Blend the equation, keep the grid honest.

A source-shaped matrix of transparent planes makes custom source and destination factors visible. Every cell uses `CustomBlending`; the equation can mutate across Add, Subtract, ReverseSubtract, Min, and Max without rebuilding the scene.

This route preserves the source-backed custom-blending contract with deterministic local alpha and label fixtures. The official lensflare asset, exact page/pixel fidelity, lil-gui presentation, device/compiler coverage, context-loss stress, and whole-example fidelity remain unverified.