nx_sts_rowwrite_gate.nx

nx_sts_rowwrite_gate.nx -- THE TEETH OF ROW-LEVEL PLANE WRITES (loadgov LV17 sts_put_append, 2026-09-02). In-process over nx_store_seed_lib on a /tmp fixture plane (created at SETUP with sys_mkdir; the fixture-ratchet law: never a production prefix). What is proven: sts_find_seq locates a row by its first column and refuses an absent id; sts_append_fast adds one row and the reader sees it last; sts_replace_fast overwrites exactly one row at its seq, keeps count and order, and newest-wins across two replacements; an out-of-range seq is refused with the plane untouched. NOT proven here: the O(1) cost. It holds BY CONSTRUCTION (each write is one ss_add + one commit) and the honest measure of it is the D-state roster under load, which is nx_dstate's job, not a unit gate's. Inherits nx_gate_verdict: the exit code IS the verdict; every neg-control is NAMED for the gatelaw census. license_tier: ORIGINAL No hw writes (Rule 26). expect_exit: 0