diff --git a/modules/nixos/base/packages.nix b/modules/nixos/base/packages.nix
index 06690166..e78be2e8 100644
--- a/modules/nixos/base/packages.nix
+++ b/modules/nixos/base/packages.nix
@@ -37,6 +37,9 @@ in
         psmisc # killall/pstree/prtstat/fuser/...
         ethtool
         pv # pipe view
+
+        # System-wide interpreter; Home Manager's python313 on desktops is a separate profile.
+        python313
       ]
       ++ lib.optionals hardwareTools.enable [
         lm_sensors # `sensors` command
diff --git a/outputs/x86_64-linux/tests/idols-aquamarine/expected.nix b/outputs/x86_64-linux/tests/idols-aquamarine/expected.nix
index b170349d..0270c4b2 100644
--- a/outputs/x86_64-linux/tests/idols-aquamarine/expected.nix
+++ b/outputs/x86_64-linux/tests/idols-aquamarine/expected.nix
@@ -20,6 +20,7 @@
   collectorFlagsUnique = true;
   inferenceUserCanRender = true;
   noHomeManager = true;
+  pythonInstalled = true;
   staticAddressMatchesWiredInterface = true;
   rootIsTmpfs = true;
   stateIsPersistent = true;
diff --git a/outputs/x86_64-linux/tests/idols-aquamarine/expr.nix b/outputs/x86_64-linux/tests/idols-aquamarine/expr.nix
index d43aa5e8..5bcdf6b8 100644
--- a/outputs/x86_64-linux/tests/idols-aquamarine/expr.nix
+++ b/outputs/x86_64-linux/tests/idols-aquamarine/expr.nix
@@ -82,6 +82,9 @@ in
 
   # Headless: no desktop session, no Home Manager.
   noHomeManager = !cfg ? home-manager.users;
+  pythonInstalled = builtins.any (
+    package: lib.hasPrefix "python3-" (package.name or "")
+  ) cfg.environment.systemPackages;
 
   # The board renames the wired NIC with the PCIe topology, so networkd matches the
   # `en*` prefix; a name-based match leaves the host without an address.