WS-2 items 4+5: draw structure on canvas + preserve N-deep tree on save

Round-trip fix (item 5): serializeCanvasShapes no longer re-derives the question
tree from boundary pairs (which flattened 3-deep → 2-tier). The whole tree is now
carried as 'part' shapes that hold parentId + isContainer + depth; save preserves
the real parent_id chains (persisted parent wins; geometry is only a fallback for
manually-drawn shapes). Boundary-pair synthesis is kept but attaches to a covering
container box when one exists. New test locks a 3-deep Q→part→subpart round-trip.

Draw structure (item 4): shapesFromTemplate now draws containers too (were skipped),
each with nesting depth. examCanvasShapes renders container frames (transparent,
depth-hued border), PRINTS MARKS on part/container boxes (◆N pill; were never
drawn), and NAMES context figures (figure name as label + description tooltip +
'→ Q' tether pill; was an anonymous purple box). Context name/description round-trip
via exam_response_areas.meta.

Threads new shape props through the tldraw util + setup page + types. Adds meta to
ExamResponseArea + replace payload. tsc: no new errors; 7/7 model tests pass.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_01GruxHXxfdp4kZCgAMVFgvV

src/utils/exam-canvas/model.ts

@@ -26,6 +26,16 @@ export interface ExamCanvasShapeModel {
   responseForm?: 'lines' | 'answer-box' | 'working' | 'diagram' | 'tick-boxes' | 'table' | 'blanks'
   contextType?: string
   questionId?: string | null
+  /** Tree parent (container question) id — preserved across a round-trip so N-deep structure survives a save. */
+  parentId?: string | null
+  /** True for a container question (main question / intermediate part) drawn as a nesting box. */
+  isContainer?: boolean
+  /** 0 = main question, 1 = part, 2 = subpart … drives nesting styling. */
+  depth?: number
+  /** Figure/table caption for a context region (shown as a tooltip). */
+  description?: string
+  /** Label of the owning question, for a context region's visible tether pill. */
+  linkLabel?: string
   source?: ExamTemplateSource
   confirmed?: boolean
   confidence?: number | null
@@ -118,34 +128,69 @@ export function serializeCanvasShapes(template: ExamTemplateDetail, shapes: Exam
   const orderedBoundaries = shapes
     .filter((s) => s.kind === 'boundary')
     .sort((a, b) => (pageForShape(a, pages) - pageForShape(b, pages)) || (a.y - b.y))
-  const parts = shapes.filter((s) => s.kind === 'part')
+  // 'part' shapes carry the whole question tree: containers (isContainer) + leaf parts/subparts. They are the
+  // authoritative structure — the boundary-pair synthesis below is only a fallback for the manual workflow.
+  const structural = shapes.filter((s) => s.kind === 'part')
+  const containerShapes = structural.filter((s) => s.isContainer)
   const regions = shapes.filter((s) => s.kind !== 'boundary' && s.kind !== 'part')
 
   const questions: TemplateReplacePayload['questions'] = []
   const boundaries: TemplateReplacePayload['boundaries'] = []
   const bands: Array<{ questionId: string; top: ExamCanvasShapeModel; bottom: ExamCanvasShapeModel }> = []
 
