Test failure: GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok times out on macOS (runtime-extra-platforms)

## Test failure

`System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok` is failing intermittently on **macOS** (`OSX.15.Amd64.Open`, `OSX.26.Arm64.Open`) in the `runtime-extra-platforms` pipeline.

### Error message

```
System.TimeoutException : The operation has timed out.
```

### Frequency

8 builds on **main** over the past 14 days (plus a few PR runs), exclusively on macOS queues. Ongoing since 2026-08-12.

## Analysis

This is the macOS name-resolution flakiness long tracked by the umbrella issue #1488. The sibling `GetHostEntry*` tests already opt out of macOS via the `GetHostEntryWorks` gate, which is annotated with that issue:

`src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs`

```csharp
public static bool GetHostEntryWorks =
// [ActiveIssue("https://github.com/dotnet/runtime/issues/27622")]
PlatformDetection.IsNotArmNorArm64Process &&
// [ActiveIssue("https://github.com/dotnet/runtime/issues/1488", TestPlatforms.OSX)]
!PlatformDetection.IsOSX &&
...
```

However, `Dns_GetHostEntryAsync_IPAddress_Ok` is **not** covered by that gate — it only requires multithreading:

```csharp
[ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsMultithreadingSupported))]
public async Task Dns_GetHostEntryAsync_IPAddress_Ok()
{
IPAddress localIPAddress = await TestSettings.GetLocalIPAddress();
await TestGetHostEntryAsync(() => Dns.GetHostEntryAsync(localIPAddress));
}
```

So the reverse lookup of the local IP address (`Dns.GetHostEntryAsync(localIPAddress)`) intermittently times out on the macOS CI resolver, exactly the flakiness #1488 describes for the other tests. Filing a dedicated Known Build Error so Build Analysis can auto-match this specific failure (the umbrella #1488 has no known-issue JSON blob).

## Suggested fix

Gate this test on macOS the same way as its siblings — add `!PlatformDetection.IsOSX` (referencing #1488) to the condition, or move it behind the existing `GetHostEntryWorks` check.

## Sample console log

https://helixr1107v0xdeko0k025g8.blob.core.windows.net/dotnet-runtime-refs-heads-main-51264a0b9e1b49bb9f/System.Net.NameResolution.Functional.Tests/2/console.58c2e797.log?helixlogtype=result

## Known issue error message

Fill the error message using [known issues](https://github.com/dotnet/arcade/blob/main/Documentation/Projects/Build%20Analysis/KnownIssues.md).

```json
{
"ErrorPattern": "System\\.Net\\.NameResolution\\.Tests\\.GetHostEntryTest\\.Dns_GetHostEntryAsync_IPAddress_Ok",
"BuildRetry": false,
"ExcludeConsoleLog": false
}
```

### Known issue validation
**Build: :mag_right:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1564198
**Error message validated:** `[System\.Net\.NameResolution\.Tests\.GetHostEntryTest\.Dns_GetHostEntryAsync_IPAddress_Ok`]
**Result validation:** :white_check_mark: Known issue matched with the provided build.
**Validation performed at:** 8/25/2026 2:38:20 PM UTC

