fix: handle Windows file persistence races

[yottahmd]

Summary

• replace Windows status-file compaction with MoveFileEx so readers never observe a removed status file between compact and rename
• make proc heartbeat publication recreate its parent directory if concurrent restart cleanup removes it between directory creation and temp-file creation
• add coverage for status-file replacement and proc heartbeat publication with a missing parent directory

Testing

• go test ./internal/cmn/fileutil -count=1
• go test ./internal/persis/fileproc -count=1
• go test ./internal/cmd -run TestRestartCommand_BuiltExecutableRestoresExplicitEnv -count=5
• go test ./internal/cmd -count=1
• go test ./internal/service/frontend/api/v1 -run 'TestApproveDAGRunStep|TestApproveDAGRunStepWithInputs|TestApproveDAGRunStepMissingRequired' -count=5
• go test ./internal/persis/filedagrun -count=1
• go test ./internal/service/frontend/api/v1 -count=1
• go test ./internal/cmn/fileutil ./internal/persis/fileproc ./internal/persis/filedagrun ./internal/service/frontend/api/v1 -count=1
• env GOOS=windows GOARCH=amd64 go test -c -o /tmp/fileutil.test.exe ./internal/cmn/fileutil
• env GOOS=windows GOARCH=amd64 go test -c -o /tmp/api-v1.test.exe ./internal/service/frontend/api/v1
• env GOOS=windows GOARCH=amd64 go test -c -o /tmp/filedagrun.test.exe ./internal/persis/filedagrun
• env GOOS=windows GOARCH=amd64 go test -c -o /tmp/fileproc.test.exe ./internal/persis/fileproc
• env GOOS=windows GOARCH=amd64 go test -c -o /tmp/cmd.test.exe ./internal/cmd
• git diff --check

[coderabbitai]

📝 Walkthrough

Walkthrough

Introduces platform-specific file replacement implementations for Unix and Windows through build-constrained files. Refactors ReplaceFileWithRetry to delegate to the new replaceFile function instead of inlining platform logic. Adds test coverage for file replacement functionality.

Changes

Cohort / File(s)	Summary
Platform-specific implementations internal/cmn/fileutil/replace_unix.go, internal/cmn/fileutil/replace_windows.go	Added Unix and Windows build-constrained implementations of replaceFile. Unix version uses os.Rename; Windows version converts paths to UTF-16 and calls windows.MoveFileEx with MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH flags.
Retry logic refactoring internal/cmn/fileutil/retry.go	Modified ReplaceFileWithRetry to delegate to replaceFile instead of inlining platform-specific stat, removal, and rename operations. Removed fmt import.
Test coverage internal/cmn/fileutil/retry_test.go	Added TestReplaceFileWithRetry with subtests verifying file overwrite and creation scenarios, asserting filesystem state changes.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: handle Windows file persistence races' accurately describes the main change: refactoring file replacement to use platform-specific implementations (MoveFileEx on Windows, os.Rename on Unix) to prevent race conditions during atomic file operations.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-windows-approval-required-flake

Warning

Review ran into problems

🔥 Problems

Timed out fetching pipeline failures after 30000ms

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