+  // Stable question id per structural shape — prefer the persisted domain id so a re-save keeps join keys.
+  const idOf = new Map<string, string>()
+  for (const s of structural) idOf.set(s.id, isUuid(s.questionId) ? (s.questionId as string) : isUuid(s.id) ? s.id : newDomainId())
+  const emittedIds = new Set<string>(idOf.values())
+
+  // Boundary pairs: attach each pair to the container shape it spans (AI/structured path), else SYNTHESIZE a
+  // container question from the pair (pure manual authoring, no container box drawn). v1 always synthesized —
+  // which overwrote real containers and flattened the tree.
   for (let i = 0; i < orderedBoundaries.length; i += 2) {
     const top = orderedBoundaries[i]
     const bottom = orderedBoundaries[i + 1]
     if (!top || !bottom) break
-    const qNum = bands.length + 1
-    const questionId = isUuid(top.questionId) ? top.questionId : isUuid(bottom.questionId) ? bottom.questionId : newDomainId()
-    const label = top.label?.replace(/\s+(start|end)$/i, '') || bottom.label?.replace(/\s+(start|end)$/i, '') || `Q${qNum}`
-    questions.push({ id: questionId, label, order: qNum - 1, max_marks: 0, is_container: true, mark_scheme: {}, source: persistedSource(top), confirmed: persistedConfirmed(top), confidence: persistedConfidence(top), derivation: persistedDerivation(top) })
+    const label = top.label?.replace(/\s+(start|end)$/i, '') || bottom.label?.replace(/\s+(start|end)$/i, '') || `Q${bands.length + 1}`
+    // A container box whose vertical extent spans this start/end pair owns the boundary (structured path);
+    // otherwise the pair itself defines a container (manual path).
+    const pairTop = Math.min(top.y, bottom.y)
+    const pairBottom = Math.max(top.y, bottom.y)
+    const cover = containerShapes.find((c) => c.y <= pairTop + 4 && c.y + c.h >= pairBottom - 4)
+    let questionId: string
+    if (cover) {
+      questionId = idOf.get(cover.id) as string
+    } else {
+      questionId = isUuid(top.questionId) ? (top.questionId as string) : isUuid(bottom.questionId) ? (bottom.questionId as string) : newDomainId()
+      questions.push({ id: questionId, label, order: questions.length, max_marks: 0, is_container: true, mark_scheme: {}, source: persistedSource(top), confirmed: persistedConfirmed(top), confidence: persistedConfidence(top), derivation: persistedDerivation(top) })
+      emittedIds.add(questionId)
+    }
     bands.push({ questionId, top, bottom })
     for (const b of [top, bottom]) {
       boundaries.push({ id: isUuid(b.id) ? b.id : newDomainId(), question_id: questionId, label: b === top ? `${label} start` : `${label} end`, page_index: pageForShape(b, pages) - 1, y: b.y, bounds: boundaryBounds(b, pages), source: persistedSource(b), confirmed: persistedConfirmed(b), confidence: persistedConfidence(b), derivation: persistedDerivation(b) })
     }
   }
 
+  // Resolve a structural shape's parent: the persisted parent (if still emitted) wins — this is what keeps a
+  // 3-deep subpart→part→question chain intact across a save. Manually-drawn shapes with no persisted parent
+  // fall back to geometry: the deepest container box that contains them, else the boundary band around them.
+  const resolveParent = (s: ExamCanvasShapeModel): string | null => {
+    if (isUuid(s.parentId) && emittedIds.has(s.parentId as string)) return s.parentId as string
+    const containing = containerShapes
+      .filter((c) => c.id !== s.id && contains(bounds(c), bounds(s)))
+      .sort((a, b) => (b.depth ?? 0) - (a.depth ?? 0) || (a.w * a.h) - (b.w * b.h))
+    if (containing.length) return idOf.get(containing[0].id) ?? null
+    const band = bands.find((bd) => bandContains(bd.top, bd.bottom, s))
+    return band?.questionId ?? null
+  }
+
   const partQuestionIds = new Map<string, string>()
-  parts.sort((a, b) => (a.y - b.y) || (a.x - b.x)).forEach((part, index) => {
-    const parentBand = bands.find((band) => bandContains(band.top, band.bottom, part))
-    const qid = isUuid(part.questionId) ? part.questionId : isUuid(part.id) ? part.id : newDomainId()
+  const structuralSorted = [...structural].sort((a, b) => (a.depth ?? 0) - (b.depth ?? 0) || (a.y - b.y) || (a.x - b.x))
+  structuralSorted.forEach((part, index) => {
+    const qid = idOf.get(part.id) as string
     partQuestionIds.set(part.id, qid)
-    questions.push({ id: qid, parent_id: parentBand?.questionId ?? null, label: part.label || `Part ${index + 1}`, order: index, max_marks: Number(part.maxMarks ?? 0), answer_type: part.answerType ?? 'written', mcq_options: null, mark_scheme: {}, is_container: false, spec_ref: null, bounds: bounds(part), page: pageForShape(part, pages), source: persistedSource(part), confirmed: persistedConfirmed(part), confidence: persistedConfidence(part), derivation: persistedDerivation(part) })
+    questions.push({ id: qid, parent_id: resolveParent(part), label: part.label || (part.isContainer ? `Q${index + 1}` : `Part ${index + 1}`), order: index, max_marks: Number(part.maxMarks ?? 0), answer_type: part.isContainer ? null : (part.answerType ?? 'written'), mcq_options: null, mark_scheme: {}, is_container: !!part.isContainer, spec_ref: null, bounds: bounds(part), page: pageForShape(part, pages), source: persistedSource(part), confirmed: persistedConfirmed(part), confidence: persistedConfidence(part), derivation: persistedDerivation(part) })
   })
+  const parts = structural
 
