Improve position validation logging and reduce spam

- Remove duplicate validation logging between mergeAircraftData and updateHistories
- Add rate limiting: errors logged max once per 10 seconds per aircraft
- Add rate limiting: warnings logged max once per 30 seconds per aircraft
- Only log first error/warning message to reduce log verbosity
- Clean up validation log entries when aircraft become stale
- Maintain memory efficiency with automatic cleanup

This significantly reduces log spam from aircraft with persistent
position validation issues (e.g., CPR decoding problems).

🤖 Generated with [Claude Code](https://claude.ai/code)

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

internal/merger/merger.go

@@ -271,6 +271,7 @@ type Merger struct {
 	historyLimit  int                       // Maximum history points to retain
 	staleTimeout  time.Duration             // Time before aircraft considered stale (15 seconds)
 	updateMetrics map[uint32]*updateMetric  // ICAO24 -> update rate calculation data
+	validationLog map[uint32]time.Time      // ICAO24 -> last validation log time (rate limiting)
 }
 
 // updateMetric tracks recent update times for calculating update rates.
@@ -301,6 +302,7 @@ func NewMerger() (*Merger, error) {
 		historyLimit:  500,
 		staleTimeout:  15 * time.Second, // Aircraft timeout - reasonable for ADS-B tracking
 		updateMetrics: make(map[uint32]*updateMetric),
+		validationLog: make(map[uint32]time.Time),
 	}, nil
 }
 
@@ -453,10 +455,14 @@ func (m *Merger) mergeAircraftData(state *AircraftState, new *modes.Aircraft, so
 		validation := m.validatePosition(new, state, timestamp)
 
 		if !validation.Valid {
-			// Log validation errors and skip position update
+			// Rate-limited logging: only log once every 10 seconds per aircraft
+			if lastLog, exists := m.validationLog[new.ICAO24]; !exists || timestamp.Sub(lastLog) > 10*time.Second {
 				icaoHex := fmt.Sprintf("%06X", new.ICAO24)
-			for _, err := range validation.Errors {
-				log.Printf("[POSITION_VALIDATION] ICAO %s: REJECTED position update - %s", icaoHex, err)
+				// Only log first error to reduce spam
+				if len(validation.Errors) > 0 {
+					log.Printf("[POSITION_VALIDATION] ICAO %s: REJECTED - %s", icaoHex, validation.Errors[0])
+					m.validationLog[new.ICAO24] = timestamp
+				}
 			}
 		} else {
 			// Position is valid, proceed with normal logic
@@ -483,10 +489,15 @@ func (m *Merger) mergeAircraftData(state *AircraftState, new *modes.Aircraft, so
 			}
 		}
 
-		// Log warnings even if position is valid
-		for _, warning := range validation.Warnings {
+		// Rate-limited warning logging
+		if len(validation.Warnings) > 0 {
+			// Only log warnings once every 30 seconds per aircraft
+			warningKey := new.ICAO24 + 0x10000000 // Offset to differentiate from error logging
+			if lastLog, exists := m.validationLog[warningKey]; !exists || timestamp.Sub(lastLog) > 30*time.Second {
 				icaoHex := fmt.Sprintf("%06X", new.ICAO24)
-			log.Printf("[POSITION_VALIDATION] ICAO %s: WARNING - %s", icaoHex, warning)
+				log.Printf("[POSITION_VALIDATION] ICAO %s: WARNING - %s", icaoHex, validation.Warnings[0])
+				m.validationLog[warningKey] = timestamp
+			}
 		}
 	}
 
@@ -611,19 +622,8 @@ func (m *Merger) updateHistories(state *AircraftState, aircraft *modes.Aircraft,
 				Longitude: aircraft.Longitude,
 				Source:    sourceID,
 			})
-		} else {
-			// Log validation errors for debugging
-			icaoHex := fmt.Sprintf("%06X", aircraft.ICAO24)
-			for _, err := range validation.Errors {
-				log.Printf("[POSITION_VALIDATION] ICAO %s: REJECTED - %s", icaoHex, err)
-			}
-		}
-
-		// Log warnings even for valid positions
-		for _, warning := range validation.Warnings {
-			icaoHex := fmt.Sprintf("%06X", aircraft.ICAO24)
-			log.Printf("[POSITION_VALIDATION] ICAO %s: WARNING - %s", icaoHex, warning)
 		}
+		// Note: Validation errors/warnings are already logged in mergeAircraftData
 	}
 
 	// Signal history
@@ -847,6 +847,9 @@ func (m *Merger) CleanupStale() {
 		if now.Sub(state.LastUpdate) > m.staleTimeout {
 			delete(m.aircraft, icao)
 			delete(m.updateMetrics, icao)
+			// Clean up validation log entries
+			delete(m.validationLog, icao)
+			delete(m.validationLog, icao+0x10000000) // Warning key
 		}
 	}
 }