Three-Layer Projection Model: Nested Subjective Spaces R–R₁–R₀ and Middleware Geometry via Central Projection

This paper organizes and integrates the geometric properties of subjective spaces established in the central projection series into a three-layer structure R–R₁–R₀. No new theorems are proved; the paper observes the following structure as a combination of known properties: (1) all subjective spaces share a common origin, (2) they are arranged as concentric nested shells, (3) R-direction displacement between corresponding points is orthogonal to all tangent spaces and hence unmeasurable by any intrinsic metric, and (4) inter-layer maps via central projection are well-defined and regular. This middleware geometry provides an implementation-independent interface between particle internal structure and phase-space dynamics.