The solution for this would have been a diplo popup window: "Salzburg is plotting to attack Austria. Here are the allies who would be called. They are asking you if you would back their declaration of war. If so, they can declare war within 30 days." Player options: "Yes, I will prepare my forces! / No, the time is not right."
That way, they can go ahead and do the DoW if they want, but know that they cannot call you as an offensive ally.
But the other advantage of this is that you can prepare by setting your sliders and starting to move your troops around, rather than get caught flat-footed with all your morale at zero and your trade fleets exposed.
That way, they can go ahead and do the DoW if they want, but know that they cannot call you as an offensive ally.
But the other advantage of this is that you can prepare by setting your sliders and starting to move your troops around, rather than get caught flat-footed with all your morale at zero and your trade fleets exposed.