feat(exam): render template PDFs behind setup canvas

src/utils/exam-canvas/model.test.ts

@@ -1,7 +1,6 @@
-
 import { describe, expect, it } from 'vitest'
 import type { ExamTemplateDetail } from '../../types/exam.types'
-import { isUuid, serializeCanvasShapes, shapesFromTemplate } from './model'
+import { isUuid, pageForY, serializeCanvasShapes, shapesFromTemplate } from './model'
 
 const template: ExamTemplateDetail = {
   id: 'tpl-1', title: 'Physics', subject: 'Physics', exam_id: null, exam_code: null, source_file_id: null, page_count: 1,
@@ -30,6 +29,23 @@ describe('exam setup canvas serialization', () => {
     expect(payload.boundaries.every((b) => isUuid(b.id))).toBe(true)
   })
 
+  it('maps shapes to the visible PDF page geometry rather than a fixed page height', () => {
+    const pages = [
+      { pageNumber: 1, x: 260, y: 0, w: 780, h: 1000 },
+      { pageNumber: 2, x: 260, y: 1000, w: 780, h: 1200 },
+    ]
+    expect(pageForY(1050, pages)).toBe(2)
+    const payload = serializeCanvasShapes(template, [
+      { id: 'b-top', kind: 'boundary', x: 260, y: 1020, w: 700, h: 8, label: 'Q1 start' },
+      { id: 'b-bottom', kind: 'boundary', x: 260, y: 1700, w: 700, h: 8, label: 'Q1 end' },
+      { id: 'part-1', kind: 'part', x: 300, y: 1120, w: 300, h: 160, label: 'Q1(a)' },
+      { id: 'resp-1', kind: 'response', x: 320, y: 1160, w: 240, h: 80 },
+    ], pages)
+    expect(payload.questions.find((q) => !q.is_container)?.page).toBe(2)
+    expect(payload.boundaries.every((b) => b.page_index === 1)).toBe(true)
+    expect(payload.response_areas[0].page).toBe(2)
+  })
+
   it('round-trips saved Part geometry and all S4-9 region kinds from API detail', () => {
     const shapes = shapesFromTemplate({
       ...template,