Measurable Handles: Testing SP3 'Retuning Residuals' in Existing Cosmological Data

If space‑phase behaves like a slowly retuned resonant medium, then current observationsalready force that retuning to be adiabatic, coherent, and nearly dispersionless at leadingorder. That is good news: SP3 does not need messy scattering mechanisms. It also meansany distinctive fingerprints must live in small, smooth residuals—subtle departures fromthe simplest expansion‑only mapping. This appendix provides a practical checklist forhunting those residuals using existing public datasets (supernova time‑stretch, BAOdistance ladders, and CMB temperature‑with‑z), plus guardrails from propagation purity(dispersion limits and GW–EM speed constraints). The goal is to specify ‘what plots toremake’ so that a single retuning function R(z) can be tested consistently across multiplechannels.