  AT 2022cmc is a luminous optical transient ($\nu L_{\nu} \gtrsim 10^{45}$ erg
s$^{-1}$) accompanied by decaying non-thermal X-rays (peak duration $t_{\rm X}
\lesssim$ days and isotropic energy $E_{\rm X,iso} \gtrsim 10^{53}$ erg) and a
long-lived radio/mm synchrotron afterglow, which has been interpreted as a
jetted tidal disruption event (TDE). Both an equipartition analysis and a
detailed afterglow model reveals the radio/mm emitting plasma to be expanding
mildly relativistically (Lorentz factor $\Gamma \gtrsim\,few$) with an opening
angle $\theta_{\rm j}\simeq0.1$ and roughly fixed energy $E_{\rm j,iso} \gtrsim
few \times 10^{53}$ erg into an external medium of density profile $n \propto
R^{-k}$ with $k \simeq 1.5-2$, broadly similar to that of the first jetted TDE
candidate Swift J1644+57 and consistent with Bondi accretion at a rate $\sim
10^{-3}\dot{M}_{\rm Edd}$ onto a $10^{6}M_{\odot}$ black hole before the
outburst. The rapidly decaying optical emission over the first days is
consistent with fast-cooling synchrotron radiation from the same forward shock
as the radio/mm emission, while the bluer slowly decaying phase to follow
likely represents a separate thermal emission component. Emission from the
reverse shock may have peaked during the first days, but whose non-detection in
the optical band places an upper bound $\Gamma_{\rm j} \lesssim 100$ on the
Lorentz factor of the unshocked jet. Although a TDE origin for AT 2022cmc is
indeed supported by some observations, the vast difference between the
short-lived jet activity phase $t_{\rm X} \lesssim$ days relative to the
months-long thermal optical emission, also challenges this scenario. A stellar
core-collapse event giving birth to a magnetar or black hole engine of peak
duration $\sim 1$ day offers an alternative model also consistent with the
circumburst environment, if interpreted as a massive-star wind.
