TOC Generation broken with newer Sphinx versions

[aanagnosastronauticscom]

Sphinx version 8.1.3 things work fine the TOC links look sane, and the subsections get page numbers.

      <li class="toctree-l1">
       <a class="reference internal" href="#document-Feature reStructuredText Environment">
        5. Feature reStructuredText Environment
       </a>
       <ul>
        <li class="toctree-l2">
         <a class="reference internal" href="#setup">
          5.1. Setup
         </a>

Sphinx 8.2.0 and newer up to 8.2.3 (current as of filling), sub section do not get numbers, and, the links are malformed. (href)

      <li class="toctree-l1">
       <a class="reference internal" href="#document-Feature reStructuredText Environment">
        5. Feature reStructuredText Environment
       </a>
       <ul>
        <li class="toctree-l2">
         <a class="reference internal" href="#document-Feature reStructuredText Environment#setup">
          5.1. Setup
         </a>

[kreuzberger]

I tried to find out why and when this could be fixed and found: sphinx-doc/sphinx#13739. This could be a related bugfix for this issue.

[gastmaier]

My fix may solve the issue. It makes sure that IDs are unique before refs resolution. Feel free to try to raise awareness with the maintainers.