With the logical patch to fix T94723, Parsoid can't properly round trip wikitext of the form:
We currently skate by because this is preserved via selser. But if this link is modified in any way, then the external link gets auto-converted to a mw:WikiLink:
This was a reasonable behavior because VE wanted to support cut-and-paste of WP URLs, without importing all of Parsoid's complexity which attempts to recognize all the possible interwiki link URLs and prefixes and convert to a wikilink.
But we need to be more careful about how we apply this wikilink-ification.
I propose that we *only* auto-linkify anchors with type mw:WikiLink. Anything with type mw:ExtLink will be left alone and not wikilinkified.
That is, some links which VE passes to Parsoid and claims are mw:WikiLinks we will serialize as mw:ExtLink (because the URLs do not actually point at interwiki sites). But we will never do the conversion in the other direction, and convert something labelled as a mw:ExtLink into a mw:WikiLink.
As a side effect, this means that edits to a mw:ExtLink in VE must reset the type of mw:WikiLink if you want to enable auto-wiki-linkification. Otherwise, once an mw:ExtLink always a mw:ExtLink.
This is opposite from how VE currently behaves (see comment below).
Alternatively, the entire WikiLink-ification pass could be move to the Parsoid "scrubWikitext" module of VE-specific cleanups.