Type Alias: Body2DType

type Body2DType = "dynamic" | "kinematic" | "static";

Pluggable 2D physics backend — its own axis beside the renderer and audio backends. Engine receives one through EngineOptions.physics2D; Physics2DSystem drives it from the Rigidbody2D / Collider2D / Joint2D components. Each implementation lives behind its own subpath export (mmpx/physics-planck, ...) so a game ships only the engine it picked.

The contract is in the solver's units — metres, radians, kilograms, seconds, y up. Physics2DSystem converts from pixels (Physics2DSettings.pixelsPerMeter), so a backend never sees a pixel. Shapes arrive already convex and backend-sized (Physics2D/Collider2DShapes.ts splits polygons).