Question juridique clé
Whether the refusal of joinder was a final decision requiring exhaustion of ordinary cantonal remedies
Solution extraite
The refusal of joinder was an incidental decision; ordinary and nullity appeals in canton law were unavailable, so the federal public-law appeal was admissible.
Motifs extraits
The decision did not end the main proceedings and caused no irreparable legal harm; nevertheless, joinder-refusal decisions may be challenged immediately because waiting until final judgment would undermine procedural economy.