One stress polarization fixed by the displayed vertex

The source mixed Hessian is written exactly in the form (eq:Hessian), with the words “inherited polarized stress tensor” in place of an expansion. The patch fixes that expansion by the explicit vertex calculation. There is now one convention in this paper, not two competing normalizations.

This closes the factor ambiguity for the patch's tensor notation. It does not assert that a located XIV-J theorem had already printed the expansion. Nor does it import a convention from XIV-D or another excluded sheet. The factor is fixed by the displayed functional whose derivative is being taken.