nx_coindex_bench_gate.nx

nx_coindex_bench_gate.nx -- MEASURED concurrent-writer benchmark for the conflict-free co-index (R-ORCH-2). Exists because the coordinator CAUGHT ITSELF crediting nx_coindex with the WMS's R11 measurement it never individually earned (the exact self-grading the triage v2 forbids). This gate makes it earn a number: 8 FORKED writer processes x 12 appends each, through BOTH paths -- GOOD = ci_append (flock + O_APPEND single-write): must land 96/96, ZERO lost, timed. BAD = the naive read-modify-write a hand-edited shared file degrades to (read whole -> append in memory -> truncate-write whole, no lock, deliberate window): must MEASURABLY lose entries -- the RUN comparator proving the failure mode is real physics, not hypothesis. git = the named external yardstick, STATED by-design (index.lock: concurrent committers serialize-or-FAIL and must retry; the naive path loses SILENTLY; coindex = all land, no retry). GREEN iff good_lost==0 AND bad_lost>0 (the neg-control must fire). Journals the measured line. license_tier: ORIGINAL expect_exit: 0