[clhodapp]

Adds the last three survey integrations, caisson.topology (over nix-topology), caisson.kubenix and caisson.nixidy. It also has the cost fix that makes room for them. This PR is based on #100. Merge #94 through #100 first, then change the base of this PR to main.

The cost fix

perf(core) declares the export settings of every class, caisson.modules.<class>.export.enabled and .exported, in a single option, caisson.modules. It is an attribute set by class of plain values (lazyAttrsOf (lazyAttrsOf raw)). Before, there were two options for every registered class in every evaluation. Now a class no module sets costs nothing to evaluate.

• Definitions are written the same way as before. Priorities on exported still take effect.
• Two definitions of exported for one class now conflict instead of merging. No module in caisson or in the workspace defines it twice.
• A class with no registered module, or a key other than export and exported, is refused when the exports are read.
• I tried submodules first, but each submodule is an evaluation of its own, and the gate on module-system evaluations refused them.

The fix took caisson's overhead in the eval-weight check from 4.07 MB to 3.66 MB. With the three integrations added it is 3.83 MB. The ceiling is still 4.28 MB.

Each integration still costs about 60 KB through caisson-core's composition. caisson-core merges every overlay's result into the library with acc.prev // result, so each overlay copies the accumulated library once in every composed library. Removing that cost would mean changing caisson-core, and this PR doesn't.

The integrations

• topology:
  • A topology configuration is the diagram of the NixOS configurations declared inside it. Those machines get nix-topology's NixOS module by default.
  • caisson evaluates nix-topology's topology modules on the composed library, on the selected package set extended with nix-topology's packages, with nixosConfigurations set to the machines at its system.
  • The configuration named default is published as topology.<system>, where nix-topology's flake module publishes it.
  • The test declares two machines inside a topology configuration. The nodes, and the derivation of the rendered diagram, match nix-topology's own evaluation over the same machines evaluated with its NixOS module.
• kubenix:
  • caisson makes the evaluation kubenix's evalModules makes, on the composed library extended with upstreamables.nix, with the same kubenix argument.
  • The configuration is published as kubenixConfigurations.<system>.<name>, its evaluation. Its config.kubernetes.result is the JSON that kubectl apply -f reads.
  • The test checks that it is the derivation kubenix's evalModules gives the same module.
• nixidy:
  • caisson calls nixidy's own mkEnv with the composed library as lib, and adds the composed library's namespaces through mkEnv's libOverlay.
  • The configuration is published as nixidyEnvs.<system>.<name>, which the nixidy CLI reads.
  • mkEnv returns no options, so, as with terranix, a nixidy configuration holds no configurations beneath it.
  • The test checks that the environmentPackage derivation is the one mkEnv renders from the same module.

Checks

• nix flake check passes.
• All 18 workspace consumers pass nix flake check --no-build with this branch in place of both caisson pins. Consumers that set caisson.modules.<class>.exported, such as ch-ai-workbench and ch-emacs-config, are among them.

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