diff --git a/flake.nix b/flake.nix
index 5372b4bfd..815cb5738 100644
--- a/flake.nix
+++ b/flake.nix
@@ -110,7 +110,7 @@
               nixpkgs-fmt.enable = true;
               ruff-format = {
                 enable = true;
-                excludes = [ "rust/exo_rs/exo_rs.pyi" ];
+                excludes = [ "rust/exo_rs/python/**/*.pyi" ];
               };
               rustfmt = {
                 enable = true;
diff --git a/python/parts.nix b/python/parts.nix
index 26318c4a2..95bfcb081 100644
--- a/python/parts.nix
+++ b/python/parts.nix
@@ -46,7 +46,6 @@ let
       exoOverlay = final: prev: {
         # Replace workspace exo_rs with Nix-built wheel.
         # Preserve passthru so mkVirtualEnv can resolve dependency groups.
-        # Copy .pyi stub + py.typed marker so basedpyright can find the types.
         exo-rs = pkgs.stdenv.mkDerivation {
           pname = "exo-rs";
           version = "0.1.0";
@@ -55,12 +54,6 @@ let
           nativeBuildInputs = [ final.pyprojectWheelHook ];
           dontStrip = true;
           passthru = prev.exo-rs.passthru or { };
-
-          postInstall = ''
-            local siteDir=$out/${final.python.sitePackages}/exo_rs
-            cp ${inputs.self}/rust/exo_rs/exo_rs.pyi $siteDir/
-            touch $siteDir/py.typed
-          '';
         };
       };
       buildSystemsOverlay = final: prev:
diff --git a/rust/parts.nix b/rust/parts.nix
index 3fa8e2dab..dd7982f12 100644
--- a/rust/parts.nix
+++ b/rust/parts.nix
@@ -32,8 +32,17 @@
             isRootCargoFile =
               (baseName == "Cargo.toml" || baseName == "Cargo.lock")
               && (builtins.dirOf path == toString inputs.self);
+            isExoRsPythonSource =
+              (lib.hasInfix "/rust/exo_rs/python/" path || lib.hasSuffix "/rust/exo_rs/python" path)
+              && (
+                type == "directory"
+                || lib.hasSuffix ".py" path
+                || lib.hasSuffix ".pyi" path
+                || baseName == "py.typed"
+              );
           in
           isRootCargoFile
+          || isExoRsPythonSource
           || (inRustDir && (craneLib.filterCargoSources path type || lib.hasSuffix ".toml" path || lib.hasSuffix ".md" path));
       };