PR Summary

This pull request improves how PowerShell handles unreadable or malformed per-user configuration files. Instead of failing to start, PowerShell now falls back to default settings and emits a warning when the per-user config is unreadable, while maintaining strict failure for system-wide config issues. This addresses a startup-time crash caused by transient cloud file provider failures (e.g., OneDrive not yet running on a fresh login). The PR also adds new tests to verify this behavior.

Configuration file handling improvements:

• Updated PSConfiguration.cs so the per-user (ConfigScope.CurrentUser) config read fails open in two places:
  • File-level fallback: opening or root-parsing the file. Catches IOException, UnauthorizedAccessException, SecurityException, and JsonException (including the OneDrive-cloud-file-provider IOException that motivated PS7 should revert to defaults if it can't load user powershell.config.json #27370).
  • Per-key fallback: when a syntactically valid file contains a value that can't be materialized as the target type (e.g., PowerShellPolicies.ScriptExecution is a string instead of an object). Catches JsonException / JsonSerializationException from jToken.ToObject<T>(serializer) so a single malformed setting doesn't crash startup.
• Both fallback paths route through a single TryWriteConfigWarning helper that writes a best-effort warning to Console.Error. Console.Error is intentional at this layer: ReadValueFromFile runs very early in startup, before any host, runspace, or PowerShell warning stream exists. This matches existing startup-time stderr writes in ConsoleHost.cs (e.g., CannotLoadPSReadline, SlowProfileLoadingMessage). Centralizing the call gives future hosts a single seam to swap the channel.
• Neither fallback applies to the system-wide (ConfigScope.AllUsers) config file, which remains a hard failure for security reasons (admin-owned, sole source of security-relevant policies on non-Windows).
• Added two new localized resource strings to PSConfigurationStrings.resx:
  • CanNotReadConfigurationFile — for the file-level fallback.
  • CanNotReadConfigurationValue — for the per-key fallback.
  • Strings are prefix-free; the helper applies the WARNING: label so the resource content stays usable if a future host routes these through the warning stream.

Testing enhancements:

• Added two fixture helpers in test_PSConfiguration.cs:
  • SetupBrokenCurrentUserConfigOnly — broken per-user config, no system config (file-level path).
  • SetupTypeMismatchedCurrentUserConfig — valid JSON with a wrong nested shape (per-key path).
• Added a CaptureStderr(Action) helper that redirects Console.Error so tests can assert the warning was actually emitted.
• New / updated xUnit tests:
  • PowerShellConfig_BrokenSystemConfig_Throws_BrokenCurrentUserConfig_FallsBack (renamed from PowerShellConfig_GetPowerShellPolicies_BrokenSystemConfig) — asserts both fail-closed for AllUsers and fail-open for CurrentUser.
  • PowerShellConfig_BrokenCurrentUserConfig_FallsBackToDefaults — broken per-user file returns defaults via GetExecutionPolicy, GetModulePath, GetExperimentalFeatures.
  • PowerShellConfig_TypeMismatchInCurrentUserConfig_FallsBackToDefaults — valid JSON with a type-mismatched value returns null instead of throwing.
  • PowerShellConfig_BrokenCurrentUserConfig_EmitsWarningToStderr — pins that the file-level warning is actually written.
  • PowerShellConfig_TypeMismatchInCurrentUserConfig_EmitsWarningToStderr — pins that the per-key warning is actually written.

PR Context

Fixes #27370

The original report showed pwsh hard-failing at startup with IOException: The cloud file provider is not running when the user's powershell.config.json lives in a OneDrive-synced Documents\PowerShell folder and OneDrive hasn't started yet. The same code path also blew up on permission-denied and corrupt-JSON cases. After this PR, all of those scenarios warn to stderr and fall back to default settings (so $profile, execution policy, module path, etc. work as if the file were absent), while the admin-owned AllUsers config still fails closed.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge. If this PR is a work in progress, please open this as a Draft Pull Request and mark it as Ready to Review when it is ready to merge.
• Breaking changes
  • None
  • OR
  • Experimental feature(s) needed
    • Experimental feature name(s):
• User-facing changes
  • Not Applicable
  • OR
  • Documentation needed
    • Issue filed:
• Testing - New and feature
  • N/A or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed