snapshot: prune speedtests older than 30 days (retention via existing storage primitive)

cmd/snapshot/main.go

@@ -43,7 +43,16 @@ type snapshot struct {
 // buildSpeedtestSnapshot collects the last 200 speedtest rows + per-node
 // medians over 24h/7d/30d windows. Aggregate errors are logged but
 // non-fatal — the rest of the snapshot still ships.
+//
+// Side effect: prunes speedtests older than 30 days. Retention is colocated
+// with snapshot rebuild because both run on the same timer cadence and the
+// storage layer already has the DeleteSpeedTestsBefore primitive.
 func buildSpeedtestSnapshot(ctx context.Context, st *storage.Store) (*SpeedtestSnapshot, error) {
+	if deleted, err := st.DeleteSpeedTestsBefore(ctx, time.Now().Add(-30*24*time.Hour).Unix()); err != nil {
+		log.Printf("speedtests retention (non-fatal): %v", err)
+	} else if deleted > 0 {
+		log.Printf("speedtests retention: pruned %d rows older than 30 days", deleted)
+	}
 	recent, err := st.ListRecentSpeedTests(ctx, 200)
 	if err != nil {
 		return nil, err