Change Cite reference pipeline to use an intermediate file

Another instance of this bug: https://de.wikipedia.org/w/index.php?title=Rothschild_(Familie)&diff=prev&oldid=264904033 (but this dirty diff looks even more broken because the reference also uses a template). Reproduced in my sandbox: https://de.wikipedia.org/w/index.php?title=Benutzer%3AJohannes_Richter_%28WMDE%29%2FTest3&diff=264904468&oldid=264904457

I made a first draft how the gadget at https://en.wikipedia.org/wiki/MediaWiki:Gadget-ReferenceTooltips.js can be updated:

I looked into how the Parsoid problem could be solved. What comes to mind first is to adapt the community CSS in a similar way as in the legacy parser (i.e. only add the brackets when there actually are backlinks). While this might actually be solvable with the :empty selector (see MDN) I found a much more straightforward solution: https://gerrit.wikimedia.org/r/1247440

Change #1247440 had a related patch set uploaded (by Thiemo Kreuz (WMDE); author: Thiemo Kreuz (WMDE)):

[mediawiki/extensions/Cite@master] Remove empty backlink <span> from Parsoid output

https://gerrit.wikimedia.org/r/1247440

Thanks a lot for the quick response, that's super helpful. Yes, we are already experimenting with a few possible options including more compact or collapsible sub-ref lists. T413221 is a placeholder ticket for that.

It's not really about whether SFN is more or less compact. It's about how it feels. Mostly empty space between subrefs immediately feels less compact because there is more empty space. It's about look & feel, not about physical pixels, if that makes sense.

I would like to understand better how {{sfn}} is "less compact" (?) than the sub-referencing syntax. When I look at one of the latest revisions without sub-references at https://pl.wikipedia.org/wiki/Ali_Chamenei?oldid=79197159#Przypisy there is a total of 45 individual references + 2 entries in the bibliography section. "Axworthy 2004" appears 25 times and "Coville 2009" 8 times. There are 12 + 2 = 14 main refs.

In T418280#11662368, @Johannes_Richter_WMDE wrote:

We noticed that https://sv.wikipedia.org/wiki/MediaWiki:Gadget-referenser.css also introduces square brackets in Parsoid view. Proposed fix (consistent with the community removing the square brackets in MediaWiki:Cite references link many):

Change lines 14-19 from:

span[rel="mw:referencedBy"]::before {
    content: "^ [";
}
span[rel="mw:referencedBy"]::after {
    content: "]";
}

To:

span[rel="mw:referencedBy"]::before {
    content: "^ ";
}

-> Delete lines 17-19 entirely and remove the square bracket from line 15.

It looks like we mistakenly closed T388762 without implementing it for Parsoid. We probably only need a single line to fix that:

$extApi->addTrackingCategory( 'cite-tracking-category-ref-details' );

See T372709 for inspiration.