I don't agree, but maybe I don't understand the question.
It's indeed "in Congress".
The National Assembly and the Senate gather together AND become a temporary own institution which is called "Congrès".
This "Congrès" (with a capital letter in the French Constitution) has its own "bureau" (which is the same as the "bureau" of the National Assembly). It's also the case for the President (who is the president of the National Assembly).
And the majorities usually required in front of the "Congrès" (see constitutional amendments, article 89) are global ones: you don't count Assemblymen on one hand and Senators on the other hand.
Right, the
Congrès is the joint session of Parliament. During the
Congrès, the National Assembly and the Senate convene in one place; in other words, they are united in congress (with a lowercase C). "Congress" with a capital C, as used in the United States, means the national legislature itself, not the joint session. So the Congress would translate into the French system as the Parliament. Any formal body can meet in congress, but the term "Congress" refers specifically to the national legislature
The
Congrès, as you say, has a temporary existence, like the joint sessions of Congress in the United States. The Congress and Parliament, however, are permanent institutions. There is only one Congress in the United States, and only one Parliament in France, but any formal body can meet in congress (this is what was meant by the Socialist Party's
Congrès in Reims last year, which was simply the equivalent of a party convention).
