refactor(test): add scenario.md and restructure stale update rejection test (#4019)

## Description

This PR finalises the manual test coverage for the
`rejectStaleNavStateUpdates` prop on `TabsHost` and the companion
`onTabSelectionRejected` callback. The existing single-file test screen
(`test-tabs-stale-update-rejection.tsx`) is promoted to a
directory-based module so that a `scenario.md` can live alongside the
implementation, following the established pattern for tab test scenarios
in this repo.

The scenario covers three distinct cases: baseline state verification,
stale rejection triggered by a heavy render race, and runtime toggling
of `rejectStaleNavStateUpdates` to confirm the prop controls rejection
behaviour dynamically. Both iOS (18.x and 26.x) and Android (API 36) are
listed as supported platforms. An automated E2E Detox test is noted as
planned but intentionally deferred.

The toast message on `onTabSelectionRejected` is also simplified from a
JSON-stringified payload snippet to the plain string
`onTabSelectionRejected`, making future test assertions straightforward.

Closes:
software-mansion/react-native-screens-labs#1456

## Changes

- **Tests/Tabs**: Converted `test-tabs-stale-update-rejection.tsx` from
a flat file to a directory module
(`test-tabs-stale-update-rejection/index.tsx`) and fixed all relative
import paths accordingly
- **Tests/Tabs**: Simplified the `onTabSelectionRejected` toast message
from a JSON-stringified event excerpt to the literal string
`onTabSelectionRejected` for easier test assertions
- **Tests/Tabs**: Added `scenario.md` with a full 7-step manual test
plan covering baseline, stale rejection under heavy render, and runtime
toggling of `rejectStaleNavStateUpdates`

Author: LKuchno

…abs/test-tabs-stale-update-rejection.tsx …st-tabs-stale-update-rejection/index.tsxapps/src/tests/single-feature-tests/tabs/test-tabs-stale-update-rejection.tsx renamed to apps/src/tests/single-feature-tests/tabs/test-tabs-stale-update-rejection/index.tsx apps/src/tests/single-feature-tests/tabs/test-tabs-stale-update-rejection.tsx renamed to apps/src/tests/single-feature-tests/tabs/test-tabs-stale-update-rejection/index.tsx

@@ -8,9 +8,9 @@ import {
   useTabsNavigationContext,
   TabsContainerWithHostConfigContext,
   useTabsHostConfig,
-} from '../../../shared/gamma/containers/tabs';
-import { CenteredLayoutView } from '../../../shared/CenteredLayoutView';
-import { ToastProvider, useToast } from '../../../shared/';
+} from '@apps/shared/gamma/containers/tabs';
+import { CenteredLayoutView } from '@apps/shared/CenteredLayoutView';
+import { ToastProvider, useToast } from '@apps/shared';
 import { Colors } from '@apps/shared/styling';
 
 const scenarioDescription: ScenarioDescription = {
@@ -116,7 +116,7 @@ function AppContents() {
           2,
         )}`;
         console.warn(message);
-        toast.push({ message: message, backgroundColor: Colors.GreenLight60 });
+        toast.push({ message: `onTabSelectionRejected: ${event.nativeEvent.rejectedScreenKey}`, backgroundColor: Colors.GreenLight60 });
       }}
     />
   );
@@ -143,7 +143,7 @@ function HeavyRenderHierarchy({
 
 function blockThread(ms: number) {
   const end = Date.now() + ms;
-  while (Date.now() < end) {}
+  while (Date.now() < end) { }
 }
 
 export default createScenario(App, scenarioDescription);

apps/src/tests/single-feature-tests/tabs/test-tabs-stale-update-rejection/scenario.md

@@ -0,0 +1,87 @@
+# Test Scenario: Stale update rejection
+
+## Details
+
+**Description:** Verifies the `rejectStaleNavStateUpdates` prop on `TabsHost`
+and the `onTabSelectionRejected` callback that fires when the native container
+rejects a navigation state update. When `rejectStaleNavStateUpdates` is `true`,
+the native side rejects any state update whose provenance baseline has been
+superseded - meaning a newer state of a different origin
+was committed before the JS update reached the UI thread. Each rejection fires
+`onTabSelectionRejected` with a `TabSelectionRejectedEvent` payload.
+
+**OS test creation version:** iOS: 18.6 and 26.4, Android: API Level 36.
+
+## E2E test
+
+Other: Planned, but will be implemented separately after research.
+
+## Prerequisites
+
+- iOS device or simulator
+- Android emulator
+
+## Note
+
+- A toast labeled `onTabSelectionRejected` appears at the bottom of the
+  screen whenever the callback fires.
+- `heavyRender` is per-tab state. Toggling it on a given tab blocks the
+  JS thread for 3 000 ms on every render of that tab, simulating a slow
+  update that can arrive after the user has already acted.
+
+## Steps
+
+### Baseline
+
+1. Launch the app and navigate to **Stale update rejection**.
+
+- [ ] Expected: The **First** tab is selected. The content area shows
+  `heavyRender: false` and `rejectStaleNavStateUpdates: true`.
+  No toast is visible.
+
+---
+
+### Stale rejection triggered by heavy render
+
+2. Tap the **Third** tab in the native tab bar to navigate to it. Tap
+   **Toggle heavyRender** on the Third tab to enable heavy render.
+
+- [ ] Expected: The label updates to `heavyRender: true`. No toast
+  appears.
+
+3. Tap the **First** tab bar item to go back to the First tab. Tap
+   **Select Third** (JS dispatches a navigation update to Third), then
+   immediately tap the **Second** tab bar item.
+
+- [ ] Expected: The tab bar changes to **Second** immediately. After
+  the heavy render on Third finishes, a toast labeled
+  `onTabSelectionRejected` appears. The final active tab is
+  **Second**, not Third.
+
+---
+
+### Disabling rejectStaleNavStateUpdates at runtime
+
+4. Navigate to the **Third** tab (heavy render still enabled). Tap
+   **Toggle rejectStaleNavStateUpdates** to disable it.
+
+- [ ] Expected: The label updates to `rejectStaleNavStateUpdates:
+  false`. No toast fires from this action.
+
+5. Navigate back to **First**. Tap **Select Third**, then immediately
+   tap **Second** in the tab bar before the heavy render ends.
+
+- [ ] Expected: No `onTabSelectionRejected` toast appears. Tab Second is selected
+  immediately but after the 3 000 ms block, the final active tab is
+  **Third**.
+
+6. Tap **Toggle rejectStaleNavStateUpdates** to re-enable it.
+
+- [ ] Expected: Label updates to `rejectStaleNavStateUpdates: true`.
+
+7. Repeat the actions from step 5.
+
+- [ ] Expected: The tab bar changes to **Second** immediately. After
+  the heavy render on Third finishes, a toast labeled
+  `onTabSelectionRejected` appears. The final active tab is
+  **Second**, not Third.