what weight to use when weighing pasta for dieting purposes? I presume that, ceteris paribus, the same amount of pasta cooked is significantly heavier than the same amount uncooked.

So what is the standard?
There is no standard. (Btw. this also applies to rice)

Any source (calorie table, diet plan, recipe..) should specify what they are talking about when giving values.

That said, for recipes, the context should clarify. If it includes a full cooking step, assume dried. If it calls for precooked, is usually mentioned.