[ci-scan] Hang: System.Net.Http.Functional.Tests.HttpClientHandlerTest_BasicAuth.RefreshesPreAuthCredentialsOnChange

## Build Information
Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1577981
Build error leg or test failing: linux-x64 Debug CoreCLR_AllSubsets-System.Net.Http.Functional.Tests
Pull request: https://github.com/dotnet/runtime/pull/133060

KBE authoring guidance (ci-failure-scan)

- `Error Details` is for readers. Paste the full exception, stack trace, or build error excerpt so the failure is understandable without opening the raw log.
- Build Analysis parses only the single JSON block under `Error Message`.
- `ErrorMessage` is a case-sensitive ordinal `String.Contains` substring copied verbatim from the failing log.
- Set `BuildRetry` to `true` only for a clear infrastructure retry case. `ExcludeConsoleLog` disables Helix console-log scanning.

## Error Details

```
System.Net.Http.Functional.Tests.HttpClientHandlerTest_BasicAuth.RefreshesPreAuthCredentialsOnChange [FAIL]
System.TimeoutException : The operation has timed out.
Stack Trace:
/_/src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.BasicAuth.cs(75,0): at System.Net.Http.Functional.Tests.HttpClientHandlerTest_BasicAuth.RefreshesPreAuthCredentialsOnChange()
--- End of stack trace from previous location ---
```

Affected queue: `ubuntu.2604.amd64.open.rt`

Helix job: https://helix.dot.net/api/jobs/1fff4b0c-0613-4830-a8cf-176822b9f5ad/details

Console log: https://helix.dot.net/api/2019-06-17/jobs/1fff4b0c-0613-4830-a8cf-176822b9f5ad/workitems/System.Net.Http.Functional.Tests/console

The test assembly reported 5,466 tests, with this as its only failure.

## Error Message

```json
{
"ErrorMessage": [
"System.Net.Http.Functional.Tests.HttpClientHandlerTest_BasicAuth.RefreshesPreAuthCredentialsOnChange [FAIL]",
"System.TimeoutException : The operation has timed out."
],
"ErrorPattern": "",
"BuildRetry": false,
"ExcludeConsoleLog": false
}
```

Agentic workflow metadata (ci-failure-scan)

Workflow artifact: ci-failure-scan
Artifact kind: kbe-verification
Verified match count: 1 hits in failure.log

> [!NOTE]
> This issue draft was prepared with GitHub Copilot assistance and reviewed by the submitting developer.

### Known issue validation
**Build: :mag_right:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1577981
**Error message validated:** `[System.Net.Http.Functional.Tests.HttpClientHandlerTest_BasicAuth.RefreshesPreAuthCredentialsOnChange [FAIL] System.TimeoutException : The operation has timed out.`]
**Result validation:** :white_check_mark: Known issue matched with the provided build.
**Validation performed at:** 9/2/2026 3:53:38 PM UTC

### Report

|Build|Repository|Test|Pull Request|
|---|---|---|---|
|[1594338](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1594338)|dotnet/runtime|[System.Net.Http.Functional.Tests.HttpClientHandlerTest_BasicAuth.RefreshesPreAuthCredentialsOnChange](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1594338&view=ms.vss-test-web.build-test-results-tab&runId=44011098&resultId=219853)|dotnet/runtime#133606|
|[1590759](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1590759)|dotnet/runtime|[System.Net.Http.Functional.Tests.HttpClientHandlerTest_BasicAuth.RefreshesPreAuthCredentialsOnChange](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1590759&view=ms.vss-test-web.build-test-results-tab&runId=43911388&resultId=215310)|dotnet/runtime#131794|
|[1582740](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1582740)|dotnet/runtime|[System.Net.Http.Functional.Tests.HttpClientHandlerTest_BasicAuth.RefreshesPreAuthCredentialsOnChange](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1582740&view=ms.vss-test-web.build-test-results-tab&runId=43664788&resultId=214901)|dotnet/runtime#133174|
|[1579098](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1579098)|dotnet/runtime|[System.Net.Http.Functional.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1579098&view=ms.vss-test-web.build-test-results-tab&runId=43549206&resultId=219767)||
|[1577981](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1577981)|dotnet/runtime|[System.Net.Http.Functional.Tests.HttpClientHandlerTest_BasicAuth.RefreshesPreAuthCredentialsOnChange](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1577981&view=ms.vss-test-web.build-test-results-tab&runId=43510208&resultId=214990)|dotnet/runtime#133060|
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|0|2|5|

Start with src/libraries/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.BasicAuth.cs at line 75 and review the RefreshesPreAuthCredentialsOnChange test. Re-run that test in the linux-x64 Debug CoreCLR_AllSubsets-System.Net.Http.Functional.Tests leg and inspect the linked Helix console log for the timeout. Done means the test completes reliably without timing out.

Written by the indexing model from the issue text.