generate-publish parser docs markers

Trap: counting only exact generated-doc markers looks sufficient because a valid BEGIN/END pair is unique, but duplicate or malformed marker-like fragments (such as <!-- BEGIN GENERATED TITLE GRAMMAR -- >) leave the generated region ambiguous. Fix: reject missing, duplicate, malformed, or marker-like BEGIN/END delimiters before replacement or comparison; require one ordered authoritative pair and regression-test valid markers plus malformed extras.