[clhodapp]

Builds on nix-caisson/caisson-core#52, merged. This branch pins caisson-core to main, which has it.

The manifest of each configuration now carries moduleImports, the account of its module selection that design section 5 asks for. It answers "why is this module here":

• act: default when the configuration took the default of its class, appended when it gave extraModuleImports alone, and reset when it gave moduleImports;
• position: the file and line number where it gave that argument;
• default: the default in force, each entry with its registry key, the level that added it and the file that defines it;
• selected: the registry keys of the modules it selected.

For the pinned-world machine, the account reads:

• The top passes moduleImports = _modules: [ ], so its record is act = "reset", with tests/pinned-world/default.nix and the line number.
• The NixOS configuration records act = "default", with modules.nixos.caisson/default from the class default.
• The home-manager configuration inside it records the class default, then modules.homeManager.nixos-parent, added at [ { system x86_64-linux } { nixos probe } ] from modules/nixos/default/caisson.

How. mkModuleConfiguration takes selection = { class; args; }, and every integration passes its class and its arguments. The new selectionAccountOf works out the account, and the builder records it through caisson-core's recordFromEvaluation. Each forChildren.extraDefaultModuleImports addition now reaches caisson-core as { select; file; }, with the file that defines it, and caisson-core adds the level. moduleImportsOf reads select from each entry. inSource, registryPartsOf and the new registryKeyOf moved out of declarationEventsOf so both can use them.

Test. The pinned-world test selectionsRecordHowModulesWereChosen checks the three accounts above. nix flake check passes locally, including the VM tests and the evaluation-cost gate. No workspace consumer reads a manifest's defaultModuleImports, the field whose shape changed.

The docs are in nix-caisson/nix-caisson.github.io#82.

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