perf: add visitReverse to logger ring buffer, avoid full copy in RecentLogs

RecentLogs previously copied ALL ring buffer entries via recent(0),
then iterated in reverse to filter. Now uses visitReverse() which
iterates newest-to-oldest under read lock, copying only matching
entries — eliminates the full-buffer allocation for filtered queries.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/logger/logger.go

@@ -93,6 +93,20 @@ func (rb *logRingBuffer) recent(limit int) []LogEntry {
 	return result
 }
 
+// visitReverse iterates entries from newest to oldest under the read lock.
+// The callback receives a pointer to the internal entry (valid only during
+// the call). Return false to stop iteration.
+func (rb *logRingBuffer) visitReverse(fn func(*LogEntry) bool) {
+	rb.mu.RLock()
+	defer rb.mu.RUnlock()
+	for i := 0; i < rb.count; i++ {
+		idx := (rb.head - 1 - i + len(rb.entries)) % len(rb.entries)
+		if !fn(&rb.entries[idx]) {
+			return
+		}
+	}
+}
+
 // LogSubscriber receives log entries matching its filter.
 type LogSubscriber struct {
 	Ch     chan LogEntry
@@ -355,20 +369,23 @@ func broadcastToSubscribers(entry LogEntry) {
 // RecentLogs returns recent log entries from the ring buffer, optionally filtered
 // by minimum level and component. The Caller field is stripped for security.
 func RecentLogs(minLevel LogLevel, component string, limit int) []LogEntry {
-	all := ringBuf.recent(0) // get all
 	result := make([]LogEntry, 0, limit)
-	for i := len(all) - 1; i >= 0 && len(result) < limit; i-- {
-		e := all[i]
+	ringBuf.visitReverse(func(e *LogEntry) bool {
+		if len(result) >= limit {
+			return false
+		}
 		if lvl, ok := levelFromName[e.Level]; ok && lvl < minLevel {
-			continue
+			return true
 		}
 		if component != "" && e.Component != component {
-			continue
-		}
-		e.Caller = ""                      // strip for security
-		e.Fields = SanitizeFields(e.Fields) // mask sensitive values
-		result = append(result, e)
+			return true
 		}
+		entry := *e
+		entry.Caller = ""
+		entry.Fields = SanitizeFields(e.Fields)
+		result = append(result, entry)
+		return true
+	})
 	// Reverse so oldest first
 	for i, j := 0, len(result)-1; i < j; i, j = i+1, j-1 {
 		result[i], result[j] = result[j], result[i]