devshell: Accept flake config in build-n-switch

Pass `--accept-flake-config` explicitly because `doas` drops the
devshell configuration that enables it. This avoids prompts for the
flake’s binary cache settings when rebuilding as root.

AGENTS.md

@@ -35,7 +35,7 @@ see its help, or browse `devshell/commands.nix` / `devshell/install.nix` / `devs
 Common ones:
 - `fmt` — format Nix with `nixpkgs-fmt` (the canonical formatter here).
 - `build-system <host> [nix args]` — build a NixOS system's `toplevel`.
-- `build-n-switch <args>` — wraps `doas nixos-rebuild --flake .`.
+- `build-n-switch <args>` — wraps `doas nixos-rebuild --accept-flake-config --flake .`.
 - `build-home <name>` / `home-switch` — build / switch a home-manager config.
 - `run-vm <host>` — build & boot a system as a dev VM (installs `.keys/dev.key` into the VM).
 - `build-iso` / `build-kexec` / `build-netboot <host>` — alternate build outputs via `config.my.buildAs.*`.

devshell/commands.nix

@@ -106,7 +106,8 @@ in
         # HACK: Upstream changes in Git + Nix makes this necessary
         # https://github.com/NixOS/nix/issues/10202
         doas git config --global --add safe.directory "$PWD"
-        doas nixos-rebuild --flake . "$@"
+        # doas drops the devshell's NIX_USER_CONF_FILES, including accept-flake-config.
+        doas nixos-rebuild --accept-flake-config --flake . "$@"
       '';
     }
     {

docs/deployment.md

@@ -82,7 +82,7 @@ command with no arguments for its help. From
 |---|---|
 | `check-system <host> [nix args]` | Evaluates `.#nixosConfigurations."<host>".config.system.build.toplevel.drvPath` — catches module/option errors without building. Prefer this to validate a config change. |
 | `build-system <host> [nix args]` | Builds the system's `toplevel` (extra args pass through to `nix build`). |
-| `build-n-switch <args>` | `doas nixos-rebuild --flake .` (adds the repo as a git `safe.directory` for root first). |
+| `build-n-switch <args>` | `doas nixos-rebuild --accept-flake-config --flake .` (accepts the flake's cache settings and adds the repo as a git `safe.directory` for root first). |
 | `build-home <name> [nix args]` | Builds `.#homeConfigurations."<name>".activationPackage`. |
 | `home-switch [args]` | `home-manager switch --flake .`. |
 | `deploy [args]` | `deploy-rs --skip-checks` (wrapper package in `devshell/default.nix`). |