nx_css_vars.nx

nx_css_vars.nx -- CSS custom-property (var()) resolution for the SOVEREIGN render engine, so Nishi Browser + the reader + NishiOS render the fleet-standard --nx-color-* design tokens NATIVELY (operator 2026-07-10: "build nishi os and nishi browser first, not into javascript until last-mile on 3rd-party"). The native engine parsed only #hex/rgb(); every fleet-bar page is built on var(--token), so without this our own browser renders them colorless while Waterfox looks perfect -- the exact inversion to kill. PURE LIB (no main). One entry: cx_expand(inp,n,out,outcap) -> a byte copy of the CSS with every var(--x) substituted by its :root definition (FIRST-wins, so base/light tokens beat later dark overrides; recursive so a token defined as var() of another resolves; var(--x,fallback) supported; nested rgb() parens balanced). GUARANTEED no-op when the CSS has no var() -> existing pages/gates stay byte-identical. Wired as the final pass of rh_filter_media (nx_render_html) so all three native surfaces get it from one point. Consumers: nx_render_html (via rh_filter_media) + gate nx_css_vars_gate. license_tier: ORIGINAL