testing

modules/wsl/builder.nix

@@ -0,0 +1,54 @@
+# WSL NixOS — advertise this host as a remote Nix builder.
+#
+# Why a dedicated module instead of inlining into configurations/wsl.nix:
+# every "what makes this WSL different from a desktop/server" concern
+# belongs under modules/wsl/ — that is the contract the device-type import in
+# modules/default.nix wires up. Keeping it here means flipping the feature on
+# later on another WSL host (e.g. a future vetymae-2) is one import away.
+#
+# The `host.builder.enable` option itself is declared in
+# modules/options.nix (cross-module).
+{
+  config,
+  lib,
+  ...
+}:
+{
+  config = lib.mkIf config.host.builder.enable {
+    # WSL2 does not expose /dev/kvm to the guest (no nested virt by default,
+    # and Hyper-V's /dev/kvm is not bind-mounted into the WSL namespace).
+    # The default NixOS module advertises `kvm nixos-test benchmark
+    # big-parallel` as this host's system-features, which is a lie: any
+    # derivation that requires `kvm` will be dispatched here and immediately
+    # fail with "cannot open /dev/kvm". Nix selects builders by matching the
+    # derivation's required features against what the builder advertises, so
+    # the only way to keep WSL useful is to retract the features it cannot
+    # actually deliver. `nixos-test` is dropped for the same reason — it
+    # wants kvm anyway.
+    #
+    # `mkForce` because the NixOS module base-config sets a non-empty
+    # default; without force the lists would concatenate and the WSL would
+    # *still* advertise kvm.
+    nix.settings.system-features = lib.mkForce [
+      "benchmark"
+      "big-parallel"
+    ];
+
+    # Builds arrive over SSH as the user `oqyude` (see
+    # modules/server/builder.nix). On the default trusted-users = ["root"]
+    # only root can call nix-store, so the SSH session would fail to realise
+    # any .drv. Adding the SSH user to trusted-users lets the remote nix-build
+    # driver drive nix-store on the builder side. `mkForce` for the same
+    # concatenation reason as above.
+    nix.settings.trusted-users = lib.mkForce [
+      "root"
+      "oqyude"
+    ];
+
+    # The local daemon already parallelises across all 24 logical cores
+    # (max-jobs = 24 is what we measured). When acting as a builder, we
+    # want to keep that — remote builds land through SSH and the daemon
+    # serves them on top of its normal pool. No override needed; documented
+    # here so a future reader does not "tidy up" by setting max-jobs low.
+  };
+}