fix(deps): update module golang.org/x/sys to v0.39.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
golang.org/x/sys	v0.38.0 -> v0.39.0

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Enabled.

♻ Rebasing: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

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[claude]

Code Review: Dependency Update - golang.org/x/sys v0.38.0 → v0.39.0

Summary

This PR updates the golang.org/x/sys dependency from v0.38.0 to v0.39.0. This is a minor version bump in the supplementary Go system call package.

✅ Code Quality & Best Practices

• Clean dependency update: The change follows proper Go module versioning
• Automated process: Renovate bot ensures consistent dependency management
• Minimal scope: Only touches go.mod and go.sum files as expected

🔍 Impact Analysis

The golang.org/x/sys package is used in this codebase for:

• Unix systems (control_unix.go:10): Socket options (SO_REUSEADDR, SO_REUSEPORT)
• Windows systems (control_windows.go:6): Socket options (SO_REUSEADDR)

These are low-level system calls for socket reuse, critical for the FTP server's active/passive transfer modes.

🔒 Security Considerations

Low Risk - This is a standard maintenance update to a well-maintained Go supplementary package. The golang.org/x/sys package typically includes:

• Bug fixes for system call handling
• Support for newer OS versions
• Performance improvements

No known security vulnerabilities were introduced or fixed in this specific version bump.

🧪 Test Coverage Recommendation

Given the usage in socket control operations, I recommend:

1. Run the full test suite with race detection (as per CLAUDE.md):

   go test -parallel 20 -v -race -coverprofile=coverage.txt -covermode=atomic ./...

2. Focus on transfer tests: The socket reuse functionality is critical for:
   • Active transfer mode (transfer_active_test.go)
   • Passive transfer mode (tested in transfer_test.go)
   • Concurrent client connections (client_handler_test.go)

⚡ Performance Considerations

Neutral to Positive - System library updates typically include optimizations. No performance regressions expected.

🎯 Recommendation

APPROVE ✓

This is a routine maintenance update with:

• Low risk profile
• Standard dependency management
• Proper version constraints maintained
• Automerge enabled appropriately for this type of change

The PR aligns with the project's automated dependency management strategy and should proceed once CI passes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.88%. Comparing base (e349ca9) to head (88be58e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #591   +/-   ##
=======================================
  Coverage   86.88%   86.88%           
=======================================
  Files          12       12           
  Lines        1761     1761           
=======================================
  Hits         1530     1530           
  Misses        155      155           
  Partials       76       76           

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