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We present optical, near-infrared, and radio observations of supernova (SN)
SN~IIb 2022crv. We show that it retained a very thin H envelope and
transitioned from a SN~IIb to a SN~Ib; prominent H$\alpha$ seen in the
pre-maximum phase diminishes toward the post-maximum phase, while He {\sc i}
lines show increasing strength. \texttt{SYNAPPS} modeling of the early spectra
of SN~2022crv suggests that the absorption feature at 6200\,\AA\ is explained
by a substantial contribution of H$\alpha$ together with Si {\sc ii}, as is
also supported by the velocity evolution of H$\alpha$. The light-curve
evolution is consistent with the canonical stripped-envelope supernova subclass
but among the slowest. The light curve lacks the initial cooling phase and
shows a bright main peak (peak M$_{V}$=$-$17.82$\pm$0.17 mag), mostly driven by
radioactive decay of $\rm^{56}$Ni. The light-curve analysis suggests a thin
outer H envelope ($M_{\rm env} \sim$0.05 M$_{\odot}$) and a compact progenitor
(R$_{\rm env}$ $\sim$3 R$_{\odot}$). An interaction-powered synchrotron
self-absorption (SSA) model can reproduce the radio light curves with a mean
shock velocity of 0.1c. The mass-loss rate is estimated to be in the range of
(1.9$-$2.8) $\times$ 10$^{-5}$ M$_{\odot}$ yr$^{-1}$ for an assumed wind
velocity of 1000 km s$^{-1}$, which is on the high end in comparison with other
compact SNe~IIb/Ib. SN~2022crv fills a previously unoccupied parameter space of
a very compact progenitor, representing a beautiful continuity between the
compact and extended progenitor scenario of SNe~IIb/Ib.