[macOS 26] dotnet dev-certs fails to save HTTPS developer certificate in Helix #133435

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

+ 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

+ 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

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

Known issue validation

Build: 🔎 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: ❌ Known issue did not match with the provided build.
Validation performed at: 9/8/2026 7:25:27 PM UTC

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Summary