Kusto emulator tests fail on Linux CI because kustainer-linux requires SSE4.2/AVX2

[sebastienros]

Problem

The Kusto emulator-backed tests in tests/Aspire.Hosting.Azure.Kusto.Tests/KustoFunctionalTests.cs are currently failing on Linux CI.

The emulator container image currently used by Aspire is mcr.microsoft.com/azuredataexplorer/kustainer-linux:latest. That image now exits at startup with an unsupported instruction set error indicating that the Kusto engine requires SSE4.2/AVX2.

Observed failure

• The container starts, becomes briefly reachable, then exits
• The health check fails with The response ended prematurely
• The container log shows: E_UNSUPPORTED_INSTRUCTION_SET: The Kusto engine can only run on processors that support SSE4.2/AVX2

Affected tests

• KustoEmulator_Starts
• KustoEmulator_WithDatabase_CanReadIngestedData
• KustoEmulator_WithDatabaseThatAlreadyExists_ErrorIsIgnored
• KustoEmulator_WithInvalidDatabase_LogsErrorAndContinues
• KustoEmulator_WithBindMount_IsUsedForPersistence

Notes

This looks like external image drift rather than a repo-side logic regression, since the tests depend on :latest. We should either pin the emulator to a known-good image or digest, or update the test strategy for Linux CI.