fix: set close-on-exec on log file descriptors

[drifting-shard]

What changed

Set O_CLOEXEC when opening and creating log files in the default
Unix backend.

Without this flag, applications embedding Raft Engine can leak log file
descriptors into spawned child processes. Those children may keep purged
files alive after unlinking, preventing disk space from being reclaimed.

The flag is applied at open time to avoid the fork/exec race in
multithreaded applications.

Fixes #404

Tests

• cargo fmt --check
• cargo check --lib

The full test suite was not run locally because the bundled grpcio-sys
dependency fails to build on ARM macOS. GitHub Actions runs it on Ubuntu.

Summary by CodeRabbit

• Bug Fixes
  • Improved file descriptor handling to ensure log files are automatically closed when executing other programs.
  • Applied consistent close-on-exec behavior when opening and creating log files.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 3beb504c-6821-4eff-a340-d929945c76e8

📥 Commits

Reviewing files that changed from the base of the PR and between 3258ed1 and 6fa7ac6.

📒 Files selected for processing (1)

• src/env/log_fd/unix.rs

---

📝 Walkthrough

Walkthrough

Unix log file opening and creation now include O_CLOEXEC. LogFd::open derives and reuses the combined permission flags.

Changes

Log file descriptor flags

Layer / File(s)	Summary
Apply close-on-exec flags src/env/log_fd/unix.rs	LogFd::open combines permission flags with O_CLOEXEC. LogFd::create adds O_CLOEXEC to its read/write/create flags.

Estimated code review effort: 2 (Simple) | ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: enabling close-on-exec for log file descriptors.
Linked Issues check	✅ Passed	The changes set O_CLOEXEC when opening and creating Unix log files, directly addressing issue #404.
Out of Scope Changes check	✅ Passed	The four changed lines are limited to adding O_CLOEXEC in the Unix log descriptor open and create paths.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: LykxSassinator, tabokie

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-08-15 11:41:48.752149325 +0000 UTC m=+3478694.788244380: ☑️ agreed by tabokie.
• 2026-08-24 03:08:48.767518587 +0000 UTC m=+471163.938612701: ☑️ agreed by LykxSassinator.