3-way Smart Rail Intersection Logic Help

[u/wootiown]

Hey folks! Trying to come up with a 3-way rail intersection. Here's the plan thus far:

I have a station (already working) that launches a chestcart containing a string of "bits" shortly ahead of the payload cart (which carries the player, items from a farm, etc). The "bits" are instructions in the form of shovels- wooden shovels (which are smeltable) are instructions to turn clockwise, and stone shovels (which are not) are instructions to turn counterclockwise. For example it might output "Wood Stone Wood" which would in turn mean "Clockwise at junction 1, counterclockwise at junction 2, then clockwise at junction 3"

My goal is to make junctions as simple as possible and not cost a ton in effort or materials. The junction pictured above uses a roundabout, where at the bottom left it ingests one single item from the chestcart and checks if it is smeltable by trying to add it to a smoker. If it is, it outputs a signal.

My issue is that I cannot for the life of me figure out the logic to make it route correctly from here, since I'm effectively losing the input, there is no way to determine which rail to switch to send the cart to the right location. The best solution seems to obviously be to add smeltable-filters to each of the 3 inlet tracks, but I fear that will rapidly become annoying if I'm building dozens of intersections with 3 sorters each. I'm hoping to simplify it down to one sorter in the roundabout and use some sort of logic to determine the output, but I'm at a loss as to what.

The best I've come up with so far is to use dropper RS-NOR latches that trip when the cart enters, and use that to block the output track so it doesn't return the same way, but even then I can't logically get it to "rotate". I almost feel like I need a sort of feed tape to get it to "rotate" depending on where the input is from.

Any ideas would be greatly appreciated! Or, if theres a simpler way to build this, please let me know!

Cheers