fix: retry the Windows activation move on transient access denials

[BartoszBlizniak]

Summary

install.ps1's atomic activation moves the freshly extracted directory into its final versioned location using [System.IO.Directory]::Move. On GitHub-hosted windows-latest runners, this was observed to intermittently fail with:

Access to the path '...' is denied.

(UnauthorizedAccessException, sometimes IOException)

Directory.Move on Windows fails outright if any handle is open on the source or destination path. Microsoft Defender's real-time scan (or Windows Search indexing) can briefly hold a handle on a directory that was just extracted from a zip, causing the move to fail even though nothing in the install itself is wrong — a rerun always passes.

This adds a small bounded retry (Invoke-WithFilesystemRetry: up to 5 attempts, ~250ms apart, total <1.5s) around every Directory.Move in the activation sequence — staged-to-temp, old-to-backup, temp-to-final, and the rollback restore path — retrying only on UnauthorizedAccessException/IOException and rethrowing unchanged after the final attempt. Download retries already had their own Invoke-WithRetry helper with second-scale linear backoff, which is a poor fit here (too slow, and it retries on any exception), so this is a separate, narrower helper mirroring the same scriptblock-based shape.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Refactoring
• Other (please describe)

Validation

• PowerShell AST parse check (install.ps1): pass.
• Invoke-ScriptAnalyzer -Path install.ps1 -Settings PSGallery -EnableExit: pass, no findings.
• pwsh -Command "Invoke-Pester tests/Install.Tests.ps1" on macOS: 5 passed, 0 failed, 27 skipped (Windows-tagged black-box tests self-skip on non-Windows hosts; the new activation-retry unit tests are not Windows-tagged and ran and passed locally, covering: success after N transient UnauthorizedAccessExceptions, success after a transient IOException, exhausting retries and rethrowing, and not retrying unrelated exception types).
• sh -n install.sh: pass, no changes to install.sh.

Compatibility

None. No change to supported targets, options, environment variables, installation paths, or the four-line output contract. Activation now tolerates transient filesystem access errors instead of surfacing them as install failures; genuine (non-transient) access/IO errors still fail the install after 5 attempts, same as before but slightly slower to surface.

Checklist

• I have added or updated tests where appropriate.
• I have updated documentation and CHANGELOG.md where appropriate.
• I have not included credentials, tokens, or other sensitive data.
• I have called out any breaking change explicitly.

[Copilot]

Pull request overview

Improves the PowerShell installer’s reliability on Windows by tolerating transient filesystem access denials (e.g., Defender/indexer briefly holding handles) during the atomic “activation” directory moves.

Changes:

• added Invoke-WithFilesystemRetry to retry only UnauthorizedAccessException/IOException with a small bounded delay.
• wrapped activation/rollback Directory.Move operations in install.ps1 with the new filesystem retry helper.
• added Pester unit tests for the new retry helper and documented the fix in CHANGELOG.md.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
install.ps1	Adds a targeted filesystem retry helper and applies it around activation/rollback directory moves.
tests/Install.Tests.ps1	Adds unit tests validating retry behavior, exhaustion/rethrow, and non-retry for unrelated exceptions.
CHANGELOG.md	Notes the Windows activation transient access-denied retry behavior under Unreleased fixes.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.