diff --git a/packages/engine/src/external-dependencies.ts b/packages/engine/src/external-dependencies.ts
index 6cee2dd..1b661a3 100644
--- a/packages/engine/src/external-dependencies.ts
+++ b/packages/engine/src/external-dependencies.ts
@@ -67,7 +67,9 @@ const PYTHON_STDLIB_ROOTS = new Set([
   "tempfile",
   "threading",
   "time",
+  "tomllib",
   "traceback",
+  "types",
   "typing",
   "unittest",
   "urllib",
diff --git a/tests/external-dependencies-regression.test.mjs b/tests/external-dependencies-regression.test.mjs
new file mode 100644
index 0000000..41748ce
--- /dev/null
+++ b/tests/external-dependencies-regression.test.mjs
@@ -0,0 +1,20 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { isPythonStdlibSpecifier } from "../packages/engine/dist/external-dependencies.js";
+
+test("Python stdlib detection recognizes common Python 3.12 modules", () => {
+  assert.equal(isPythonStdlibSpecifier("hashlib"), true);
+  assert.equal(isPythonStdlibSpecifier("types"), true);
+  assert.equal(isPythonStdlibSpecifier("tomllib"), true);
+  assert.equal(isPythonStdlibSpecifier("types.SimpleNamespace"), true);
+  assert.equal(isPythonStdlibSpecifier("tomllib.loads"), true);
+});
+
+test("Python stdlib detection does not classify third-party imports as stdlib", () => {
+  assert.equal(isPythonStdlibSpecifier("requests"), false);
+  assert.equal(isPythonStdlibSpecifier("pydantic"), false);
+  assert.equal(isPythonStdlibSpecifier("toml"), false);
+  assert.equal(isPythonStdlibSpecifier(".") , false);
+  assert.equal(isPythonStdlibSpecifier("..local_module"), false);
+});