  For functions $f$ with Fourier transform supported in the truncated cone, we
bound superlevel sets $\{x\in\mathbb{R}^3:|f(x)|>\alpha\}$ using an
$\alpha$-dependent version of the wave envelope estimate of Guth--Wang--Zhang.
Our estimates imply both sharp square function and decoupling inequalities for
the cone. We also obtain sharp small cap decoupling for the cone, where small
caps $\gamma$ subdivide canonical $1\times R^{-1/2}\times R^{-1}$ planks into
$R^{-\beta_2}\times R^{-\beta_1}\times R^{-1}$ sub-planks, for
$\beta_1\in[\frac{1}{2},1]$ and $\beta_2\in[0,1]$.
