Function resident_bytes_now 

pub fn resident_bytes_now() -> u64

Resident set size of this process in bytes, or 0 when unknown.

Linux (/proc/self/statm) covers every production target (Docker, Railway, the three release binaries). Other platforms return 0, which leaves the RSS breaker inert on dev machines - the admission semaphores still bound memory there. Kept behind this helper so the source can be swapped (e.g. for jemalloc stats) without touching call sites; the allocator swap itself was deliberately skipped because the release matrix includes a musl target where jemalloc is a known build risk.