Function produce_element_meshes 

pub fn produce_element_meshes(
    job: &ElementMeshJob<'_>,
    ctx: &MeshProductionContext<'_>,
    opts: &MeshProductionOptions,
    decoder: &mut EntityDecoder<'_>,
    router: &GeometryRouter,
) -> ProducedElementMeshes

THE canonical per-element mesh producer.

Decoder and router are caller-supplied so each pipeline keeps its reuse policy: the native rayon loop builds a fresh seeded decoder + router per element; the browser batch path reuses one warm pair per batch. The decoder MUST have its unit-scale caches seeded (EntityDecoder::seed_unit_scales) — otherwise arc tessellation re-pays an O(file) IFCPROJECT scan per fresh decoder.