Śrī Yantra: the spherical-to-plane reduction of Rao's constraint system

Frozen, self-contained archive of the bridge between Rao's (1998) spherical Śrī Yantra constraint system and the certified plane system, prior to any spherical enumeration. Contents: a validated spherical engine (`sriyantra.py`), checked against Rao's spherical Table 1; an independent spherical prototype (`spherical_engine.py`) obtained by un-reducing the frozen plane engine, which recovers all 20 plane constraints as the angular scale α → 0; a finite-α audit (`spherical_finite_alpha_audit.py`) showing the two engines agree to 1.3×10⁻¹⁵ across all 20 constraints at Rao's eight published spherical figures (α ∈ [0.23, 1.31] rad); and per-class analytic spine tests. Main result — the reduction law: for each constraint i, Gᵢ(α) = αᵈⁱ · Fᵢ + O(αᵈⁱ⁺²), with leading coefficient exactly the plane constraint Fᵢ, and dᵢ = 2 for the cosine-isosceles constraints {F₃, F₄, F₆} and dᵢ = 1 for the seventeen arc-difference constraints. Proofs for all 20 constraints are in the included note and appendix. Also documents five transcription errata in Rao (1998), including a correction to the printed reduced equation (6.12): tan(rₜ) = x₇ · tan(t/2), not x₇ · (t/2). Source: Rao, C. S. (1998). Śrīyantra — A Study of Spherical and Plane Forms. Indian Journal of History of Science, 33(3), 203–227.