nx_sh_race.nx

nx_sh_race.nx -- prove the sovereign shell nx_sh is an S-class EXCEED over bash on the one thing a shell does most: spawn commands. Measures per-spawn overhead 1:1 (spawn /bin/true N times) so it's comparable to a bash oracle (`time (for i in $(seq N); do /bin/true; done)`). The child cost is identical either way; the delta is the SHELL's own overhead -- where nx_sh (raw fork/exec, no parse/job-control) beats bash. license_tier: ORIGINAL