chore(aquamarine): use NixOS's NPU module with nixos-unstable-small (#527)

* chore(aquamarine): take the NPU stack from nixos-unstable-small
* refactor(aquamarine): load the NPU driver via hardware.cpu.intel.npu

Assisted-by: DeepSeek Harness (claude-opus-5-5)

hosts/idols-aquamarine/asr.nix

@@ -3,7 +3,7 @@
   mylib,
   myvars,
   pkgs,
-  pkgs-npu,
+  pkgs-small,
   ...
 }:
 let
@@ -52,9 +52,9 @@ let
   '';
 
   # openvino-genai 2026.4.0.0 fails to compile against the OpenVINO headers in
-  # nixos-unstable (no matching constructor in continuous_batching); the branch's
-  # nixpkgs builds it, and the service has to match the NPU stack anyway.
-  pythonEnv = pkgs-npu.python3.withPackages (ps: [
+  # nixos-unstable (no matching constructor in continuous_batching); the
+  # service takes it from the same nixpkgs as the NPU stack.
+  pythonEnv = pkgs-small.python3.withPackages (ps: [
     ps.fastapi
     ps.numpy
     ps.openvino-genai
@@ -90,9 +90,6 @@ in
       # Python block-buffers stdout when it is not a tty, which would hold the
       # request log lines back instead of putting them in the journal.
       PYTHONUNBUFFERED = "1";
-      # The stock driver cannot find the NPU compiler; the patched one loads it
-      # from its own store path.
-      ZE_ENABLE_ALT_DRIVERS = "${lib.getLib pkgs-npu.intel-npu-driver}/lib/libze_intel_npu.so";
     };
 
     # Reads its model, writes its cache, uses the NPU and listens on the LAN.

hosts/idols-aquamarine/default.nix

@@ -1,8 +1,6 @@
 {
   disko,
   myvars,
-  lib,
-  pkgs-npu,
   ...
 }:
 #############################################################
@@ -71,13 +69,6 @@ in
   # profile's rootless Podman (modules/nixos/agent.nix), built from the `~/src`
   # checkout that ./preservation.nix keeps.
 
-  # Speech recognition runs on the NPU, see ./asr.nix. The driver and the
-  # compiler it loads come from NixOS/nixpkgs#570230, which is unmerged, so they
-  # are taken from that branch as `pkgs-npu`; the stock driver cannot find the
-  # compiler, the patched one loads it from its own store path. The service sets
-  # this itself -- the session variable is for manual runs.
-  environment.sessionVariables.ZE_ENABLE_ALT_DRIVERS = "${lib.getLib pkgs-npu.intel-npu-driver}/lib/libze_intel_npu.so";
-
   # The daemons of the hosts that build here (modules/nixos/base/remote-builders.nix).
   # Their host keys have no passphrase, so they only get the daemon protocol, as
   # nix.sshServe does. `--store daemon` hands builds to the system daemon instead

hosts/idols-aquamarine/hardware-intel-cpu.nix

@@ -1,8 +1,14 @@
 {
   pkgs,
+  pkgs-small,
   ...
 }:
 {
+  # The NPU serves ./asr.nix; the driver's compiler lookup is fixed by
+  # NixOS/nixpkgs#570230, which reached nixos-unstable-small first (WA-037).
+  hardware.cpu.intel.npu.enable = true;
+  nixpkgs.overlays = [ (_: _: { inherit (pkgs-small) intel-npu-driver; }) ];
+
   # Ad-hoc CPU idle-power diagnostics: package power, C-state residency and
   # wakeup attribution. Long-term RAPL export lives in the shared
   # modules/nixos/base/power-monitoring.nix module.