Two instruments on one null: the reported multifractality of the human heartbeat, re-audited

A large clinical and complexity-science literature quotes multifractal detrended-fluctuation-analysis (MFDFA) widths of physiological signals as evidence of nonlinear, cascade-like dynamics, and reads a width that does not exceed its phase-randomised (IAAFT) surrogate band as evidence that a signal is monofractal, linear, or "not a cascade." We show, on the human heartbeat, that this reading is an artifact of the width estimator's own low power, not a property of the heart. We run two detection statistics on the byte-identical IAAFT null — regenerated from the same pinned surrogate seeds, so only the statistic differs — across four canonical PhysioNet RR cohorts. Instrument one is the field-standard MFDFA two-point width; instrument two is a wavelet-scattering-moment omnibus (sparsity, normalised second-order scattering, cross-scale modulus correlation, and one phase/modulus time-asymmetry coordinate proven exactly odd under time reversal), with a pre-registered specificity and power battery. Under the width, healthy-cohort multifractality mostly collapses against the matched linear null (nsr2db: 19/54 records significant under NN editing, median IAAFT z = 0.60), while the congestive-heart-failure cohort retains it (chf2db: 18–25/29). Under the scattering omnibus, on the same surrogates, the healthy collapse does not harden — it inverts: decisive excess on 54/54 healthy records (both editing policies), carried predominantly by time-irreversibility (median aggregate z 73 under NN, significant on 53/54), with a real secondary intermittency component; the CHF cohort is 29/29, carried instead by the multiplicative sparsity / second-order families. The specificity battery places the linear-control false-positive rate at 0.010 (nominal 0.030) and the power curve reaches 16/16 at Holter length. The width's healthy null result was therefore a statement about the width estimator's power on this cohort; a sharper instrument, on the identical null, rejects the same records. This is the physiological instance of the program's finding that the width/IAAFT pairing is incoherent (canon §6.2): a null width-vs-IAAFT result is never, on its own, evidence of linearity. We read the live t_MF robustness counterclaim head-on against its own reported cascade split (§7). All results reproduce from a fresh clone behind a deterministic gate. Nothing here is clinical; time-irreversibility is a documented physiological feature, and every statement is a measurement about public, de-identified datasets. Calibration note. The specificity battery is 96 exact rank tests of per-test size 1/33 with 1 significant: that is consistent with the nominal 0.030 (expected 2.9; P = 0.21). It certifies the instrument is not anti-conservative and has no power to establish that it is conservative. Companion preprint. The program-level mechanism, the pincer, and the synthetic known-truth power/specificity certificate are not re-derived here; they are owned by the sibling methods-core preprint "The width and the null" (Zenodo DOI reserved; publication pending), of which this paper is the physiological instance. The reference list was verified against Crossref on 2026-08-30 and is fully discharged; three bibliographic errors were corrected in that pass. Part of the Feno program. The source repository is private; the reproduction materials for this record are contained in the record itself. Version 2 (2026-09-01): reference-list publication-status notes corrected (the program's reserved DOIs were published 2026-08-31); content otherwise unchanged. Version 3 (2026-09-15). The paper now cites the Feno-program records it reads by their concept DOIs, records the deposit of Fenosoma record v5 (10.5281/zenodo.22759709) and record v10 (10.5281/zenodo.22759711, the recovery floor re-measured as the pair (N, fit grid)), and is rebuilt from the repository source so the deposited copy matches it. No measured number changes.