[ResponseOps][Alerting v2] Use isFetching instead of isLoading in episode assignee filter (elastic#273019)

## 📄 Summary

> [!important]
> Alerting v2 work under feature flag disabled by default. See 🧪
Verification steps > ⚙️ Environment Setup for more information.

- Switches from `isLoading` to `isFetching` in the `useBulkGetProfiles`
query to avoid showing an infinite loading state when the query is
disabled (when no episode in the table has an assignee and no textual
search is performed)

<details>
<summary>

## 🧪 Verification steps

</summary>

### ⚙️ Environment Setup

Add the following flag to your `kibana.dev.yml` to enable alerting v2:

```yaml
xpack.alerting_v2.enabled: true
```

### ✅ Happy Path

1. Create one or more v2 rules that fire alert episodes
2. Navigate to the Episodes list page
3. Open the filter by assignee
4. Verify that it shows an empty state instead of loading

### ⚡️ Edge Cases

- Open the empty filter, then start typing a name and verify that the
popover shows the user's name
- Assign an episode to a user and verify that the filter by assignee
shows the user's name

</details>

## ⏪ Backport rationale

Pre-GA alerting v2 work, not backporting

## 🔗 References

Fixes elastic/rna-program#571

## ☑️ Checklist

- [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
- [x] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

Author: umbopepato

x-pack/platform/packages/shared/response-ops/alerting-v2-episodes-ui/components/filters/assignee_filter.test.tsx

@@ -28,17 +28,14 @@ jest.mock('../../hooks/use_bulk_get_profiles', () => ({
 const mockUseBulkGetProfiles = jest.mocked(useBulkGetProfilesModule.useBulkGetProfiles);
 const InlineFilterPopoverSpy = jest.spyOn(inlineFilterPopoverModule, 'InlineFilterPopover');
 
-mockUseBulkGetProfiles.mockReturnValue({
-  data: [
-    {
-      uid: 'uid-alice',
-      user: { full_name: 'Alice Smith', email: 'alice@example.com', username: 'alice' },
-    },
-    { uid: 'uid-bob', user: { full_name: '', email: 'bob@example.com', username: 'bob' } },
-    { uid: 'uid-charlie', user: { full_name: '', email: '', username: 'charlie' } },
-  ],
-  isLoading: false,
-} as unknown as ReturnType<typeof useBulkGetProfilesModule.useBulkGetProfiles>);
+const mockProfiles = [
+  {
+    uid: 'uid-alice',
+    user: { full_name: 'Alice Smith', email: 'alice@example.com', username: 'alice' },
+  },
+  { uid: 'uid-bob', user: { full_name: '', email: 'bob@example.com', username: 'bob' } },
+  { uid: 'uid-charlie', user: { full_name: '', email: '', username: 'charlie' } },
+];
 
 describe('AlertEpisodesAssigneeFilter', () => {
   const defaultProps = {
@@ -52,6 +49,11 @@ describe('AlertEpisodesAssigneeFilter', () => {
 
   beforeEach(() => {
     jest.clearAllMocks();
+    mockUseBulkGetProfiles.mockReturnValue({
+      data: mockProfiles,
+      isFetching: false,
+      isLoading: false,
+    } as unknown as ReturnType<typeof useBulkGetProfilesModule.useBulkGetProfiles>);
   });
 
   const openPopover = () => user.click(screen.getByTestId('test-assignee-filter-button'));
@@ -129,4 +131,20 @@ describe('AlertEpisodesAssigneeFilter', () => {
       {}
     );
   });
+
+  it('does not show a loading state when the query is disabled (isFetching is false even if isLoading is true)', async () => {
+    // When assigneeUids is empty, react-query disables the query: isLoading is true
+    // (never fetched) but isFetching is false (nothing is actively fetching).
+    // The component must use isFetching, not isLoading, to avoid an infinite loading state.
+    mockUseBulkGetProfiles.mockReturnValue({
+      data: [],
+      isFetching: false,
+      isLoading: true,
+    } as unknown as ReturnType<typeof useBulkGetProfilesModule.useBulkGetProfiles>);
+
+    render(<AlertEpisodesAssigneeFilter {...defaultProps} assigneeUids={[]} />);
+    await openPopover();
+
+    expect(screen.queryByRole('progressbar')).not.toBeInTheDocument();
+  });
 });

x-pack/platform/packages/shared/response-ops/alerting-v2-episodes-ui/components/filters/assignee_filter.tsx

@@ -30,7 +30,9 @@ export function AlertEpisodesAssigneeFilter({
   const [isOpen, setIsOpen] = useState(false);
   const [search, setSearch] = useState('');
 
-  const { data: profiles = [], isLoading } = useBulkGetProfiles({
+  // Here we use `isFetching` instead of `isLoading` to avoid showing an infinite loading state when
+  // the query is disabled (when no episode in the table has an assignee and no textual search is performed)
+  const { data: profiles = [], isFetching } = useBulkGetProfiles({
     userProfile,
     uids: assigneeUids,
     toasts: notifications.toasts,
@@ -91,7 +93,7 @@ export function AlertEpisodesAssigneeFilter({
         onSearchChange={setSearch}
         searchPlaceholder={i18n.ASSIGNEE_FILTER_SEARCH_PLACEHOLDER}
         emptyMessage={i18n.ASSIGNEE_FILTER_NO_MATCH}
-        isLoading={isLoading}
+        isLoading={isFetching}
         data-test-subj={`${dataTestSubj}-popover`}
       />
     </EuiPopover>