fix(startup): auto-raise file descriptor soft limit to prevent "Too many open files"

[vparfonov]

Summary

Many systems default the RLIMIT_NOFILE soft limit to 1024 (Linux) or 256 (macOS), which is too low for Vector when it monitors large numbers of log files - common in Kubernetes environments. This causes "Too many open files (os error 24)" crashes.

This PR raises the soft file descriptor limit to the hard limit at Vector startup, before any sources open files. On macOS, where the hard limit can be RLIM_INFINITY (which setrlimit rejects), Vector falls back to the kernel-enforced kern.maxfilesperproc (typically 10240).

Changes:

• Cargo.toml: add libc dep and "resource" feature to nix for rlimit access
• src/cli.rs: call raise_file_descriptor_limit() in init_global() before metrics init,with macOS kern.maxfilesperproc fallback

Vector configuration

No configuration changes — this runs unconditionally at startup

How did you test this PR?

Unit tests: 3 tests in cli::tests (raise limit, already-at-max, macOS sysctl)

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

• Closes: Limit number of open files at the same time #14818
• Related: fix(sources): prevent "Too many open files" by raising FD limits and adding LRU eviction #25241 (original combined PR, split per reviewer feedback)

Notes

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[pront]

Should we expose this option as a CLI argument instead? We can consider changing the default behavior later, it needs some more consideration.