Use this small template to reproduce bugs in den.
Create a minimal bug reproduction at modules/bug.nix
See also Den debugging tips
Then run tests:
nix flake checkPlease share a link to your reproduction repo, showing the CI step and the error at CI build.
If you are contributing a bug-fix PR, you can use the following command to use your local den checkout.
cd <den-working-copy>
nix flake check --override-input den . ./templates/bogus