[Inference UI] Add scout tests for feature settings page (elastic#261790)

## Summary

Adds Scout tests for the Feature Settings (Model Settings) page under
Stack Management. This page allows users to configure default AI models
and manage per-feature inference endpoint assignments.

### How to run the tests

```
node scripts/scout.js start-server --arch stateful --domain classic
npx playwright test --config .../test/scout/ui/playwright.config.ts --project local --headed feature_settings.spec
```

### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [x] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [x] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)
- [x] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

### Identify risks

Does this PR introduce any risks? For example, consider risks like hard
to test bugs, performance regression, potential of data loss.

Describe the risk, its severity, and mitigation for each identified
risk. Invite stakeholders and evaluate how to proceed before merging.

- [ ] [See some risk
examples](https://github.com/elastic/kibana/blob/main/RISK_MATRIX.mdx)
- [ ] ...

Author: saikatsarkar056

.agents/skills/scout-ui-testing/SKILL.md

@@ -38,10 +38,14 @@ description: Use when creating, updating, debugging, or reviewing Scout UI tests
 ## Page objects (UI)
 
 - Prefer `page.testSubj.locator(...)`, role/label locators; avoid brittle CSS.
-- Keep selectors + interactions inside the page object class.
+- Keep selectors + interactions inside the page object class. **Do not use `expect` assertions in page objects** — use `waitForSelector` for waiting on elements. Assertions belong in test specs only.
+- **Keep route mocks out of page objects** — page objects are for UI interactions only. Put `page.route()` mocks in a dedicated `fixtures/mocks.ts` file as standalone functions that accept `page` as a parameter. See `cloud_security_posture/test/scout_cspm_agentless/ui/fixtures/mocks.ts` for the reference pattern.
 - Don't make API calls from page objects (use `apiServices`/`kbnClient` in hooks instead).
 - Register plugin page objects by extending the `pageObjects` fixture in `test/scout*/ui/fixtures/index.ts`.
+- **Use `readonly` class fields for static locators** — assign them in the constructor, not as getter methods. Use methods only for parameterized locators/actions. See `DashboardApp` in `kbn-scout` for the reference pattern.
 - Scout provides EUI component wrappers for stable interactions with common EUI widgets: `EuiComboBoxWrapper`, `EuiDataGridWrapper`, `EuiSelectableWrapper`, `EuiCheckBoxWrapper`, `EuiFieldTextWrapper`, `EuiCodeBlockWrapper`, `EuiSuperSelectWrapper`, `EuiToastWrapper`. Import them from `@kbn/scout` and use them as class members in page objects.
+- **Avoid `.first()`, `.nth()`, `.last()`** — the `playwright/no-nth-methods` lint rule flags these. Instead, use `data-test-subj` attributes or other targeted selectors. If the component lacks a `data-test-subj`, add one rather than disabling the rule.
+- **Do not disable eslint rules** — avoid `eslint-disable` comments in test files. Fix the underlying issue (e.g., use targeted selectors instead of positional ones, add `data-test-subj` to the components) rather than suppressing the lint rule.
 
 ## Parallel UI specifics (spaceTest)
 

.buildkite/scout_ci_config.yml

@@ -35,6 +35,7 @@ plugins:
     - saved_objects_management
     - search_getting_started
     - search_homepage
+    - search_inference_endpoints
     - security
     - security_solution
     - share

.github/CODEOWNERS

@@ -1200,6 +1200,7 @@ x-pack/platform/test/plugin_api_perf/plugins/task_manager_performance @elastic/r
 x-pack/platform/test/reporting_api_integration/plugins/reporting_fixture @elastic/response-ops
 x-pack/platform/test/reporting_api_integration/plugins/reporting_test_routes @elastic/response-ops
 x-pack/platform/test/saved_object_api_integration/common/plugins/saved_object_test_plugin @elastic/kibana-security
+x-pack/platform/test/search_inference_endpoints/plugins/search_inference_endpoints_fixture @elastic/search-kibana
 x-pack/platform/test/security_api_integration/packages/helpers @elastic/kibana-security
 x-pack/platform/test/security_api_integration/plugins/audit_log @elastic/kibana-security
 x-pack/platform/test/security_api_integration/plugins/features_provider @elastic/kibana-security

package.json

@@ -999,6 +999,7 @@
     "@kbn/search-homepage": "link:x-pack/solutions/search/plugins/search_homepage",
     "@kbn/search-index-documents": "link:x-pack/platform/packages/shared/kbn-search-index-documents",
     "@kbn/search-inference-endpoints": "link:x-pack/platform/plugins/shared/search_inference_endpoints",
+    "@kbn/search-inference-endpoints-fixture-plugin": "link:x-pack/platform/test/search_inference_endpoints/plugins/search_inference_endpoints_fixture",
     "@kbn/search-navigation": "link:x-pack/solutions/search/plugins/search_navigation",
     "@kbn/search-notebooks": "link:x-pack/solutions/search/plugins/search_notebooks",
     "@kbn/search-playground": "link:x-pack/solutions/search/plugins/search_playground",

src/platform/packages/shared/kbn-scout/src/servers/configs/config_sets/inference_test/serverless/search.serverless.config.ts

