How can a reproducible Windows Shell32 environment-regeneration defect be escalated to Windows engineering?

I have investigated a reproducible Windows 11 environment-regeneration defect and would like to know the appropriate way to escalate the findings to the Windows Shell engineering team.

Problem summary

When the expected combined Machine PATH and User PATH reaches 4095 characters, Windows Shell32's environment-regeneration logic silently omits the entire User PATH, leaving only the Machine PATH.

In controlled tests, the internal, undocumented shell32.dll!RegenerateUserEnvironment function returned TRUE despite producing an incomplete PATH.

This can cause user-installed command-line tools to become inaccessible through normal command lookup, even though their executables and User PATH registry entries remain intact.

Verified environments

Windows 11 24H2 (OS Build 26100.4770)

• shell32.dll version: 10.0.26100.4768
• Relatively clean VM without ExplorerPatcher
• Standard, non-elevated PowerShell 5.1 process
• Expected combined PATH length 4094: correct
• Expected combined PATH length 4095: User PATH completely omitted
• CreateEnvironmentBlock successfully constructs the complete PATH using the same registry values

Windows 11 26H2 (OS Build 26300.9818)

• shell32.dll version: 10.0.26100.9949
• Exact 4094/4095 boundary independently reproduced on one additional PC
• A separate PC reproduced Machine-only PATH regeneration with an existing combined Process PATH of 4162 characters

Root-cause investigation

Using WinDbg on the 24H2 VM, I traced the failure to a length check within:

shell32!BuildEnvironmentPath

The relevant conditional branch skips the User PATH append operation at the failing boundary.

A controlled in-memory diagnostic experiment on the disposable VM provided strong evidence that this check is responsible for the observed behavior. No production system DLL was modified.

This appears to be an issue in Windows Shell32 rather than WinGet, PowerShell, or a third-party shell modification.

Existing reports

I have already submitted the findings through Windows Feedback Hub and privately to Microsoft Security Response Center for assessment of potential security implications.

I also published the reproducible test results, screenshots, and original VM test transcript in this related GitHub discussion:

https://github.com/microsoft/winget-cli/issues/6606#issuecomment-6702696239

My question

What is the appropriate Microsoft-supported process for having a reproducible Windows Shell32 implementation defect, with WinDbg root-cause evidence, reviewed by the Windows product engineering team?

Since the issue has already been reported through Feedback Hub and MSRC, I would especially appreciate guidance on whether there is a way to associate the existing reports with the Windows Shell engineering team or obtain an engineering-level investigation without opening a paid Windows SDK support incident.

I understand that RegenerateUserEnvironment is undocumented, but the observable impact concerns the effective environment received by Windows applications and command-line tools.

Thank you for any guidance on routing this issue to the appropriate product team.