feat(exam): doc-view camera constraints and sidebar layout

Replaces infinite-canvas free-pan with a constrained vertical-scroll doc
view: tldraw setCameraOptions with behavior='contain', fit-x-100, and top
origin so the PDF never drifts side-to-side. Layout restructured from
floating overlays to flex column (top bar + sidebar/canvas row). Tool
panel is now a left sidebar, guide panel overlays canvas bottom-right.

PAGE_START_X changed from 260 → 0 so pages are flush left; camera
applyDocViewConstraints() called incrementally as pages stream in and
with resetZoom() once all pages are loaded.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pages/exam/setup/ExamTemplateSetupPage.tsx

@@ -29,7 +29,7 @@ const TOOLS = [
   { id: SHAPE_TYPES.furniture, label: 'Furniture', icon: canvasShapePalette.furniture.icon, tip: 'Mark page numbers, margins, blank space, or decoration to exclude from extraction.', color: 'inherit' as const },
 ]
 
-const PAGE_START_X = 260
+const PAGE_START_X = 0
 const PDF_PAGE_IDS_PREFIX = 'pdf-page-'
 
 function pageGeometryFromImages(pages: PdfPageImage[]): CanvasPageGeometry[] {
@@ -41,6 +41,22 @@ function pageGeometryFromImages(pages: PdfPageImage[]): CanvasPageGeometry[] {
   })
 }
 
+function applyDocViewConstraints(editor: Editor, pages: PdfPageImage[]) {
+  const maxW = pages.length ? Math.max(...pages.map((p) => p.width)) : PAGE_WIDTH
+  const totalH = pages.reduce((sum, p) => sum + p.height, 0) || PAGE_HEIGHT
+  editor.setCameraOptions({
+    constraints: {
+      bounds: { x: -64, y: -64, w: maxW + 128, h: totalH + 128 },
+      padding: { x: 64, y: 64 },
+      origin: { x: 0.5, y: 0 },
+      initialZoom: 'fit-x-100',
+      baseZoom: 'default',
+      behavior: 'contain',
+    },
+    isLocked: false,
+  })
+}
+
 function apiMessage(err: unknown): { message: string; conflict: boolean } {
   if (axios.isAxiosError(err)) {
     const detail = (err.response?.data as { detail?: string } | undefined)?.detail
@@ -176,6 +192,7 @@ const ExamTemplateSetupInner: React.FC = () => {
               ed.createShapes([{ id: shapeId, type: PDF_PAGE_SHAPE_TYPE, x: geometry.x, y: geometry.y, isLocked: true, props: { w: geometry.w, h: geometry.h, src: newPage.src, pageNumber: newPage.pageNumber } } as any])
               bringDomainShapesToFront(ed)
             }
+            applyDocViewConstraints(ed, partialPages)
           }
           setPdfStatus('ready')
         })
@@ -193,6 +210,8 @@ const ExamTemplateSetupInner: React.FC = () => {
         syncPdfPages(editor, pages)
         loadShapes(editor, shapesFromTemplate(detail, geometries))
         bringDomainShapesToFront(editor)
+        applyDocViewConstraints(editor, pages)
+        editor.resetZoom()
       }
       setDirty(false)
     } catch (e) {
@@ -248,25 +267,10 @@ const ExamTemplateSetupInner: React.FC = () => {
   )), [activeTool])
 
   return (
-    <Box sx={{ position: 'fixed', inset: 0, zIndex: (t) => t.zIndex.drawer + 20, bgcolor: 'background.default' }}>
-      <Box sx={{ position: 'absolute', inset: 0, '& .tlui-layout': { display: 'none' } }} data-testid="exam-template-setup-canvas">
-        <Tldraw
-          shapeUtils={examCanvasShapeUtils as any}
-          tools={examCanvasTools as any}
-          hideUi
-          inferDarkMode={theme.palette.mode === 'dark'}
-          autoFocus
-          onMount={(editor) => {
-            editorRef.current = editor
-            editor.user.updateUserPreferences({ colorScheme: theme.palette.mode === 'dark' ? 'dark' : 'light' })
-            editor.store.listen(() => setDirty(true), { scope: 'document' })
-            if (template) loadShapes(editor, shapesFromTemplate(template, pageGeometriesRef.current)); else seedGuide(editor)
-            bringDomainShapesToFront(editor)
-          }}
-        />
-      </Box>
+    <Box sx={{ position: 'fixed', inset: 0, zIndex: (t) => t.zIndex.drawer + 20, bgcolor: 'background.default', display: 'flex', flexDirection: 'column' }}>
 
