M8-R18: stabilize Mantine frontend tests

frontend/src/test-utils.test.tsx

@@ -0,0 +1,16 @@
+import { screen } from '@testing-library/react'
+import { useMantineEnv } from '@mantine/core'
+import { describe, expect, it } from 'vitest'
+import { renderWithProviders } from './test-utils'
+
+function MantineEnvironmentProbe() {
+  return <output>{useMantineEnv()}</output>
+}
+
+describe('renderWithProviders', () => {
+  it('uses Mantine test environment', () => {
+    renderWithProviders(<MantineEnvironmentProbe />)
+
+    expect(screen.getByText('test')).toBeInTheDocument()
+  })
+})

frontend/src/test-utils.tsx

@@ -51,7 +51,7 @@ export function renderWithProviders(ui: ReactNode, options: RenderOptions = {})
 
   function Wrapper() {
     return (
-      <MantineProvider>
+      <MantineProvider env="test">
         <QueryClientProvider client={queryClient}>
           <MemoryRouter initialEntries={entries}>
             <Routes>

frontend/vite.config.ts

@@ -19,6 +19,9 @@ export default defineConfig({
   test: {
     environment: 'jsdom',
     globals: true,
+    // Mantine-heavy UI tests allocate substantial jsdom resources. Keep the
+    // worker pool bounded so concurrent CI jobs remain reliable.
+    maxWorkers: 2,
     setupFiles: ['./src/test-setup.ts'],
     env: {
       // Lock the test timezone to UTC so that date-formatting assertions