Great mod! Exactly what I needed when getting frustrated that wagons' construction bots were picking up trash even though their wagon was full. I also was doing my best to try and use a single train with multiple wagons, each with construction bots, but sometimes construction bots would die and then I couldn't figure out a way to automatically re-fill each wagon with exactly 100 construction bots, since you can't count the items in a single wagon - only the entire train, so my 5-car train would end up with lots of construction robots in one wagon but not enough in another. Your mod solved all that, thank you!
The only thing I noticed is that, say I have two Construction Wagons, one that holds tracks and another that holds landfill. If I add both tracks and landfill to the first wagon (i.e. if I want to use a single requester chest for all requests), it doesn't seem to push the landfill to the second wagon, even though it has the filter slots for it. I had to add a third "normal" wagon, and then the first wagon would send the landfill to the normal wagon, and then the second wagon would take the landfill from it to fill its filter slots.
That was working fine, even with the extra step, but then I thought, hey, I've got that extra wagon now, that's great, it will fill up with wood and stone from trees and rocks and junk, so I'll put some inserters next to automatically empty it at my station when my train returns and is ready for refilling. But now the problem was that when the first wagon sent the landfill to the third wagon, and my inserters immediately grabbed them out before the second wagon took them! I tried setting the third wagon's inserters to have a blacklist equal to the requested items signal, but that didn't work because as soon as the last landfill is put into the train, there's not a request for it anymore, so there's not a blacklist for it anymore, so the third wagon's inserters grab it and the cycle repeats.
What I ended up doing is some arithmetic combinator voodoo to make the requested items signal "linger" for a while on the last inserters blacklist wire, even after the request signals were gone from the source wire. They linger long enough to give the second wagon enough time to grab what it wants.
If you ever have spare time you might want to make construction wagons send their trash to other construction wagons that want the items first, before sending the trash to the normal wagons. That way other people won't need to do combinator voodoo too :)
