[SharedUX] Migrate error boundary example plugin FTRs to Scout (elastic#268647)

Relates to elastic/kibana-team#2818

## Summary

- Migrated the Error Boundary example plugin FTR tests to Scout as part
of SharedUX's OnWeek initiative to migrate all SharedUX owned FTR tests
to Scout, improving CI costs and execution time.
- Migrated 2 FTR tests from `src/platform/test/examples/error_boundary/`
to Scout at `examples/error_boundary/test/scout_examples/ui/`
- Removed the FTR test file and its `loadTestFile` entry from
`src/platform/test/examples/config.js`
- Added `error_boundary_example` to `.buildkite/scout_ci_config.yml` for
CI discovery
- Updated `tsconfig.json` and regenerated `moon.yml` to include Scout
test paths and `@kbn/scout` dependency
- Used the `scout-migrate-from-ftr` skill to plan and execute the
migration, and `scout-best-practices-reviewer` to validate parity and
best practices compliance.

### Validation
- Tests pass locally against Scout `examples` server config set
- Ran `--repeat-each 30` to verify no flakiness
<img width="1011" height="430" alt="Screenshot 2026-05-11 at 12 18 24"
src="https://github.com/user-attachments/assets/21cab279-493b-4a16-8e39-ed65520d95a3"
/>

Author: angeles-mb

.buildkite/scout_ci_config.yml

@@ -18,6 +18,7 @@ plugins:
     - discover
     - discover_enhanced
     - entity_store
+    - error_boundary_example
     - exploratory_view
     - fleet
     - flyoutSystemExamples

examples/error_boundary/moon.yml

@@ -21,6 +21,7 @@ dependsOn:
   - '@kbn/developer-examples-plugin'
   - '@kbn/shared-ux-error-boundary'
   - '@kbn/shared-ux-page-kibana-template'
+  - '@kbn/scout'
 tags:
   - plugin
   - prod
@@ -32,5 +33,6 @@ fileGroups:
     - common/**/*.ts
     - public/**/*.ts
     - public/**/*.tsx
+    - test/scout_examples/**/*
     - '!target/**/*'
 tasks: {}

examples/error_boundary/test/scout_examples/ui/playwright.config.ts

@@ -0,0 +1,14 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import { createPlaywrightConfig } from '@kbn/scout';
+
+export default createPlaywrightConfig({
+  testDir: './tests',
+});

examples/error_boundary/test/scout_examples/ui/tests/error_boundary.spec.ts

@@ -0,0 +1,47 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+import { test } from '@kbn/scout';
+import { expect } from '@kbn/scout/ui';
+
+test.describe('Error Boundary Examples', { tag: ['@local-stateful-classic'] }, () => {
+  test.beforeEach(async ({ browserAuth, page }) => {
+    await browserAuth.loginAsViewer();
+    await page.gotoApp('errorBoundaryExample');
+    await expect(page.testSubj.locator('errorBoundaryExampleHeader')).toBeVisible();
+  });
+
+  test('fatal error shows error boundary and recovers on reload', async ({ page }) => {
+    await page.testSubj.locator('fatalErrorBtn').click();
+
+    await expect(page.testSubj.locator('errorBoundaryFatalHeader')).toBeVisible();
+    await expect(page.testSubj.locator('errorBoundaryExampleHeader')).toHaveCount(0);
+
+    await page.testSubj.locator('errorBoundaryFatalShowDetailsBtn').click();
+    await expect(page.testSubj.locator('errorBoundaryFatalDetailsErrorString')).toContainText(
+      'Error: Example of unknown error type'
+    );
+
+    await page.testSubj.locator('euiFlyoutCloseButton').click();
+    await page.testSubj.locator('errorBoundaryFatalPromptReloadBtn').click();
+
+    await expect(page.testSubj.locator('errorBoundaryExampleHeader')).toBeVisible();
+  });
+
+  test('recoverable error shows error boundary and recovers on reload', async ({ page }) => {
+    await page.testSubj.locator('recoverableErrorBtn').click();
+
+    await expect(page.testSubj.locator('errorBoundaryRecoverableHeader')).toBeVisible();
+    await expect(page.testSubj.locator('errorBoundaryExampleHeader')).toHaveCount(0);
+
+    await page.testSubj.locator('errorBoundaryRecoverablePromptReloadBtn').click();
+
+    await expect(page.testSubj.locator('errorBoundaryExampleHeader')).toBeVisible();
+  });
+});

examples/error_boundary/tsconfig.json

@@ -8,6 +8,7 @@
     "common/**/*.ts",
     "public/**/*.ts",
     "public/**/*.tsx",
+    "test/scout_examples/**/*",
     "../../typings/**/*"
   ],
   "exclude": [
@@ -17,6 +18,7 @@
     "@kbn/core",
     "@kbn/developer-examples-plugin",
     "@kbn/shared-ux-error-boundary",
-    "@kbn/shared-ux-page-kibana-template"
+    "@kbn/shared-ux-page-kibana-template",
+    "@kbn/scout"
   ]
 }

src/platform/test/examples/config.js

@@ -32,7 +32,6 @@ export default async function ({ readConfigFile }) {
       require.resolve('./unified_field_list_examples'),
       require.resolve('./unified_tabs_examples'),
       require.resolve('./discover_customization_examples'),
-      require.resolve('./error_boundary'),
       require.resolve('./response_stream'),
       require.resolve('./esql_ux_example'),
     ],