USSFT Paper XVII: Observational Signatures: Mapping Framework Predictions to Current and Projected Experimental Sensitivity

Paper XVI cataloged the experimental predictions of the USSFT framework with their theoretical magnitudes and status classifications. This companion paper maps those predictions to specific observational programs, quoting current best bounds and projected sensitivities from operating and forthcoming instruments. For each prediction we compute the "safety margin" - the number of orders of magnitude separating the USSFT-predicted effect from current or projected experimental reach. We find that most Planck-scale USSFT corrections remain safely beyond current sensitivity by many orders of magnitude, a situation shared with all quantum gravity frameworks operating at ESRI approximately EPl. The most promising near-term contact points are: (i) improved Lorentz-invariance violation bounds from gamma-ray burst timing, which continue to tighten the quadratic LIV window; (ii) late-time cosmological probes (BAO, SNIa, CMB lensing) that could constrain or detect departures from LambdaCDM of the form predicted by USSFT's Gₑff (z) if the (C) -level parameter delta₀ is eventually derived from first principles; (iii) next-generation CMB experiments (LiteBIRD, CMB-S4) that will measure the inflationary observables nₛ and r to precisions sufficient to either confirm or falsify the USSFT predictions nₛ approximately 0. 957-0. 964 and r approximately 0. 003-0. 006 derived in Paper XIII via the xi-inflation mechanism; and (iv) gravitational-wave echo searches in next-generation detectors, which directly probe the near-horizon structure predicted by the entropic bounce mechanism. This is the seventeenth paper in the 18-paper USSFT technical series; it builds on the prediction catalog of Paper XVI (DOI: 10. 5281/zenodo. 19778147) and the inflationary observables of Paper XIII (DOI: 10. 5281/zenodo. 19690229). For a conceptual overview, see Paper 0 (DOI: 10. 5281/zenodo. 17852167, published in Int. J. Quantum Found. 12 (2), 667-718, 2026).