test(e2e): fail tests when ZodError appears in browser console

e2e/utils/localTestFixture.ts

@@ -176,7 +176,33 @@ export const test = base.extend<ScenarioFixtures & { localConfig: LocalConfig },
     { scope: 'test' },
   ],
 
-  page: async ({ page, localConfig, scenario }, use) => {
+  page: async ({ page, localConfig, scenario }, use, testInfo) => {
+    // Watch the browser console + page errors for `ZodError` strings.
+    // `@gusto/embedded-api` validates every response with Zod; when the
+    // backend ships a shape that disagrees with the published schema the
+    // request rejects and surfaces as a `ZodError` in the browser console
+    // (either as an uncaught page error or via React's error-boundary
+    // `console.error`). Tests can otherwise pass while the SDK is silently
+    // crashing into an error boundary mid-flow, so we fail the test if any
+    // such error fires during its lifetime.
+    const zodErrors: string[] = []
+
+    const recordIfZodError = (source: 'console' | 'pageerror', text: string) => {
+      if (text.includes('ZodError')) {
+        zodErrors.push(`[${source}] ${text}`)
+      }
+    }
+
+    page.on('console', msg => {
+      if (msg.type() !== 'error' && msg.type() !== 'warning') return
+      recordIfZodError('console', msg.text())
+    })
+
+    page.on('pageerror', err => {
+      const text = err.stack ?? `${err.name}: ${err.message}`
+      recordIfZodError('pageerror', text)
+    })
+
     const originalGoto = page.goto.bind(page)
 
     page.goto = async (url: string, options?: Parameters<typeof page.goto>[1]) => {
@@ -236,6 +262,25 @@ export const test = base.extend<ScenarioFixtures & { localConfig: LocalConfig },
     }
 
     await use(page)
+
+    if (zodErrors.length > 0) {
+      const detail = zodErrors.join('\n\n---\n\n')
+      await testInfo.attach('zod-errors.txt', {
+        body: detail,
+        contentType: 'text/plain',
+      })
+      // Only fail the test if it would otherwise pass — if it already
+      // failed for another reason, surface the Zod errors as an
+      // attachment but don't overwrite the existing failure.
+      if (testInfo.status === 'passed' || testInfo.status === undefined) {
+        throw new Error(
+          `Detected ${zodErrors.length} ZodError(s) in the browser console during this test. ` +
+            `This means the backend returned a response shape that disagrees with the ` +
+            `@gusto/embedded-api Zod schema. See the zod-errors.txt attachment for the full text.\n\n` +
+            detail,
+        )
+      }
+    }
   },
 })