fix: update buffer_cache_size metric with actual history cache size

The buffer_cache_size metric was defined but never updated, always showing 0.

Fix:
- Add historyCacheSize parameter to recordBufferFlush function
- Pass historyCache.size from event-buffer.ts when recording flush metrics
- Update both bufferCacheSize and bufferHistoryCacheSize metrics

src/Utils/event-buffer.ts

@@ -410,9 +410,9 @@ export const makeEventBuffer = (
 		}
 	}
 
-	const recordFlushMetrics = (eventCount: number, forced: boolean) => {
+	const recordFlushMetrics = (eventCount: number, forced: boolean, cacheSize: number) => {
 		if (metricsModule) {
-			metricsModule.recordBufferFlush(eventCount, forced)
+			metricsModule.recordBufferFlush(eventCount, forced, cacheSize)
 		}
 	}
 
@@ -553,7 +553,7 @@ export const makeEventBuffer = (
 		stats.historyCacheSize = historyCache.size
 
 		// Record metrics
-		recordFlushMetrics(eventCount, force)
+		recordFlushMetrics(eventCount, force, historyCache.size)
 
 		// Log with [BAILEYS] prefix - use getMode() to avoid duplicating mode calculation logic
 		const flushDuration = Date.now() - flushStartTime

src/Utils/prometheus-metrics.ts

@@ -1855,15 +1855,23 @@ export function recordEventBuffered(eventType: string, count: number = 1): void
  * Record a buffer flush operation
  * Used by event-buffer.ts for metrics integration
  */
-export function recordBufferFlush(eventCount: number, forced: boolean): void {
+export function recordBufferFlush(eventCount: number, forced: boolean, historyCacheSize?: number): void {
 	try {
 		// Use the main metrics object which has the correct labels ['type', 'reason']
 		metrics.bufferFlushes?.inc({ type: 'event', reason: forced ? 'forced' : 'normal' })
 
+		// Update buffer cache size if provided
+		if (typeof historyCacheSize === 'number') {
+			metrics.bufferCacheSize?.set({}, historyCacheSize)
+		}
+
 		// Also update the lazy-loaded event buffer metrics for detailed tracking
 		const ebMetrics = getEventBufferMetrics()
 		ebMetrics.bufferFlushEvents?.observe({}, eventCount)
 		ebMetrics.bufferCurrentSize?.set({}, 0) // Reset after flush
+		if (typeof historyCacheSize === 'number') {
+			ebMetrics.bufferHistoryCacheSize?.set({}, historyCacheSize)
+		}
 	} catch {
 		// Metrics not initialized, ignore silently
 	}