Duplicated values and the purpose of the router system

[ProducerMatt]

Hi there, I've been trying to migrate my NixOS config to den as it seems like it will ultimately make more sense and be easier to use. To avoid creating a bunch of bugs at once, I'm trying to migrate my repo with as few changes as possible, after which I can start refactoring it to make the most sense in den.

I've gotten stuck on a duplicate values bug that I can't seem to duplicate in the test repo, the classic "aspect being invoked multiple times" bug. Here is a commit of my repo at a state with the issue, running nix flake check will induce it. I was able to fix a few occurrences by limiting the aspect containing it to {OS,host}, however my progress was halted once I got to a behavior I wanted to put in aspects.default. I tried using take.exactly but this didn't fix the problem.

A core issue is I don't understand the dependency/routing system or why it needs to be able to output multiple times.

1. I missed the dependency page because I thought it was a section name, until the README linked me there and I realized I could have clicked it. (Since none of the other section headers have text, it might make sense to make it the first page of the section rather than living on the top level.)
2. I don't know any way to figure out why an aspect is being induced twice. A debug option showing what the dependency system is wanting would be extremely valuable.
3. I don't understand why any non-parametric aspect should ever be induced twice on the same system -- won't it only ever cause a duplication error? Or is this actually unintended behavior, and I've encountered a duplication bug?

Thanks for your work, would love to see any advancement in NixOS management as it's ornery at its best.

[vic]

Hey, I have not been able to find time to investigate this, nor look carefully at your repo, if you have made some progress please keep us updated.

[ProducerMatt]

I haven't made any progress yet. 😬