Function auto_limit 

pub fn auto_limit() -> usize

Auto formula: CPUs × oversubscribe vs free-RAM budget, clamped.

When free RAM is unknown (non-Linux /proc path), the CPU budget is further clamped by NON_LINUX_CPU_CAP so low-RAM macOS/Windows hosts do not oversubscribe solely from cpus × IO_OVERSUBSCRIBE (G-PAR-25).