[CI] Flaky: HarnessException "Unable to evaluate the property OutputPath" (exit code 139)

## Flaky Test Report (automated)

**Test:** xharness `AppBundleLocator.GetPropertyByMSBuildEvaluationAsync` — MSBuild property evaluation crashes
**Platform:** macOS, Mac Catalyst
**Category:** Flaky / Infrastructure
**Period:** June 22–29, 2026

### Occurrence Summary

| PR | Build | Configuration | Bot | Direct Link |
|--------|----------|-------------------------------------------------------------------------------|---------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| #25713 | 14515144 | link all/macOS/Debug (PrepareAssemblies, CoreCLR, Trimmable Static Registrar) | AcesShared 9 | [Run tests](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=14515144&view=logs&j=1df6e9c4-19a8-54e7-464f-11abfb1bddb9&t=8e629c7c-9bea-5ac6-e9eb-6fb5e474f560) |
| #25849 | 14515024 | trimmode link/Mac Catalyst/Release | AcesShared 81 | [Run tests](https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=14515024&view=logs&j=dc49fd7f-b39a-580f-b9a6-2209b7abaf55&t=1df1eb8b-f9c9-5620-65f1-63d8d5893e86) |

**Total:** Failed in 2 builds across 2 unrelated PRs.

### Error Details

Both failures share the same pattern — the MSBuild property evaluation subprocess **crashes with exit code 139** (SIGSEGV — segmentation fault). This prevents xharness from locating the app bundle and the entire test configuration fails:

**Build 14515144 (PR#25713):**
```
HarnessException: Unable to evaluate the property OutputPath in
/Users/cloudtest/vss/_work/1/s/macios/tests/xharness/bin/Debug/tmp-test-dir/link all474/link all.csproj,
build failed with exit code 139. Timed out: False
at Xharness.AppBundleLocator.GetPropertyByMSBuildEvaluationAsync(...)
at Xharness.AppBundleLocator.LocateAppBundle(...)
at Xharness.Jenkins.TestTasks.MacExecuteTask.RunTestAsync()
```

**Build 14515024 (PR#25849):**
```
HarnessException: Unable to evaluate the property OutputPath in
/Users/cloudtest/vss/_work/1/s/macios/tests/xharness/bin/Debug/tmp-test-dir/trimmode link94/trimmode link.csproj,
build failed with exit code 139. Timed out: False
at Xharness.AppBundleLocator.GetPropertyByMSBuildEvaluationAsync(...)
at Xharness.AppBundleLocator.LocateAppBundle(...)
at Xharness.Jenkins.TestTasks.MacExecuteTask.RunTestAsync()
```

### Analysis

- **Exit code 139 = SIGSEGV** — the dotnet process that evaluates MSBuild properties is crashing with a segmentation fault.
- Both occurrences are on **AcesShared** pool bots (9 and 81), suggesting this may be related to the bot environment (e.g., corrupted dotnet install, missing shared libraries, or memory issues on these VMs).
- The failures are in different test suites (`link all` on macOS and `trimmode link` on MacCatalyst) but both hit the same code path (`AppBundleLocator.GetPropertyByMSBuildEvaluationAsync`).
- This is likely a transient infrastructure issue on AcesShared bots rather than a code bug.

### Classification

This failure was identified as **flaky/infrastructure** because:
- It appeared across 2 unrelated PRs (#25713, #25849)
- The crash (SIGSEGV) in a dotnet subprocess is not caused by test code
- Both occurrences are on AcesShared pool bots

---
*This issue was automatically generated by CI post-mortem analysis.*

Start with xharness's AppBundleLocator.GetPropertyByMSBuildEvaluationAsync call path and the MacExecuteTask.RunTestAsync failures described in the logs. Reproduce the link all/macOS/Debug and trimmode link/Mac Catalyst/Release configurations on the AcesShared environment, then verify that MSBuild property evaluation completes without exit code 139 and the affected tests pass.

Written by the indexing model from the issue text.