Question juridique clé
Whether cantonal procedural law could grant standing to challenge the mutual assistance order.
Solution extraite
Standing in mutual assistance proceedings is governed exclusively by federal law; cantonal procedural rules cannot enlarge it.
Motifs extraits
The field is exhaustively regulated by the EIMP, notably Art. 21(3) and Art. 80h EIMP, so cantonal rules on party standing do not apply.