E5: carrier check of the assembled coefficient

$Q_H{\mathcal{C}}_{3,\mathrm{D}}\in {\mathcal{E}}_H$ is XII-D's. The scalar-only completion ${{\mathcal{A}}_2}^{\mathrm{sc}}(\gamma ,0;\varphi )$ is a different kernel, not in XII-A's named sector (${\mathcal{B}}_f$ has degree $(1,1)$, $\mathcal{T}$ has degree $(0,3)$). Its admission is proved here by an explicit calculation; XII-D's bound for $t_{\mathrm{D}}$ is not cited for it.