The goal of this task is that Parsoid includes data-mw on the reflist <li> as the source of truth for footnote body content.
Background
Parsoid will render a main+details ref by putting the main ref footnote body into the reference list's data-mw attribute. Wikitext such as:
<ref name="main" details="{{1x|wrapped details text}}">{{1x|wrapped text}}</ref>Is rendered as:
<p id="mwAg"><sup about="#mwt2" class="mw-ref reference" id="cite_ref-2" rel="dc:references" typeof="mw:Extension/ref"
data-mw="{"name":"ref","attrs":{"name":"main","details":"{{1x|wrapped details text}}"},"body":{"id":"mw-reference-text-cite_note-2"},"mainRef":"main","isSubRefWithMainBody":1}"><a
href="#cite_note-2" id="mwAw" title=""><span class="mw-reflink-text" id="mwBA"><span class="cite-bracket"
id="mwBQ">[</span>1.1<span class="cite-bracket" id="mwBg">
]</span></span></a></sup></p>
<div class="mw-references-wrap" typeof="mw:Extension/references" about="#mwt4" id="mwBw"
data-mw="{"name":"references","attrs":{},"autoGenerated":true,"body":{"html":"\n<sup typeof=\"mw:Extension/ref\" data-parsoid=\"{}\" data-mw='{\"name\":\"ref\",\"attrs\":{\"name\":\"main\",\"group\":\"\"},\"body\":{\"id\":\"mw-reference-text-cite_note-main-1\"},\"isSyntheticMainRef\":1}'><span about=\"#mwt1\" typeof=\"mw:Transclusion\" data-parsoid=\"{}\" data-mw='{\"parts\":[{\"template\":{\"target\":{\"wt\":\"1x\",\"href\":\"./Template:1x\"},\"params\":{\"1\":{\"wt\":\"wrapped text\"}},\"i\":0}}]}'>wrapped text</span></sup>"}}">
<ol class="mw-references references" id="mwCA">
<li about="#cite_note-main-1" id="cite_note-main-1" data-mw-footnote-number="1"><span rel="mw:referencedBy"
class="mw-cite-backlink" id="mwCQ"></span> <span id="mw-reference-text-cite_note-main-1"
class="mw-reference-text reference-text"><span about="#mwt1" typeof="mw:Transclusion" id="mwCg"
data-mw="{"parts":[{"template":{"target":{"wt":"1x","href":"./Template:1x"},"params":{"1":{"wt":"wrapped text"}},"i":0}}]}">wrapped
text</span></span>
<ol class="mw-subreference-list" id="mwCw">
<li about="#cite_note-2" id="cite_note-2" data-mw-footnote-number="1.1"><span class="mw-cite-backlink"
id="mwDA"><a href="#cite_ref-2" rel="mw:referencedBy" id="mwDQ" aria-label="Jump up" title="Jump up"><span
class="mw-linkback-text" id="mwDg">↑ </span></a></span> <span id="mw-reference-text-cite_note-2"
class="mw-reference-text reference-text"><span about="#mwt3" typeof="mw:Transclusion" id="mwDw"
data-mw="{"parts":[{"template":{"target":{"wt":"1x","href":"./Template:1x"},"params":{"1":{"wt":"wrapped details text"}},"i":0}}]}">wrapped
details text</span></span></li>
</ol>
</li>
</ol>
</div>When wikitext is nontrivial, data-mw is also added reflist list items. It's clearest when using a template:if the footnote body contains {{1x|main body}} then the reflist item contains the transclusion data.
Outcome
In Cite Parsoid, RefTagHandler has always called extTagToDOM which renders the ref tag as a <sup> containing wikitextToDOM of the ref body wikitext. The sup's firstChild (the footnote body) is copied into the reflist and includes data-mw.
This even works inside of a template-produced {{reflist}}.
It also works for subrefs, whose content Cite produces directly using wikitextToDOM stored by a separate code path in externalFragment—still correctly including data-mw.