[clhodapp]

A default that a level adds through forChildren reaches every configuration of its class beneath the level, at any depth. Most of what a level gives says what the configurations directly beneath it live on: the deployment options of a colmena node, the file systems of a disk layout, the hardware of a facter report. That stops being true one machine further down. A NixOS configuration declared inside one of those machines inherited them all.

A configuration's evaluation may now return forNearestChildren.extraDefaultModuleImports, by class. These additions connect at the nearest configurations of their class beneath the level and go no deeper:

• Each manifest carries nearestPending: by class, a list of { select; file; level; nearest = true; }, the additions on their way down.
• Beneath a parent, nearestPending is what reached the parent, minus the parent's own class, followed by the parent's own additions. Systems and configurations with no class pass it on unchanged.
• At a configuration of class C, defaultModuleImports.C is what it inherits, followed by nearestPending.C.
• inheritedFrom drops entries marked nearest before passing defaults down, so they stop at the configuration they reached.

mkConfiguration takes class ? null for this. caisson passes the class of each configuration, so caisson must take this change before it passes class.

Tests: the new test lifecycleNearestAdditionsConnectOnce checks that an addition reaches the nearest configuration of its class through a configuration of another class, and that a configuration of that class nested inside it does not inherit it. Locally, nix flake check and the test summary (133 passed) pass.

The caisson side, the option caisson.forNearestChildren and the defaults moved to it, follows in nix-caisson/caisson.

🤖 Generated with Claude Code