[QTI] Saving a question drops data-catalog-idref from its prompt #6307

❌ This issue is not open for contribution. Visit Contributing guidelines to learn about the contributing process and how to find suitable issues.

Target branch: unstable

Observed behavior

• Saving a QTI choice question rewrites <qti-prompt> without its <span data-catalog-idref="…">, even when only a hint changed.
• The item still carries the referenced <qti-catalog> (kept since [QTI] Editing a question keeps the item-level content the editor doesn't write #6290), now with nothing pointing at it.

User-facing consequences

• An imported item's glossary term stops being a glossary term for learners after any edit in Studio.

Steps to reproduce

1. Open a QTI choice item with this prompt and catalog:

   <qti-prompt>Pick the <span data-catalog-idref="g1">vowel</span>.</qti-prompt>
   …
   <qti-catalog id="g1">
     <qti-card support="glossary-on-screen"><qti-html-content><p>A letter like A, E, I, O, U.</p></qti-html-content></qti-card>
   </qti-catalog>

2. Click Edit, expand Hints, click Add hint, type any text, click Close.
3. The emitted raw_data has <qti-prompt><p>Pick the vowel.</p></qti-prompt>.

Context

• Seen on the [QTI] Editing a question keeps the item-level content the editor doesn't write #6290 branch (90c5b6190) in the QTI editor dev demo page, Chromium.

Acceptance Criteria

• Editing any part of such an item keeps data-catalog-idref on the prompt element that carried it.
• Editing the prompt text around such an element keeps the attribute.
• A test covers it from opening the item to the emitted raw_data.

AI usage

Claude Code found this during manual QA of #6290 and drafted the issue.