Fix MAUI Android inner loop MSBuild arg splitting on Helix

[LoopedBard3]

Problem

An inner loop MAUI Android device run showed MSBuild /p: arguments being executed as standalone shell commands:

(.venv) D:\...>/p:PublishReadyToRun=false
The filename, directory name, or volume label syntax is incorrect.

(.venv) D:\...>/p:PublishReadyToRunComposite=false /p:RuntimeIdentifier=android-arm64 /p:SupportedOSPlatformVersion=24 /p:TargetFrameworks=net11.0-android"
The filename, directory name, or volume label syntax is incorrect.

setup_helix.py's restore also silently received only the first arg (/p:UseMonoRuntime=false), dropping the R2R args.

Root cause

In eng/performance/maui_scenarios_android_innerloop.proj, the coreclr branch built _MSBuildArgs joining args with ;:

$(_MSBuildArgs);/p:PublishReadyToRun=false;/p:PublishReadyToRunComposite=false

_MSBuildArgs is passed to Helix as a single quoted argument (--msbuild-args "$(_MSBuildArgs)" and setup_helix.py ... "$(_MSBuildArgs)"). Helix treats ; as a command separator when generating the run script — the same behavior the set X=Y;set A=B env-var blocks rely on. So the semicolons split the quoted argument across separate command lines: the first piece kept the opening quote, and the remaining /p: pieces ran as their own commands.

Mono builds were unaffected because that path never introduced a ;.

Fix

Use spaces instead of ;, consistent with every other append in that PropertyGroup. The Python side (re.split(r'[;\s]+', ...) in both runner.py and setup_helix.py) already splits on whitespace, so args still parse correctly into the subprocess.run argument list — and now every arg actually reaches Python and MSBuild.

[Copilot]

Pull request overview

This pull request fixes MAUI Android inner-loop Helix runs where MSBuild /p: arguments were being split into separate shell commands, causing later arguments to be dropped or executed incorrectly.

Changes:

• Update the CoreCLR _MSBuildArgs append logic to use spaces instead of semicolons when adding ReadyToRun-related /p: arguments.
• Expand the inline comment to document why ; is unsafe for _MSBuildArgs when passed through Helix as a single quoted argument.

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