[QTI] Gap Match interaction #6202

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Overview

Add the Gap Match question type to the QTI editor. An author writes a passage, turns words into gaps (by highlighting them, or by inserting a blank gap and typing its answer into it), and adds optional distractors. Learners drag answers and distractors from one shared pool into the gaps (#5927).

Like inline choice (#6178), it is a passage-based type built on the TipTapEditor seams from #6176. Unlike inline choice, the item is one interaction with one response declaration: the passage sits inside <qti-gap-match-interaction>, and the correct response pairs each answer with its gap.

Scope

Included

• The gap match interaction plugin: its descriptor, parsing, XML assembly and validation.
• The gap node and Insert action in the passage's TipTapEditor, the distractors list, and the editor UI.
• An inline-only mode for TipTapEditor, used for gap answers and distractors ([QTI] Add an inline-only mode to TipTapEditor for gap match choices #6193).

Excluded

• Answer-specific distractor pools (match-group): every answer and distractor is a candidate for every gap.
• Partial credit: an item is scored all-or-nothing.
• Image answers (qti-gap-img) and graphic gap match.
• Mixing gap match with other interaction types in one item.
• Learner preview inside Studio.
• Rendering in Kolibri's QTI viewer (kolibri#15213).

Strategy

• Order. [QTI] Add an inline-only mode to TipTapEditor for gap match choices #6193 (inline-only TipTapEditor) starts once Bring back underline, strikethrough and align support, and remove RTE link support #6151 merges, and [QTI] Gap match interaction: descriptor, parsing, XML assembly and validation #6203 (descriptor, parsing, validation) can proceed in parallel with it. [QTI] Gap match interaction editor, with the gap node and Insert action #6204 (gap node, Insert, distractors and editor UI) depends on both, and can overlap with [QTI] Gap match interaction: descriptor, parsing, XML assembly and validation #6203 once the passage markup is agreed.
• Shared with inline choice. The gap node follows the same pattern as the inline choice chip ([QTI] Inline choice chip and Insert action in the passage editor #6181): an inline node contributed through the [QTI] Update TipTapEditor to support custom insert node behavior defined on parent component #6176 seams, carrying its own data so undo and copy / paste keep it. Whichever lands first sets the pattern for the other.
• Scoring. All-or-nothing, through the standard match_correct template, which the core already writes for a single declaration with a correct response. No change to the editor core is needed.
• Backend. No production change is needed: the server validates against the QTI 3.0 XSD, which includes gap match, and publishes raw_data as-is.
• Kolibri. Studio authoring doesn't wait on kolibri#15213, but the end-to-end check below does.

Testing Requirements

Beyond each task's unit tests, the project is done when a channel with a gap match question (several gaps and distractors) publishes and, once kolibri#15213 lands, renders in Kolibri's QTI viewer, where filling every gap correctly produces SCORE 1 and any wrong gap produces 0.

AI usage

I used Claude Code to draft this tracking issue and its tasks. It read the QTI editor core, the inline choice issues, the QTI 3.0 schema's content model for gap match, and Kolibri's gap match issue to check feasibility. I decided the scope, the scoring and the split, and reviewed and edited the text.