GeezerVison

Backport of #27373 to release/v7.5.12

Triggered by Aditya Patwardhan (@adityapatwardhan) on behalf of Justin Chung (@jshigetomi)

Original CL Label: CL-Engine

/cc @PowerShell/powershell-maintainers

Impact

REQUIRED: Choose either Tooling Impact or Customer Impact (or both). At least one checkbox must be selected.

Tooling Impact

• Required tooling change
• Optional tooling change (include reasoning)

Customer Impact

• Customer reported
• Found internally

Found internally after reports of PowerShell failing at startup when a per-user powershell.config.json is temporarily unreadable or malformed. The expected behavior is to warn and fall back to defaults for the current-user file while retaining strict failure for the system-wide configuration.

Regression

REQUIRED: Check exactly one box.

• Yes
• No

This is not a regression.

Testing

The original PR adds focused xUnit coverage for broken and type-mismatched current-user configuration, fallback defaults, warning emission, and continued system-wide strict failure. The backport cherry-picked cleanly and passes git diff --check, resource XML parsing, and conflict-marker scanning. A targeted dotnet test attempt was blocked during build by pre-existing missing DotNetEventingStrings generated resources in Microsoft.PowerShell.CoreCLR.Eventing, before the selected tests could run.

Risk

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• High
• Medium
• Low

Medium risk because this changes early startup configuration error handling, but only for the per-user scope; the system-wide security-relevant configuration remains fail-closed. The original change includes focused xUnit coverage and cherry-picked cleanly.