@ArthurTaylor and I looked into this, and eventually arrived at some promising-sounding investigation results. The most important is that in this code:

<cdx-lookup
    v-model:selected="selection"
    :placeholder="messages.getUnescaped(
        'wikibaselexeme-newlexeme-lemma-language-placeholder-with-example',
        config.placeholderExampleData.spellingVariant
    )"
    :search-input="searchInput"
    :menu-items="menuItems"
    :input-value="props.modelValue"
    @input="onInput"
    @update:selected="onOptionSelected"
>

:search-input="searchInput" appears to have no effect – the Wikit component had this prop, but the Codex component does not. By comparison, the ItemLookup component sets v-model:input-value="searchInputWrapper". Both the ItemLookup and the SpellingVariantInput have two props of their own, for the value and the search input, but ItemLookup binds Codex’s value to the search input prop, whereas SpellingVariantInput binds Codex’s value to its own value and the search input prop goes nowhere. We want to try to bring SpellingVariantInput closer to ItemLookup – bind Codex’s value to the search input prop, and manage the SpellingVariantInput’s value separately (with lastSelectedOption and the update:modelValue event).

Added a PR https://github.com/wmde/new-lexeme-special-page/pull/800 that reflects that approach and seems to work.

Needs some more work, unfortunately.

The above error was not reproducible in the dev entry point, which turns out to be because in the dev entry point we were still using Codex 1.14, whereas MediaWiki now ships Codex 1.16. After updating the new-lexeme-special-page repo to Codex 1.16, the error becomes reproducible in the dev entry point (and some tests start failing).

git bisect shows that the difference in behavior was introduced with Lookup: Ensure input event on selection has correct value (T378177). We still need to investigate what this means and if we need a fix in new-lexeme-special-page and/or in Codex.

Steps to reproduce:

• check out new-lexeme-special-page
• npm install
• npm install @wikimedia/codex@1.16.0
• npm run test:integration

(I can’t fully test these steps because npm is glacially slow for me, but they should work, I think.)

Added PRs https://github.com/wmde/new-lexeme-special-page/pull/801 and https://github.com/wmde/new-lexeme-special-page/pull/802 to adjust the SpellingVariantInput behaviour to the new codex implementation.