Layers

The layers are crates. Cargo enforces the DAG through the pkgs/mrlyrs/* manifests: core ← math ← ui and core ← font ← ui; core ← music ← apps; os leans only on core; apps sees all of those; net sees everything and owns the card. pkgs/mrlyssg is the static-site parts: core ← ssg and font ← ssg, nothing else. Nothing in pkgs/ imports net, ssg least of all; the apps/* binaries (cli, gui, git) sit on top and may.

The one lint

utils/layers.py enforces the single rule Cargo cannot: apps never import other apps. Shared app code goes in a kit, not a sibling. Run it before shipping (ship.py does).

Inside a crate

Module boundaries inside a merged crate (math/physics/crypto in mrlymath) are convention, not compiler-checked. Families keep talking through their mod.rs face.