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This section details on the original issue you should resolve

<issue_title>OmniSharp tests have been failing silently</issue_title>
<issue_description>OmniSharp tests show the following output:

Executing: /__w/1/s/artifacts/obj/extracted-dotnet-sdk/dotnet new <template> --name OmniSharpTests_<template> --output /__w/1/s/artifacts/bin/Microsoft.DotNet.SourceBuild.Tests/Release/projects-202512151127508377/OmniSharpTests_<template>
Executing: /__w/1/s/artifacts/bin/Microsoft.DotNet.SourceBuild.Tests/Release/OmniSharpTests/run -s /__w/1/s/artifacts/bin/Microsoft.DotNet.SourceBuild.Tests/Release/projects-202512151127508377/OmniSharpTests_<template>
/__w/1/s/artifacts/bin/Microsoft.DotNet.SourceBuild.Tests/Release/OmniSharpTests/run: line 19: mono: command not found

The underlying OmniSharp runner script fails to execute, but the test suite still reports the result as a success instead of a failure or skip.</issue_description>

<agent_instructions>Two things that need to be done:

• Update the test so that it produce a failure instead of silently passing
• Figure out why this is failing in the main branch but not the release/10.0.1xx branch.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@mthalman This behavior is only occurring in main branch.