   // Resolve each region's owner question. Order: current geometric containment (a user who drags a
   // region into a part re-attaches it) → the PERSISTED attachment if it still points at a saved
@@ -154,18 +199,29 @@ export function serializeCanvasShapes(template: ExamTemplateDetail, shapes: Exam
   // never silently drop a region while any question exists (only a template with zero questions can).
   const questionIds = new Set(questions.map((q) => q.id))
   const response_areas: TemplateReplacePayload['response_areas'] = []
+  // Prefer the DEEPEST (smallest) containing structural box so a region lands on its leaf part, not the
+  // enclosing container. Leaf parts win over containers at equal containment.
+  const deepestContainer = (region: ExamCanvasShapeModel): ExamCanvasShapeModel | undefined =>
+    parts
+      .filter((part) => part.id !== region.id && contains(bounds(part), bounds(region)))
+      .sort((a, b) => Number(!!a.isContainer) - Number(!!b.isContainer) || (a.w * a.h) - (b.w * b.h))[0]
   for (const region of regions) {
-    const containingPart = parts.find((part) => contains(bounds(part), bounds(region)))
+    const containingPart = deepestContainer(region)
     const persisted = isUuid(region.questionId) && questionIds.has(region.questionId) ? region.questionId : undefined
-    const nearestPart = parts.find((part) => pageForShape(part, pages) === pageForShape(region, pages)) ?? parts[0]
+    const nearestLeaf = parts.filter((p) => !p.isContainer).find((part) => pageForShape(part, pages) === pageForShape(region, pages)) ?? parts.find((p) => !p.isContainer) ?? parts[0]
     const questionId =
       (containingPart && partQuestionIds.get(containingPart.id))
       || persisted
-      || (nearestPart && partQuestionIds.get(nearestPart.id))
+      || (nearestLeaf && partQuestionIds.get(nearestLeaf.id))
       || questions[0]?.id
     if (!questionId) continue
     const kind = region.kind as ExamCanvasRegionKind
-    response_areas.push({ id: isUuid(region.id) ? region.id : newDomainId(), question_id: questionId, page: pageForShape(region, pages), bounds: bounds(region), kind, response_form: kind === 'response' ? (region.responseForm ?? 'lines') : null, context_type: kind === 'context' ? (region.contextType ?? 'generic') : null, source: persistedSource(region), confirmed: persistedConfirmed(region), confidence: persistedConfidence(region), mark_subtype: null, derivation: persistedDerivation(region) })
+    // Carry the figure/table name + caption through the save so a named context region survives a round-trip
+    // (the replace endpoint persists exam_response_areas.meta).
+    const meta = kind === 'context' && (region.label || region.description)
+      ? { name: region.label || undefined, description: region.description || undefined }
+      : undefined
+    response_areas.push({ id: isUuid(region.id) ? region.id : newDomainId(), question_id: questionId, page: pageForShape(region, pages), bounds: bounds(region), kind, response_form: kind === 'response' ? (region.responseForm ?? 'lines') : null, context_type: kind === 'context' ? (region.contextType ?? 'generic') : null, meta, source: persistedSource(region), confirmed: persistedConfirmed(region), confidence: persistedConfidence(region), mark_subtype: null, derivation: persistedDerivation(region) })
   }
 
