"Less than" symbol breaks mathjax

Anki Desktop
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I’m currently running on last version of main I downloaded, f61c64dd3408670a23ef035b623af69d50e8ec7d , on ubuntu. All addons disabled

Reproduction step:

  • Open a note
  • In a field, open the mathjax editor, and enter “a<b”.
  • Leave the mathjax editor

Expected result:

  • Seeing “a<b” in mathematical notation in the field

Actual result

  • seeing “a<b” in the field for a second
  • see “a” in the field

Investigation:

  • Open the html editor
  • Enter a lot of spaces (because otherwise the mathjax editor hides the html editor)
  • Open the mathjax editor. Type “a<”, you’ll see in html “a<”
  • type “b”, you’ll see that “&lt” disappeared and “b” never appeared

So it seems that if < is not the last symbol, it disappear with everything after it.
My guess is that it’s related to the meaning of < in html.

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added to mathjax editor confused by opening angle bracket · Issue #1665 · ankitects/anki · GitHub

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Workaround: Use \lt instead of <, or leave a space after <. I’ll also take a look, if there’s a good way to deal with it otherwise (probably needs escaping at some point).

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I indeed used \lt in order to move on.
I assume you don’t plan it to be the long term solution here.
The main trouble is that the text after < disappears with no warning. I went on and edit a different field. It’s only by luck that I double-checked a previous field and realized something was off. Which means a lot of people will miss the issue and maybe won’t know how to correct it (I thought about it after maybe a minute or two. Admittedly, I spent the time investigating whether the bug was reproducible without add-on to write this forum post instead of just going on with my note)

A lesser trouble is that, even in a word where I always recall to use lt, I still have tons of notes which use < in mathjax, and that suddenly makes them risky to edit, as I may not think about checking whether they use < or lt, and not think about replacing < with lt immediately.
I could replace all [$]…<…[/$] using regexp, but honestly, doing a huge search and replace with regexp mostly sounds the good way to make disastrous irreversible change (Or maybe I’m just paranoid because I lost 10k cards two weeks ago due to a broken script and it took me hours to revert using a backup)

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