Dimensionless Coherence Ratio for a Toroidal-Constraint Fermi Mechanism

This technical note defines a dimensionless coherence ratio r governing interstellar signal detectability and evaluates whether a toroidal cosmological modulation term r_T contributes an independent constraint beyond known propagation physics. The note establishes the factorisation r_total = r_ISM · r_disp · r_scint · r_CMB · r_T, locks the functional form R(t) and timescale τ, derives band-bounded distinguishability floors for ε, and identifies residual observables and falsifiers. One open parameter remains: coupling depth ε, explicitly declared. Classification: speculative program with explicit modulation model and band-bounded distinguishability condition. Keywords: Fermi paradox, coherence bandwidth, toroidal cosmology, interstellar signal propagation, dimensionless modulation, falsifiable constraint