   return { meta: { title: template.title, subject: template.subject ?? undefined, page_count: template.page_count ?? undefined, status: template.status }, questions, response_areas, boundaries, layout: template.layout ?? [] }
@@ -174,20 +230,35 @@ export function serializeCanvasShapes(template: ExamTemplateDetail, shapes: Exam
 export function shapesFromTemplate(detail: ExamTemplateDetail, pages?: CanvasPageGeometry[]): ExamCanvasShapeModel[] {
   const shapes: ExamCanvasShapeModel[] = []
   const questions = new Map(detail.questions.map((q) => [q.id, q]))
+  const depthOf = (id: string | null | undefined, guard = 0): number => {
+    const q = id ? questions.get(id) : undefined
+    return !q || !q.parent_id || guard > 8 ? 0 : 1 + depthOf(q.parent_id, guard + 1)
+  }
   for (const b of detail.boundaries ?? []) {
     const page = pageGeometry((b.page_index ?? 0) + 1, pages)
     // Boundary rows are y-lines. The old bounds rect is vestigial: keep y/domain ids,
     // but render and save a full rendered-page-width horizontal rule.
     shapes.push({ id: b.id, kind: 'boundary', x: page.x, y: Number(b.y), w: page.w, h: 8, label: b.label ?? undefined, questionId: b.question_id, source: b.source, confirmed: b.confirmed, confidence: b.confidence, derivation: b.derivation })
   }
+  // Draw the WHOLE tree that has geometry: containers (main questions / intermediate parts) AND leaf parts,
+  // each carrying its parent id + depth so nesting renders and a save preserves the N-deep chain. A question
+  // with no bounds still can't be drawn (legacy data) — it falls back to boundary-band synthesis on save.
   for (const q of detail.questions ?? []) {
-    if (q.is_container || !q.bounds) continue
-    shapes.push({ id: q.id, kind: 'part', x: Number(q.bounds.x ?? 80), y: Number(q.bounds.y ?? 120), w: Number(q.bounds.w ?? 420), h: Number(q.bounds.h ?? 180), label: q.label, maxMarks: q.max_marks, answerType: (q.answer_type as ExamCanvasShapeModel['answerType']) ?? 'written', questionId: q.id, source: q.source, confirmed: q.confirmed, confidence: q.confidence, derivation: q.derivation })
+    if (!q.bounds) continue
+    shapes.push({ id: q.id, kind: 'part', x: Number(q.bounds.x ?? 80), y: Number(q.bounds.y ?? 120), w: Number(q.bounds.w ?? 420), h: Number(q.bounds.h ?? 180), label: q.label, maxMarks: q.max_marks, answerType: q.is_container ? undefined : ((q.answer_type as ExamCanvasShapeModel['answerType']) ?? 'written'), questionId: q.id, parentId: q.parent_id, isContainer: q.is_container, depth: depthOf(q.id), source: q.source, confirmed: q.confirmed, confidence: q.confidence, derivation: q.derivation })
   }
   for (const r of detail.response_areas ?? []) {
     const bb = r.bounds ?? { x: 100, y: pageTop(r.page, pages) + 360, w: 360, h: 120 }
     const q = questions.get(r.question_id)
-    shapes.push({ id: r.id, kind: r.kind, x: Number(bb.x ?? 100), y: Number(bb.y ?? pageTop(r.page, pages) + 360), w: Number(bb.w ?? 360), h: Number(bb.h ?? 120), label: q ? `→ ${q.label}` : r.kind, responseForm: (r.response_form as ExamCanvasShapeModel['responseForm']) ?? undefined, contextType: r.context_type ?? undefined, questionId: r.question_id, source: r.source, confirmed: r.confirmed, confidence: r.confidence, derivation: r.derivation })
+    const meta = ((r as { meta?: Record<string, unknown> }).meta) ?? {}
+    const name = typeof meta.name === 'string' ? meta.name : undefined
+    const description = typeof meta.description === 'string' ? meta.description : undefined
+    // A context region is NAMED by its figure/table (was an anonymous purple box). Response/other regions keep
+    // the "→ owning question" label so their link is legible.
+    const label = r.kind === 'context'
+      ? (name || (r.context_type && r.context_type !== 'generic' ? r.context_type : 'Context'))
+      : (q ? `→ ${q.label}` : r.kind)
+    shapes.push({ id: r.id, kind: r.kind, x: Number(bb.x ?? 100), y: Number(bb.y ?? pageTop(r.page, pages) + 360), w: Number(bb.w ?? 360), h: Number(bb.h ?? 120), label, description, linkLabel: q?.label, responseForm: (r.response_form as ExamCanvasShapeModel['responseForm']) ?? undefined, contextType: r.context_type ?? undefined, questionId: r.question_id, source: r.source, confirmed: r.confirmed, confidence: r.confidence, derivation: r.derivation })
   }
   return addCheapReviewFlags(shapes, pages)
 }