A minipage originating in {<start>} part of a custom line style causes tagging warnings

[jfbu]

This test file raises warnings on second compilation from the minipage inside the subsection line style (the minipage originate in this line style via its {<start>} first argument, is executed on the first subsection toc line after a section toc line).

Package tagpdf Warning: Parent-Child 'Sect/' --> 'TOCI/pdf'.
(tagpdf)                Relation is not allowed (struct 174, /Div --> struct
(tagpdf)                192) on line 50

Related: #4

Indicates probably I was wrong after fixing #4 to reactivate the minipage tagging sockets for the contents.

[jfbu]

Failure on 2025-09-20 with tagging HEAD at 2d5d2e2 look like this for the related tests:

• gh05_other_test_for_minipage.tex, on fourth pdflatex pass with tagpdf warnings made into errors:

! Package tagpdf Error: Parent-Child ':Reference' --> ':Part'.
(tagpdf)                Relation is not allowed! on line 48
(tagpdf)                struct 177, Reference --> struct 178, text-unit

• gh05_warnings_from_minipage.tex under same circumstances:

! Package tagpdf Error: Parent-Child ':Reference' --> ':Part'.
(tagpdf)                Relation is not allowed! on line 46
(tagpdf)                struct 177, Reference --> struct 178, text-unit

Similar warnings happen with next two files, also at the fourth compilation with warning turned into error.

• gh10_parbox.tex, (see Simplest line style using \parbox creates warnings #10)
• test_tagging_toc_as_molecule_b.tex.