nx_browser_struct_col_gate.nx

nx_browser_struct_col_gate.nx -- the BR2 structural-exactness column, proven IN PROCESS. Subject: nx_browser_struct_col_lib.nx, IMPORTED (not forked), so every tooth here sits inside the mutation harness's build closure and a planted defect in the lib actually kills a mutant. A gate that exec'd the promoted census binary would read NOT-REACHED for every mutant and its GREEN would mean nothing. The three things this gate exists to stop, each measured on real data on 2026-08-26 BEFORE it was written, so no tooth here is a hypothetical: 1. A permil computed over TWO oracle bands published as "1000" (goog_raw.html), and a permil computed over ZERO oracle bands published as "0" (so_aug.html, x_aug.html). Both are arithmetic on an empty subject wearing a number -- a perfect score and a total failure, neither of them evidence. 2. A bar reported MET on partial coverage -- one bar site measured out of the four the browser.plan done-rule names. 3. A CSS-ON/CSS-OFF flip taken on a difference smaller than the census's own measured variance. license_tier: ORIGINAL No hw writes (Rule 26).