nx_srcset_lib_gate.nx

nx_srcset_lib_gate.nx -- the referee for BR14 (nx_srcset_lib, symbol bi_srcset). IN-PROCESS BY CONSTRUCTION. It imports the subject and the render core it is wired into, so the subject is inside THIS gate's own build closure and a mutation of nx_srcset_lib.nx reaches these teeth. A gate that fork/execs a deployed elf cannot be mutation-proven -- every mutant reads NOT-REACHED -- so nothing here forks anything. =================================================================================================== THE ACCEPT RULE, PRE-DECLARED BEFORE THE FIRST RUN (written 2026-08-26, before any result existed). BR14 is proven by this gate IF AND ONLY IF all five hold; anything less is reported NOT PROVEN by name, and the rung stays open. A. GRAMMAR. Every documented descriptor form selects the candidate the HTML selection algorithm selects, for a target DERIVED from the viewport and the device pixel ratio -- not from any breakpoint written in this estate. B. DISCRIMINATION. The three trivial wrong implementations -- always-take-the-first candidate, always-take-the-last, always-take-the-largest -- each FAIL at least one tooth. A ruler that cannot be distinguished from taking the first item has measured nothing. C. WIRING. An <img> whose only usable URL lives in srcset / data-src / data-srcset resolves to THAT URL through the real br_layout, i.e. page.bsrc_off names it. Proving the lib in isolation proves a function, not a browser. D. NO REGRESSION. An <img> carrying only a plain src resolves to byte-identically the range the pre-BR14 code chose, checked against an INDEPENDENT instrument (nx_dom_find_attr direct). E. PAINTED, NOT MERELY SELECTED. On a fixture page whose figures are lazy and responsive, imgsrc_laid == decoded == painted: every laid-out <img> box decodes through the real image path and leaves its own pixels in the framebuffer. This is the done-rule's SHAPE on a fixture this gate controls. It is NOT the done-rule's live half (the wikipedia benchmark page over the network), which needs the GUI and a network and is NOT claimed here. ===================================================================================================