[Bug] RuntimeBroker crashes with NullReferenceException when macOS SSO extension is inactive

[TomProkop]

Summary

In this repro environment, the macOS broker path ends in NullReferenceException after broker startup fails.

Environment

• Microsoft.Identity.Client.Broker 4.83.3
• Microsoft.Identity.Client.NativeInterop 0.20.3
• .NET 10.0.105
• macOS 26.3.1, arm64

Repro

Observed through an app using the macOS broker path (WithBroker(new BrokerOptions(OperatingSystems.OSX))) and also confirmed by calling the native runtime directly.

Direct native call result:

• MSALRUNTIME_Startup() returns ApiContractViolation (status 6)
• context: SSO extension is inactive or is not available on this device.

Decompiled RuntimeBroker behavior:

• RuntimeBroker catches MsalRuntimeException with ResponseStatus.ApiContractViolation
• stores it in s_initException
• returns null from the Lazy<Core> factory
• later uses of s_lazyCore.Value are not null-checked and end in NullReferenceException

Expected behavior

If broker startup is unavailable, MSAL should surface a descriptive exception or broker-unavailable result. It should not degrade into NullReferenceException.

Notes

This issue is intentionally scoped to the environment above. Related consumer repro: microsoft/powerplatform-build-tools#1352

[github-actions]

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