hyperref redefinition of `\contentsline` adds one level of braces if `linktoc=page`

In the definition of \contentsline, there is the following

8636 \def\Hy@temp{#3}%
8637 \ifx\Hy@temp\ltx@empty
8638 \csname l@#1\endcsname{#2}{#3}%
8639 \else
8640 \csname l@#1\endcsname{{#2}}{%
8641 \hyper@linkstart{link}{\Hy@tocdestname}{#3}\hyper@linkend
8642 }%
8643 \fi

This is triggered by linktoc=page option.

The issue (if there is one) is the {{#2}} at code line 8640. This is the only location in \contentsline definition where #2 ends up wrapped this way.

This makes it harder to see if #2 starts with \numberline or variants (depending on document class). In fact this causes a bug in etoc (a bug which was there since initial release of etoc), which does not detect the \numberline and leaves it in \etocname, thus it delayed expansion (which depends on then current setting of \@tempdima) causes varying effect. This surfaced in an issue in yathesis.

Is there any reason for the added braces?

Start at hyperref's \contentsline definition around code lines 8636–8642 and reproduce the behavior with linktoc=page, checking how the added braces affect #2 and \numberline. Compare the result with etoc's handling and determine whether the braces are required; done means the behavior is corrected or the reason is documented with a regression test.