Only one of the things that makes what you're describing unworkable is that "concerned parties" include arbitrary members of the public. Anyone who can't afford to spend a year sequestered in a room can't so much as write a letter to their representative?

Another is that they would just agree on what to do before the official start of the process. Or learn to speak in code. Or pass notes to each other off camera etc.

The closest approximation that might actually do something would be to require the final version of any piece of legislation to be published a year before the final vote. Then the product of a backroom deal can't be enacted before anyone else has a chance to mount an opposition.

Another would be to make it easier to repeal things than to pass them. A lot of current corruption relies on the misfeature that we apply the same purposely-arduous process intended to inhibit bad things from passing as the requirement to un-pass existing bad things, so then if they can corrupt the entire process once they only have to maintain control of a single branch to prevent it from being rolled back.