fix(gateway): prefer known JT808 identity snapshot

go/vehicle-gateway/internal/identity/resolver.go

@@ -612,6 +612,13 @@ func (r *MySQLResolver) enrichResolvedJT808SourceMetadata(ctx context.Context, e
 func (r *MySQLResolver) lookupJT808Registration(ctx context.Context, phone string) (vin string, deviceID string, plate string, cacheStatus string, err error) {
 	phone = normalizePhone(phone)
 	now := time.Now()
+	// The immutable snapshot is the authoritative vehicle binding. Registration
+	// and authentication frames can create a short-lived local session whose VIN
+	// is still "unknown"; letting that session win would permanently mask a known
+	// snapshot because every location frame refreshes the session TTL.
+	if snapshot, ok := r.snapshotRegistration(phone); ok && snapshot.canResolveVehicle() {
+		return snapshot.vin, snapshot.deviceID, snapshot.plate, "snapshot", nil
+	}
 	var stale registrationCacheEntry
 	hasStale := false
 	r.lookupMu.Lock()
@@ -659,6 +666,11 @@ func (r *MySQLResolver) lookupJT808Registration(ctx context.Context, phone strin
 	return entry.vin, entry.deviceID, entry.plate, "", nil
 }
 
+func (e registrationCacheEntry) canResolveVehicle() bool {
+	vin := strings.TrimSpace(e.vin)
+	return (vin != "" && !strings.EqualFold(vin, "unknown")) || strings.TrimSpace(e.plate) != ""
+}
+
 func addIdentityMetadata(parsed map[string]any, source string, value string) {
 	if parsed == nil {
 		return