Planckian dissipation per unit critical entropy as a coupling-free probe of the strange-metal bath

Strange metals pair a resistivity linear in temperature with a specific heat $C/T$ rising logarithmically on cooling. We find that, if electrons scatter off a local critical bath, the coupling cancels in the ratio $Q$ of their coefficients, leaving two measurable numbers: how slowly the bath relaxes, seen in photoemission or optics, and the share of critical entropy that relaxes current. Baths form classes: $Q\le4.91$ for a conformal bath, as SYK models confirm; 9–15 for the Yukawa–SYK field; and far less for Kondo lattices. LSCO, at $Q\approx9$, exceeds the conformal bound, pointing to the Yukawa–SYK field.