protects the metrics
 }
 
@@ -217,6 +218,7 @@ type HandlerStats struct {
 	Name               string
 	QueueLength        int
 	QueueCapacity      int
+	QueueHighWaterMark int
 	ProcessedCount     uint64
 	DroppedCount       uint64
 	AvgProcessTime     time.Duration
@@ -238,6 +240,7 @@ func (s *Streamer) GetHandlerStats() []HandlerStats {
 			Name:               fmt.Sprintf("%T", info.handler),
 			QueueLength:        len(info.queue),
 			QueueCapacity:      cap(info.queue),
+			QueueHighWaterMark: info.metrics.queueHighWaterMark,
 			ProcessedCount:     info.metrics.processedCount,
 			DroppedCount:       info.metrics.droppedCount,
 			MinProcessTime:     info.metrics.minTime,
@@ -550,6 +553,13 @@ func (s *Streamer) stream(ctx context.Context) error {
 			select {
 			case info.queue <- &msg:
 				// Message queued successfully
+				// Update high water mark if needed
+				queueLen := len(info.queue)
+				info.metrics.mu.Lock()
+				if queueLen > info.metrics.queueHighWaterMark {
+					info.metrics.queueHighWaterMark = queueLen
+				}
+				info.metrics.mu.Unlock()
 			default:
 				// Queue is full, drop the message
 				atomic.AddUint64(&info.metrics.droppedCount, 1)

internal/templates/status.html

@@ -264,6 +264,10 @@
                         <span class="metric-label">Queue</span>
                         <span class="metric-value">${handler.queue_length}/${handler.queue_capacity}</span>
                     </div>
+                    <div class="metric">
+                        <span class="metric-label">High Water Mark</span>
+                        <span class="metric-value">${handler.queue_high_water_mark}/${handler.queue_capacity} (${Math.round(handler.queue_high_water_mark * 100 / handler.queue_capacity)}%)</span>
+                    </div>
                     <div class="metric">
                         <span class="metric-label">Processed</span>
                         <span class="metric-value">${formatNumber(handler.processed_count)}</span>