[macOS 26] dotnet dev-certs fails to save HTTPS developer certificate in Helix

### Description

WASM Helix work items on `osx.26.arm64.open` intermittently fail during environment setup when `dotnet dev-certs https` cannot save the HTTPS developer certificate. The failure occurs before tests execute and has been observed on multiple machines and builds.

### Reproduction Steps

Run a browser-wasm library test work item on the `osx.26.arm64.open` Helix queue. The failure is intermittent and has been confirmed in builds 1586491 and 1584957.

### Expected behavior

`dotnet dev-certs https` completes successfully and the WASM test executes.

### Actual behavior

```text
+ dotnet dev-certs https
There was an error saving the HTTPS developer certificate to the current user personal certificate store.
+ export _commandExitCode=2
```

The subsequent missing `xharness-event-processor.py` message is secondary to the setup command exiting with code 2.

### Regression?

Unknown.

### Known Workarounds

Retrying is effective. In build 1584957, the affected work item passed after Helix resubmission.

### Configuration

- Queue: `osx.26.arm64.open`
- Architecture: ARM64
- Confirmed on `dci-mac-build-462` running macOS 26.4 and `dci-mac-build-480` running macOS 26.4.1
- SDK: `11.0.100-rc.1.26420.103`

### Other information

This replaces dotnet/dnceng#6723 because the `Known Build Error` label and Build Analysis automation were unavailable there.

## Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586491
Leg Name: `browser-wasm osx Release LibraryTests_SmokeMac - osx.26.arm64.open`

Also observed in https://dev.azure.com/dnceng-public/public/_build/results?buildId=1584957 on a different machine, where the affected work item passed after Helix resubmission.

## Error Details

```text
+ dotnet dev-certs https
There was an error saving the HTTPS developer certificate to the current user personal certificate store.
+ export _commandExitCode=2
```

## Error Message

```json
{
"ErrorMessage": "There was an error saving the HTTPS developer certificate to the current user personal certificate store.",
"BuildRetry": true,
"ExcludeConsoleLog": false
}
```

> [!NOTE]
> This issue was drafted and filed with GitHub Copilot.

### Known issue validation
**Build: :mag_right:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586491
**Error message validated:** `[There was an error saving the HTTPS developer certificate to the current user personal certificate store.`]
**Result validation:** :x: Known issue did not match with the provided build.
**Validation performed at:** 9/8/2026 7:25:27 PM UTC

### Report

|Build|Repository|Test|Pull Request|
|---|---|---|---|
|[1596425](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1596425)|dotnet/runtime|[WasmTestOnChrome-MONO-ST-System.Runtime.InteropServices.JavaScript.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1596425&view=ms.vss-test-web.build-test-results-tab&runId=44072086&resultId=100000)||
|[1594788](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1594788)|dotnet/runtime|[WasmTestOnChrome-MONO-ST-System.Runtime.Intrinsics.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1594788&view=ms.vss-test-web.build-test-results-tab&runId=44026998&resultId=100000)||
|[1593453](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1593453)|dotnet/runtime|[WasmTestOnChrome-MONO-ST-System.Runtime.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1593453&view=ms.vss-test-web.build-test-results-tab&runId=43984056&resultId=100000)||
|[1591427](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591427)|dotnet/runtime|[WasmTestOnChrome-MONO-ST-System.Runtime.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591427&view=ms.vss-test-web.build-test-results-tab&runId=43931488&resultId=100000)|dotnet/runtime#130050|
|[1590497](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1590497)|dotnet/runtime|[WasmTestOnChrome-MONO-ST-System.Runtime.Intrinsics.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1590497&view=ms.vss-test-web.build-test-results-tab&runId=43903616&resultId=100003)||
|[1589719](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1589719)|dotnet/runtime|[WasmTestOnChrome-MONO-ST-System.Runtime.Intrinsics.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1589719&view=ms.vss-test-web.build-test-results-tab&runId=43881166&resultId=100186)||
|[1586600](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586600)|dotnet/runtime|[WasmTestOnChrome-ST-System.Runtime.Extensions.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586600&view=ms.vss-test-web.build-test-results-tab&runId=43783664&resultId=185384)|dotnet/runtime#133391|
|[1586573](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586573)|dotnet/runtime|[WasmTestOnFirefox-ST-System.Net.WebSockets.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586573&view=ms.vss-test-web.build-test-results-tab&runId=43782928&resultId=196495)|dotnet/runtime#133388|
|[1586559](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586559)|dotnet/runtime|[WasmTestOnV8-ST-System.Linq.Queryable.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586559&view=ms.vss-test-web.build-test-results-tab&runId=43782084&resultId=175295)|dotnet/runtime#133387|
|[1586540](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586540)|dotnet/runtime|[normal-System.Formats.Asn1.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1586540&view=ms.vss-test-web.build-test-results-tab&runId=43781240&resultId=170974)|dotnet/runtime#133386|
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|1|6|10|

Start with the failed `dotnet dev-certs https` command and the linked Helix build logs for the `osx.26.arm64.open` queue, comparing the affected macOS 26 machines and successful retries. Done means the HTTPS developer certificate is saved reliably during environment setup and the WASM work item proceeds without requiring resubmission.

Written by the indexing model from the issue text.