dev: NixOS 25.11 매뉴얼 로컬 사본 추가

nixpkgs nixos-25.11 브랜치의 nixos/doc/manual/ 디렉토리를 sparse clone으로
가져와 ~/obsidian/dev/nixos-manual/에 복사. _index.md에 구조/갱신 방법 정리.

오프라인 참조 + AI 에이전트 컨텍스트용. sandbox-tokyo 같은 NixOS 노드 운영 시
빠른 참조로 사용.

dev/nixos-manual/development/bootspec.chapter.md

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+# Bootspec {#sec-bootspec}
+
+Bootspec is a feature introduced in [RFC-0125](https://github.com/NixOS/rfcs/pull/125) in order to standardize bootloader support and advanced boot workflows such as SecureBoot and potentially more.
+The reference implementation can be found [here](https://github.com/NixOS/nixpkgs/pull/172237).
+
+The creation of bootspec documents is enabled by default.
+
+## Schema {#sec-bootspec-schema}
+
+The bootspec schema is versioned and validated against [a CUE schema file](https://cuelang.org/) which should considered as the source of truth for your applications.
+
+You will find the current version [here](../../../modules/system/activation/bootspec.cue).
+
+## Extensions mechanism {#sec-bootspec-extensions}
+
+Bootspec cannot account for all usecases.
+
+For this purpose, Bootspec offers a generic extension facility [`boot.bootspec.extensions`](options.html#opt-boot.bootspec.extensions) which can be used to inject any data needed for your usecases.
+
+An example for SecureBoot is to get the Nix store path to `/etc/os-release` in order to bake it into a unified kernel image:
+
+```nix
+{ config, lib, ... }:
+{
+  boot.bootspec.extensions = {
+    "org.secureboot.osRelease" = config.environment.etc."os-release".source;
+  };
+}
+```
+
+To reduce incompatibility and prevent names from clashing between applications, it is **highly recommended** to use a unique namespace for your extensions.
+
+## External bootloaders {#sec-bootspec-external-bootloaders}
+
+It is possible to enable your own bootloader through [`boot.loader.external.installHook`](options.html#opt-boot.loader.external.installHook) which can wrap an existing bootloader.
+
+Currently, there is no good story to compose existing bootloaders to enrich their features, e.g. SecureBoot, etc.
+It will be necessary to reimplement or reuse existing parts.