@@ -0,0 +1,26 @@
+/*
+ * 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 { resolve } from 'path';
+import { REPO_ROOT } from '@kbn/repo-info';
+import { servers as defaultConfig } from '../../default/serverless/search.serverless.config';
+import type { ScoutServerConfig } from '../../../../../types';
+
+const pluginPath = `--plugin-path=${resolve(
+  REPO_ROOT,
+  'x-pack/platform/test/search_inference_endpoints/plugins/search_inference_endpoints_fixture'
+)}`;
+
+export const servers: ScoutServerConfig = {
+  ...defaultConfig,
+  kbnTestServer: {
+    ...defaultConfig.kbnTestServer,
+    serverArgs: [...defaultConfig.kbnTestServer.serverArgs, pluginPath],
+  },
+};

src/platform/packages/shared/kbn-scout/src/servers/configs/config_sets/inference_test/stateful/classic.stateful.config.ts

@@ -0,0 +1,26 @@
+/*
+ * 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 { resolve } from 'path';
+import { REPO_ROOT } from '@kbn/repo-info';
+import type { ScoutServerConfig } from '../../../../../types';
+import { defaultConfig } from '../../default/stateful/base.config';
+
+const pluginPath = `--plugin-path=${resolve(
+  REPO_ROOT,
+  'x-pack/platform/test/search_inference_endpoints/plugins/search_inference_endpoints_fixture'
+)}`;
+
+export const servers: ScoutServerConfig = {
+  ...defaultConfig,
+  kbnTestServer: {
+    ...defaultConfig.kbnTestServer,
+    serverArgs: [...defaultConfig.kbnTestServer.serverArgs, pluginPath],
+  },
+};

tsconfig.base.json

@@ -2042,6 +2042,8 @@
       "@kbn/search-index-documents/*": ["x-pack/platform/packages/shared/kbn-search-index-documents/*"],
       "@kbn/search-inference-endpoints": ["x-pack/platform/plugins/shared/search_inference_endpoints"],
       "@kbn/search-inference-endpoints/*": ["x-pack/platform/plugins/shared/search_inference_endpoints/*"],
+      "@kbn/search-inference-endpoints-fixture-plugin": ["x-pack/platform/test/search_inference_endpoints/plugins/search_inference_endpoints_fixture"],
+      "@kbn/search-inference-endpoints-fixture-plugin/*": ["x-pack/platform/test/search_inference_endpoints/plugins/search_inference_endpoints_fixture/*"],
       "@kbn/search-navigation": ["x-pack/solutions/search/plugins/search_navigation"],
       "@kbn/search-navigation/*": ["x-pack/solutions/search/plugins/search_navigation/*"],
       "@kbn/search-notebooks": ["x-pack/solutions/search/plugins/search_notebooks"],

x-pack/platform/plugins/shared/search_inference_endpoints/moon.yml

@@ -53,6 +53,7 @@ dependsOn:
   - '@kbn/inference-common'
   - '@kbn/inference-plugin'
   - '@kbn/management-settings-ids'
+  - '@kbn/scout'
 tags:
   - plugin
   - prod
@@ -65,6 +66,7 @@ fileGroups:
     - common/**/*
     - public/**/*
     - server/**/*
+    - test/scout_inference_test/**/*
     - '!target/**/*'
   jest-config:
     - jest.config.js

x-pack/platform/plugins/shared/search_inference_endpoints/public/components/settings/add_model_popover.tsx

@@ -104,6 +104,7 @@ export const AddModelPopover: React.FC<AddModelPopoverProps> = ({
         onChange={handleChange}
         singleSelection
         searchable
+        data-test-subj="add-model-selectable"
         searchProps={{
           placeholder: i18n.translate('xpack.searchInferenceEndpoints.settings.addModel.search', {
             defaultMessage: 'Search models...',

x-pack/platform/plugins/shared/search_inference_endpoints/test/scout_inference_test/ui/fixtures/index.ts

@@ -0,0 +1,36 @@
+/*
+ * 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; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import type { PageObjects, ScoutTestFixtures, ScoutWorkerFixtures } from '@kbn/scout';
+import { test as baseTest, createLazyPageObject } from '@kbn/scout';
+import { FeatureSettingsPage } from './page_objects';
+
+export interface ExtScoutTestFixtures extends ScoutTestFixtures {
+  pageObjects: PageObjects & {
+    featureSettings: FeatureSettingsPage;
+  };
+}
+
+export const test = baseTest.extend<ExtScoutTestFixtures, ScoutWorkerFixtures>({
+  pageObjects: async (
+    {
+      pageObjects,
+      page,
+    }: {
+      pageObjects: ExtScoutTestFixtures['pageObjects'];
+      page: ExtScoutTestFixtures['page'];
+    },
+    use: (pageObjects: ExtScoutTestFixtures['pageObjects']) => Promise<void>
+  ) => {
+    const extendedPageObjects = {
+      ...pageObjects,
+      featureSettings: createLazyPageObject(FeatureSettingsPage, page),
+    };
+
+    await use(extendedPageObjects);
+  },
+});