Companion

Always include the sightline splice. hasActiveSightline is set inside RealtimeSightline.makeDrawable during the render-traversal phase — the same phase 3D-Tiles layers traverse — so its value at shader-pick time depends on layer order. With the splice always present, computeSightlineTint early-outs to vec4(0.0) when applySightline == false, so per-fragment cost when no sightline is live is one uniform branch + no texture lookups.