### Report

|Build|Repository|Test|Pull Request|
|---|---|---|---|
|[1596321](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1596321)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1596321&view=ms.vss-test-web.build-test-results-tab&runId=44074260&resultId=200420)||
|[1594919](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1594919)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1594919&view=ms.vss-test-web.build-test-results-tab&runId=44033712&resultId=201372)||
|[1594314](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1594314)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1594314&view=ms.vss-test-web.build-test-results-tab&runId=44011148&resultId=182634)||
|[1593920](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1593920)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1593920&view=ms.vss-test-web.build-test-results-tab&runId=43997294&resultId=183981)||
|[1593809](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1593809)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1593809&view=ms.vss-test-web.build-test-results-tab&runId=43994774&resultId=149512)||
|[1593470](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1593470)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1593470&view=ms.vss-test-web.build-test-results-tab&runId=43988074&resultId=182900)||
|[1592299](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1592299)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1592299&view=ms.vss-test-web.build-test-results-tab&runId=43958338&resultId=182656)||
|[1591859](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591859)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591859&view=ms.vss-test-web.build-test-results-tab&runId=43943876&resultId=196804)||
|[1591180](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591180)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591180&view=ms.vss-test-web.build-test-results-tab&runId=43928756&resultId=183729)||
|[1590326](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1590326)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1590326&view=ms.vss-test-web.build-test-results-tab&runId=43896712&resultId=183443)||
|[1590019](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1590019)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1590019&view=ms.vss-test-web.build-test-results-tab&runId=43891736&resultId=160857)||
|[1588952](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1588952)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1588952&view=ms.vss-test-web.build-test-results-tab&runId=43863462&resultId=184246)||
|[1585519](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1585519)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1585519&view=ms.vss-test-web.build-test-results-tab&runId=43754874&resultId=203124)||
|[1584749](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1584749)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1584749&view=ms.vss-test-web.build-test-results-tab&runId=43727174&resultId=187773)||
|[1583662](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1583662)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1583662&view=ms.vss-test-web.build-test-results-tab&runId=43696738&resultId=201092)||
|[1580168](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1580168)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1580168&view=ms.vss-test-web.build-test-results-tab&runId=43596254&resultId=200229)||
|[1580178](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1580178)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1580178&view=ms.vss-test-web.build-test-results-tab&runId=43591888&resultId=203430)||
|[1580124](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1580124)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1580124&view=ms.vss-test-web.build-test-results-tab&runId=43588358&resultId=182977)||
|[1576120](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1576120)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1576120&view=ms.vss-test-web.build-test-results-tab&runId=43449674&resultId=182634)|dotnet/runtime#132997|
|[1575978](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1575978)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1575978&view=ms.vss-test-web.build-test-results-tab&runId=43442622&resultId=201187)||
|[1575596](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1575596)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1575596&view=ms.vss-test-web.build-test-results-tab&runId=43433506&resultId=201708)||
|[1574779](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1574779)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1574779&view=ms.vss-test-web.build-test-results-tab&runId=43406576&resultId=182808)|dotnet/runtime#132740|
|[1573739](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1573739)|dotnet/runtime|[System.Net.NameResolution.Functional.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1573739&view=ms.vss-test-web.build-test-results-tab&runId=43361676&resultId=219452)||
|[1573274](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1573274)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1573274&view=ms.vss-test-web.build-test-results-tab&runId=43343806&resultId=183614)||
|[1572675](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1572675)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1572675&view=ms.vss-test-web.build-test-results-tab&runId=43328828&resultId=200268)||
|[1572439](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1572439)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1572439&view=ms.vss-test-web.build-test-results-tab&runId=43319600&resultId=201140)|dotnet/runtime#132887|
|[1569865](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1569865)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1569865&view=ms.vss-test-web.build-test-results-tab&runId=43230202&resultId=143807)||
|[1569716](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1569716)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1569716&view=ms.vss-test-web.build-test-results-tab&runId=43226788&resultId=168128)||
|[1567845](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1567845)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1567845&view=ms.vss-test-web.build-test-results-tab&runId=43175878&resultId=183503)||
|[1567122](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1567122)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1567122&view=ms.vss-test-web.build-test-results-tab&runId=43163816&resultId=175293)||
|[1564198](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1564198)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1564198&view=ms.vss-test-web.build-test-results-tab&runId=43071704&resultId=144588)||
|[1563837](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1563837)|dotnet/runtime|[System.Net.NameResolution.Tests.GetHostEntryTest.Dns_GetHostEntryAsync_IPAddress_Ok](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1563837&view=ms.vss-test-web.build-test-results-tab&runId=43058602&resultId=143618)||
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|1|12|32|

Start in src/libraries/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs and compare Dns_GetHostEntryAsync_IPAddress_Ok with the sibling tests using GetHostEntryWorks. Verify the macOS condition and the #1488 reference, then run the relevant NameResolution functional tests. Done means the test is excluded on macOS and the known-issue validation still matches the reported failure.

Written by the indexing model from the issue text.