Subject–Object–Boundary Geometry: From Observer, Perturbing Object and Interface Coupling to Projection Possibility

Proposes subject–object–boundary geometry Γ = ⟨S, O, boundary⟩: a closure shown only under a fixed observer and boundary is merely a 'conditional closure'; mirror tests need label maps (§52 uses B3 ↔ B5 as an example); it also gives a triadic perturbation and an 'SOB certificate'. Lebesgue appears only in §100–102.