test(query): add regression coverage for react-query onMutate option (#1177)

The generated TanStack Query mutation hook exposes its `mutation` option as
`UseMutationOptions`, which includes the `onMutate` callback. Issue #1177
reported `onMutate` being missing; it is fixed on current orval but had no
regression test.

Add a compile-time consumption test that calls a generated mutation hook
with `mutation.onMutate` so a narrowed option type fails the typecheck.
Wire the existing (previously orphaned) `tests/regressions` directory into
`typecheck-generated.mjs` so these hand-written type tests run in CI.

Author: wadakatu

tests/regressions/react-query.ts

@@ -1,6 +1,7 @@
 import { keepPreviousData } from '@tanstack/react-query';
 
 import {
+  useCreatePets,
   useListPets,
   useListPetsInfinite,
 } from '../generated/react-query/mutator/endpoints';
@@ -40,3 +41,22 @@ export const useHookWithPlaceHolderData = () => {
 
   return names;
 };
+
+// Regression test for https://github.com/orval-labs/orval/issues/1177
+//
+// The generated TanStack Query mutation hook must accept an `onMutate`
+// callback through its `mutation` option. `onMutate` is part of TanStack's
+// `UseMutationOptions`; if orval ever narrows that option type (as it did when
+// #1177 was filed), this function stops compiling and fails the typecheck.
+export const useCreatePetsWithOnMutate = () =>
+  useCreatePets({
+    mutation: {
+      onMutate: (variables) => {
+        // `variables` must be the typed mutation input, not `any`.
+        void variables.data;
+        // @ts-expect-error - a key absent from the mutation input must error;
+        // this proves `variables` is strongly typed (not `any`).
+        void variables.notAField;
+      },
+    },
+  });

tests/scripts/typecheck-generated.mjs

@@ -34,7 +34,10 @@ for (const folder of folders) {
 
   const config = {
     extends: './tsconfig.json',
-    include: [`generated/${folder}`, 'mutators'],
+    // `regressions` holds hand-written compile-time tests that import generated
+    // code and exercise its public types (e.g. the #1177 onMutate regression),
+    // so a narrowed option type fails the typecheck.
+    include: [`generated/${folder}`, 'mutators', 'regressions'],
   };
 
   // Bun's flat node_modules makes the MCP SDK resolve `zod` to the project's v3.25