docs: narrow NixOS maintainer validation defaults

modules/capabilities/skills/nixos-maintainer/SKILL.md

@@ -15,15 +15,10 @@ secret, credential, and application-owned state outside the Nix store. Verify
 unfamiliar pinned interfaces against the exact package source or current primary
 documentation.
 
-Preserve unrelated work in a dirty tree. Make the smallest complete change,
+Preserve unrelated work. Format touched Nix files and use the narrowest useful
-format touched Nix files with the repository formatter, and validate only the
+evaluation for configuration changes. Build affected hosts only when needed to
-affected hosts. Ordinarily run:
+resolve a concrete concern or explicitly requested; instruction-only edits do
+not need system builds. Do not add tests or migration/compatibility code by
+default. Explain manual steps for breaking changes.
 
-```sh
+Do not switch or boot a generation unless the user explicitly requests activation.
-nix flake check --no-build --quiet
-nix build --no-link --quiet .#nixosConfigurations.<host>.config.system.build.toplevel
-```
-
-Start with a narrower evaluation when it can fail faster. Inspect targeted
-failure logs only. Do not switch or boot a generation unless the user explicitly
-requests activation.