-      <Paper elevation={8} sx={{ position: 'absolute', top: 12, left: 12, right: 12, px: 2, py: 1.25, display: 'flex', alignItems: 'center', gap: 1.5, borderRadius: 3, bgcolor: 'background.paper' }}>
+      {/* Top bar */}
+      <Paper elevation={8} sx={{ px: 2, py: 1.25, display: 'flex', alignItems: 'center', gap: 1.5, bgcolor: 'background.paper', borderRadius: 0, flexShrink: 0 }}>
         <Button startIcon={<ArrowBackIcon />} onClick={() => navigate('/exam-marker')} size="small">Back</Button>
         <Divider orientation="vertical" flexItem />
         <Box sx={{ minWidth: 0, flex: 1 }}>
@@ -277,32 +281,62 @@ const ExamTemplateSetupInner: React.FC = () => {
         <Button variant="contained" startIcon={saving ? <CircularProgress size={16} color="inherit" /> : <SaveIcon />} onClick={save} disabled={saving || loading || !template}>Save</Button>
       </Paper>
 
-      <Paper elevation={8} sx={{ position: 'absolute', top: 92, left: 12, p: 1.25, borderRadius: 3, bgcolor: 'background.paper' }}>
-        <Stack spacing={1}>{toolButtons}</Stack>
-      </Paper>
+      {/* Body row */}
+      <Box sx={{ flex: 1, display: 'flex', overflow: 'hidden' }}>
 
-      <Paper elevation={4} sx={{ position: 'absolute', right: 16, bottom: 16, maxWidth: 460, p: 2, borderRadius: 3, bgcolor: 'background.paper' }}>
-        <Typography variant="subtitle2" gutterBottom>Setup guide</Typography>
-        <Typography variant="body2" color="text.secondary" sx={{ mb: 1 }}>
-          1) Boundary start/end lines define each main question. 2) Draw amber Part boxes for markable sub-questions. 3) Draw coloured Response, Context, Q Number, Mark Area, Reference, and Furniture regions; Save derives parent links by containment.
-        </Typography>
-        <Stack direction="row" spacing={0.75} useFlexGap flexWrap="wrap" sx={{ my: 1 }}>
-          {(['boundary', 'part', 'response', 'context', 'question_number', 'mark_area', 'reference', 'furniture'] as const).map((kind) => {
-            const p = canvasShapePalette[kind]
-            return <Chip key={kind} size="small" label={`${p.icon} ${p.label}`} sx={{ borderColor: p.stroke, color: p.stroke, bgcolor: p.fill, fontWeight: 700 }} variant="outlined" />
-          })}
-        </Stack>
-        <Divider sx={{ my: 1 }} />
-        <Typography variant="caption" color="text.secondary" display="block">Multi-page boundary pairing</Typography>
-        <Typography variant="body2" sx={{ fontWeight: 700 }}>Draw “Q start” on page N, then “Q end” on a later page; save pairs boundaries by reading order into one question span.</Typography>
-        <Typography variant="caption" color="text.secondary" display="block" sx={{ mt: 0.75 }}>Open design choices resolved for v1: labels use “Q start/end”; persistent Attached pills confirm containment; rectangles stay simple for dense multi-column papers; Back button remains explicit.</Typography>
-        <Typography variant="caption" color={pdfStatus === 'ready' ? 'success.main' : pdfStatus === 'error' ? 'error.main' : 'text.secondary'} sx={{ display: 'block', mt: 1 }}>
-          PDF backdrop: {pdfStatus === 'ready' ? 'loaded and locked behind regions' : pdfStatus === 'loading' ? 'loading…' : pdfStatus === 'missing' ? 'no source PDF for this template' : pdfError ?? 'failed to load'}
-        </Typography>
-      </Paper>
+        {/* Left tool sidebar */}
+        <Paper elevation={4} sx={{ width: 160, flexShrink: 0, p: 1.25, borderRadius: 0, bgcolor: 'background.paper', overflowY: 'auto', display: 'flex', flexDirection: 'column', borderRight: 1, borderColor: 'divider' }}>
+          <Stack spacing={1}>{toolButtons}</Stack>
+        </Paper>
 
