[ci-scan-net11] iOS Mono device tests repeatedly finish with XHarness TESTS_FAILED

## Summary
The iOS Mono device-test submission repeatedly completes with hidden Helix test failures while the AzDO submission task itself remains green.

## Build Information
- **Pipeline**: maui-pr-devicetests
- **Build**: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1584588
- **Build ID**: 1584588
- **Branch**: net11.0
- **First seen**: 2026-09-03
- **Occurrences**: 10 in last 10 builds

## Affected Legs
- DeviceTestsIOS_Mono / Controls.DeviceTests-General / iOS
- DeviceTestsIOS_Mono / Controls.DeviceTests-Shell / iOS

## Error Message
```text
XHarness exit code: 1 (TESTS_FAILED)
```

## Investigation Context
The frozen submission evidence contains three failed Helix work items across iOS simulator variants. The available console evidence reports failed tests but does not expose stable individual test names, so the affected test identities remain uncertain.

Start with build 1584588 and the maui-pr-devicetests pipeline, focusing on the DeviceTestsIOS_Mono Controls.DeviceTests-General and Controls.DeviceTests-Shell iOS legs. Inspect the frozen submission evidence, failure.log, and the three failed Helix work items to identify stable failing test names. Done means the hidden TESTS_FAILED cause is identified and the affected device-test submission no longer repeatedly fails.

Written by the indexing model from the issue text.