[ci-scan] Hang: System.Diagnostics.Process.Tests times out on windows-x64

## Build Information
Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1526411
Build error leg or test failing: windows-x64 Release NativeAOT_Libs-System.Diagnostics.Process.Tests
Reproduced in follow-up build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1526686

## Error Details

The entire `System.Diagnostics.Process.Tests` work item hangs on the `windows-x64 Release NativeAOT_Libs` leg of `runtime-nativeaot-outerloop`. The assembly starts, runs its `[SKIP]` set, then the process never completes and the Helix executor kills it at the 900s timeout. No `[FAIL]` line is emitted — the work item exits via executor timeout (exit code -3).

```
Running assembly:System.Diagnostics.Process.Tests, Version=11.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51
[SKIP] System.Diagnostics.Tests.ProcessCollectionTests.TestThreadCollectionBehavior
...
[EXECUTION TIMED OUT]
Exit Code:-3Executor timed out after 900 seconds and was killed
['System.Diagnostics.Process.Tests' END OF WORK ITEM LOG: Command timed out, and was killed]
```

## Error Message

```json
{
"ErrorMessage": ["Running assembly:System.Diagnostics.Process.Tests", "Executor timed out after 900 seconds and was killed"],
"ErrorPattern": "",
"BuildRetry": false,
"ExcludeConsoleLog": false
}
```

---
Filed by [`ci-failure-scan`](https://github.com/dotnet/runtime/blob/main/.github/workflows/ci-failure-scan.md) (detection only). [`ci-failure-fix`](https://github.com/dotnet/runtime/blob/main/.github/workflows/ci-failure-fix.md) walks open `[ci-scan]` KBEs and either opens a small fix PR or comments here to loop in owners — it never disables the test.

> [!NOTE]
> This issue was generated by an AI agent (GitHub Copilot / `ci-failure-scan`).

> [!WARNING]
>
> Firewall blocked 1 domain
>
> The following domain was blocked by the firewall during workflow execution:
>
> - `awmgmcpg`
>> To allow these domains, add them to the `network.allowed` list in your workflow frontmatter:
>
> ```yaml
> network:
> allowed:
> - defaults
> - "awmgmcpg"
> ```
>
> See [Network Configuration](https://github.github.com/gh-aw/reference/network/) for more information.
>
>

> Generated by [CI Outer-Loop Failure Scanner](https://github.com/dotnet/runtime/actions/runs/30202824402) · 748.4 AIC · ⌖ 17.5 AIC · ⊞ 18.6K · [◷](https://github.com/search?q=repo%3Adotnet%2Fruntime+is%3Aissue+%22gh-aw-workflow-call-id%3A+dotnet%2Fruntime%2Fci-failure-scan%22&type=issues)

### Report

|Build|Repository|Test|Pull Request|
|---|---|---|---|
|[1560942](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1560942)|dotnet/runtime|[System.Diagnostics.Process.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1560942&view=ms.vss-test-web.build-test-results-tab&runId=42978054&resultId=180596)||
|[1559985](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1559985)|dotnet/runtime|[System.Diagnostics.Process.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1559985&view=ms.vss-test-web.build-test-results-tab&runId=42946170&resultId=183188)||
|[1559436](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1559436)|dotnet/runtime|[System.Diagnostics.Process.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1559436&view=ms.vss-test-web.build-test-results-tab&runId=42930880&resultId=182716)||
|[1558955](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1558955)|dotnet/runtime|[System.Diagnostics.Process.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1558955&view=ms.vss-test-web.build-test-results-tab&runId=42917162&resultId=179882)||
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|0|0|4|

### Known issue validation
**Build: :mag_right:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1526411
**Error message validated:** `[Running assembly:System.Diagnostics.Process.Tests Executor timed out after 900 seconds and was killed`]
**Result validation:** :white_check_mark: Known issue matched with the provided build.
**Validation performed at:** 7/28/2026 7:48:05 AM UTC

Start with the linked build logs for the windows-x64 Release NativeAOT_Libs-System.Diagnostics.Process.Tests work item and compare the reproduced and later reported runs. Investigate where System.Diagnostics.Process.Tests stops after its skipped tests; done means the work item completes on that leg without the 900-second executor timeout.

Written by the indexing model from the issue text.