-      {loading && <Box sx={{ position: 'absolute', inset: 0, display: 'grid', placeItems: 'center', bgcolor: 'rgba(15,23,42,.18)' }}><CircularProgress /></Box>}
-      {conflict && <Alert severity="warning" sx={{ position: 'absolute', top: 86, right: 16, maxWidth: 560 }} onClose={() => setConflict(null)}>{conflict}</Alert>}
+        {/* Canvas area */}
+        <Box sx={{ flex: 1, position: 'relative', overflow: 'hidden' }} data-testid="exam-template-setup-canvas">
+          <Box sx={{ position: 'absolute', inset: 0, '& .tlui-layout': { display: 'none' } }}>
+            <Tldraw
+              shapeUtils={examCanvasShapeUtils as any}
+              tools={examCanvasTools as any}
+              hideUi
+              inferDarkMode={theme.palette.mode === 'dark'}
+              autoFocus
+              onMount={(editor) => {
+                editorRef.current = editor
+                editor.user.updateUserPreferences({ colorScheme: theme.palette.mode === 'dark' ? 'dark' : 'light' })
+                editor.store.listen(() => setDirty(true), { scope: 'document' })
+                applyDocViewConstraints(editor, [])
+                editor.resetZoom()
+                if (template) loadShapes(editor, shapesFromTemplate(template, pageGeometriesRef.current)); else seedGuide(editor)
+                bringDomainShapesToFront(editor)
+              }}
+            />
+          </Box>
+
+          {/* Guide panel */}
+          <Paper elevation={4} sx={{ position: 'absolute', right: 16, bottom: 16, maxWidth: 440, p: 2, borderRadius: 3, bgcolor: 'background.paper', zIndex: 1000 }}>
+            <Typography variant="subtitle2" gutterBottom>Setup guide</Typography>
+            <Typography variant="body2" color="text.secondary" sx={{ mb: 1 }}>
+              1) Boundary start/end lines define each main question. 2) Draw amber Part boxes for markable sub-questions. 3) Draw coloured Response, Context, Q Number, Mark Area, Reference, and Furniture regions; Save derives parent links by containment.
+            </Typography>
+            <Stack direction="row" spacing={0.75} useFlexGap flexWrap="wrap" sx={{ my: 1 }}>
+              {(['boundary', 'part', 'response', 'context', 'question_number', 'mark_area', 'reference', 'furniture'] as const).map((kind) => {
+                const p = canvasShapePalette[kind]
+                return <Chip key={kind} size="small" label={`${p.icon} ${p.label}`} sx={{ borderColor: p.stroke, color: p.stroke, bgcolor: p.fill, fontWeight: 700 }} variant="outlined" />
+              })}
+            </Stack>
+            <Divider sx={{ my: 1 }} />
+            <Typography variant="caption" color="text.secondary" display="block">Multi-page boundary pairing</Typography>
+            <Typography variant="body2" sx={{ fontWeight: 700 }}>Draw "Q start" on page N, then "Q end" on a later page; save pairs boundaries by reading order into one question span.</Typography>
+            <Typography variant="caption" color="text.secondary" display="block" sx={{ mt: 0.75 }}>Open design choices resolved for v1: labels use "Q start/end"; persistent Attached pills confirm containment; rectangles stay simple for dense multi-column papers; Back button remains explicit.</Typography>
+            <Typography variant="caption" color={pdfStatus === 'ready' ? 'success.main' : pdfStatus === 'error' ? 'error.main' : 'text.secondary'} sx={{ display: 'block', mt: 1 }}>
+              PDF backdrop: {pdfStatus === 'ready' ? 'loaded and locked behind regions' : pdfStatus === 'loading' ? 'loading…' : pdfStatus === 'missing' ? 'no source PDF for this template' : pdfError ?? 'failed to load'}
+            </Typography>
+          </Paper>
+
+          {/* Conflict alert */}
+          {conflict && <Alert severity="warning" sx={{ position: 'absolute', top: 16, right: 16, maxWidth: 560, zIndex: 1001 }} onClose={() => setConflict(null)}>{conflict}</Alert>}
+        </Box>
+      </Box>
+
+      {loading && <Box sx={{ position: 'absolute', inset: 0, display: 'grid', placeItems: 'center', bgcolor: 'rgba(15,23,42,.18)', zIndex: 10 }}><CircularProgress /></Box>}
       <Snackbar open={!!error} autoHideDuration={8000} onClose={() => setError(null)}><Alert severity="error" onClose={() => setError(null)}>{error}</Alert></Snackbar>
     </Box>
   )