What is the test for reversal of a judgment against a defendant who was found guilty of a violation of the Sixth Amendment's confrontation right?

We must now decide whether this constitutional violation mandates reversal. "Violation of the Sixth Amendment's confrontation right requires reversal of the judgment against a criminal defendant unless the prosecution can show beyond a reasonable doubt that the error was harmless. [Citations.]" ( People v. Rutterschmidt (2012) 55 Cal.4th 650, 661, 147 Cal.Rptr.3d 518, 286 P.3d 435.) This is a stringent standard. Indeed, the prosecution must prove the jury's verdict was surely unattributable to the evidence that resulted from the violation. ( People v. Pearson (2013) 56 Cal.4th 393, 463, 154 Cal.Rptr.3d 541, 297 P.3d 793.) If there is a reasonable possibility the evidence contributed to the verdict, we must reverse. ( People v. Reese (2017) 2 Cal.5th 660, 671, 214 Cal.Rptr.3d 706, 390 P.3d 364.)