fix(open-api#ts-client): address review feedback

- rewriteConstToEnum now uses the cloneDeepWith customiser pattern that
  the rest of normalise.ts follows, returning a new spec tree instead of
  mutating in place.
- Tighten the FastAPI const regression test: assert the concrete current
  shape (kind: string via the languages.ts defence-in-depth) so any
  future tightening that restores the Literal narrowing is a deliberate,
  visible change rather than silently accepted.

Author: nx-plugin-for-aws

packages/nx-plugin/src/open-api/ts-client/generator.composite-types.spec.ts

@@ -1265,14 +1265,18 @@ describe('openApiTsClientGenerator - composite schemas', () => {
 
     // Phantom references synthesised from `const` must not leak through.
     // Previously the const shape caused hey-api-openapi to reference a
-    // non-existent `_String` (or `Kind`) type, breaking tsc in strict mode.
+    // non-existent `_String` type, breaking tsc in strict mode.
     expect(types).not.toMatch(/\b_String\b/);
     expect(client).not.toMatch(/\b_String\b/);
     expect(types).not.toMatch(/:\s*undefined\b/);
 
-    // Circle.kind should resolve to something tsc can type-check (either the
-    // literal 'circle' or bare string with the defence-in-depth fix).
-    expect(types).toMatch(/kind:\s*('circle'|"circle"|string|Kind\b)/);
+    // After rewriteConstToEnum + languages.ts defence-in-depth the property
+    // resolves to bare `string` (the generator does not currently propagate
+    // the literal back to the reference site — it's compiled cleanly by tsc
+    // but loses the Literal narrowing). Assert the concrete current shape so
+    // any future tightening of this path is a deliberate, visible change.
+    expect(types).toMatch(/kind:\s*string\b/);
+    expect(types).not.toMatch(/kind:\s*'circle'/);
 
     expect(types).toMatchSnapshot();
     expect(client).toMatchSnapshot();

packages/nx-plugin/src/open-api/utils/normalise.ts

@@ -265,24 +265,19 @@ const hoistInlineObjectSubSchemas = (
  * downstream hey-api/openapi-ts handles the enum shape but synthesises
  * phantom named references for the const shape.
  */
-const rewriteConstToEnum = (spec: Spec): Spec => {
-  const walk = (obj: any): void => {
-    if (!obj || typeof obj !== 'object') {
-      return;
-    }
-    if (Array.isArray(obj)) {
-      obj.forEach(walk);
-      return;
-    }
-    if ('const' in obj && !('enum' in obj)) {
-      obj.enum = [obj.const];
-      delete obj.const;
+const rewriteConstToEnum = (spec: Spec): Spec =>
+  cloneDeepWith(spec, (v) => {
+    if (
+      v &&
+      typeof v === 'object' &&
+      !Array.isArray(v) &&
+      'const' in v &&
+      !('enum' in v)
+    ) {
+      const { const: constValue, ...rest } = v;
+      return cloneDeepWith({ ...rest, enum: [constValue] });
     }
-    Object.values(obj).forEach(walk);
-  };
-  walk(spec);
-  return spec;
-};
+  });
 
 /**
  * In order to ensure we generate models consistently whether or not users used refs or inline schemas,