perf(worksheets): use Suspense streaming for preview generation

Problem: The worksheet page had 1.7-2.3s TTFB because the 1.25MB SVG
preview was being serialized into the initial HTML response, blocking
first paint.

Solution: Use React Suspense to stream the preview separately:
- Page shell renders immediately with settings (~200ms TTFB)
- Preview generates async and streams in when ready (~1.5s later)
- User sees the UI instantly, preview appears with loading skeleton

New components:
- StreamedPreview: async server component that generates preview
- PreviewSkeleton: loading placeholder while streaming
- StreamedPreviewContext: shares streamed data with PreviewCenter
- PreviewDataInjector: bridges server-streamed data to client context

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude/settings.local.json

@@ -726,7 +726,11 @@
       "Bash(do curl -s -o /dev/null -w \"TTFB: %{time_starttransfer}s | Total: %{time_total}s\\\\n\" https://abaci.one/dashboard)",
       "Bash(do curl -s -o /dev/null -w \"TTFB: %{time_starttransfer}s | Total: %{time_total}s\\\\n\" https://abaci.one/tutorials)",
       "Bash(do curl -s -o /dev/null -w \"TTFB: %{time_starttransfer}s | Total: %{time_total}s\\\\n\" https://abaci.one/favicon.ico)",
-      "Bash(ping:*)"
+      "Bash(ping:*)",
+      "Bash(do echo \"=== $pod ===\")",
+      "Bash(do echo \"=== Request $i ===\")",
+      "Bash(while read -r line)",
+      "Bash(do echo $#ine)"
     ],
     "deny": [],
     "ask": []

apps/web/.claude/settings.local.json

@@ -119,7 +119,15 @@
       "mcp__chrome-devtools__get_network_request",
       "Bash(npm run db:push:*)",
       "Bash(kubectl get:*)",
-      "Bash(kubectl logs:*)"
+      "Bash(kubectl logs:*)",
+      "Bash(kubectl rollout:*)",
+      "Bash(kubectl describe:*)",
+      "Bash(docker pull:*)",
+      "Bash(helm show values:*)",
+      "WebFetch(domain:raw.githubusercontent.com)",
+      "Bash(helm get values:*)",
+      "Bash(kubectl set:*)",
+      "Bash(kubectl annotate:*)"
     ],
     "deny": [],
     "ask": []

apps/web/src/app/create/worksheets/components/AdditionWorksheetClient.tsx

@@ -3,7 +3,7 @@
 import { css } from '@styled/css'
 import { useSearchParams } from 'next/navigation'
 import { useTranslations } from 'next-intl'
-import { useEffect, useState } from 'react'
+import { useEffect, useState, type ReactNode } from 'react'
 import type { WorksheetFormState } from '@/app/create/worksheets/types'
 import { PageWithNav } from '@/components/PageWithNav'
 import { useTheme } from '@/contexts/ThemeContext'
@@ -15,16 +15,21 @@ import { ConfigSidebar } from './ConfigSidebar'
 import { GenerationErrorDisplay } from './GenerationErrorDisplay'
 import { PreviewCenter } from './PreviewCenter'
 import { ResponsivePanelLayout } from './ResponsivePanelLayout'
+import { StreamedPreviewProvider } from './StreamedPreviewContext'
 import { WorksheetConfigProvider } from './WorksheetConfigContext'
 
 interface AdditionWorksheetClientProps {
   initialSettings: Omit<WorksheetFormState, 'date' | 'rows' | 'total'>
+  /** @deprecated Use streamedPreview instead */
   initialPreview?: string[]
+  /** Suspense boundary containing the streaming preview */
+  streamedPreview?: ReactNode
 }
 
 export function AdditionWorksheetClient({
   initialSettings,
   initialPreview,
+  streamedPreview,
 }: AdditionWorksheetClientProps) {
   const searchParams = useSearchParams()
   const isFromShare = searchParams.get('from') === 'share'
@@ -79,7 +84,11 @@ export function AdditionWorksheetClient({
 
   return (
     <PageWithNav navTitle={t('navTitle')} navEmoji="📝">
+      <StreamedPreviewProvider>
         <WorksheetConfigProvider formState={formState} updateFormState={updateFormState}>
+          {/* Render the streamed preview Suspense boundary - it injects data into context */}
+          {streamedPreview}
+
           <div
             data-component="addition-worksheet-page"
             className={css({
@@ -109,6 +118,7 @@ export function AdditionWorksheetClient({
             <GenerationErrorDisplay error={error} visible={status === 'error'} onRetry={reset} />
           </div>
         </WorksheetConfigProvider>
+      </StreamedPreviewProvider>
     </PageWithNav>
   )
 }

apps/web/src/app/create/worksheets/components/PreviewCenter.tsx

@@ -12,6 +12,7 @@ import { extractConfigFields } from '../utils/extractConfigFields'
 import { FloatingPageIndicator } from './FloatingPageIndicator'
 import { LoadShareCodeModal } from './LoadShareCodeModal'
 import { ShareModal } from './ShareModal'
+import { useStreamedPreview } from './StreamedPreviewContext'
 import { useWorksheetConfig } from './WorksheetConfigContext'
 import { WorksheetPreview } from './WorksheetPreview'
 import { DuplicateWarningBanner } from './worksheet-preview/DuplicateWarningBanner'
@@ -39,8 +40,12 @@ export function PreviewCenter({
   const router = useRouter()
   const { resolvedTheme } = useTheme()
   const { onChange } = useWorksheetConfig()
+  const { streamedPages, isLoaded: isStreamedLoaded } = useStreamedPreview()
   const isDark = resolvedTheme === 'dark'
   const scrollContainerRef = useRef<HTMLDivElement>(null)
+
+  // Use streamed preview from context if available, otherwise fall back to prop
+  const effectivePreview = streamedPages ?? initialPreview
   const [isScrolling, setIsScrolling] = useState(false)
   const scrollTimeoutRef = useRef<NodeJS.Timeout>()
   const [isUploadModalOpen, setIsUploadModalOpen] = useState(false)
@@ -582,7 +587,7 @@ export function PreviewCenter({
       >
         <WorksheetPreview
           formState={formState}
-          initialData={initialPreview}
+          initialData={effectivePreview}
           isScrolling={isScrolling}
           onPageDataReady={setPageData}
         />

apps/web/src/app/create/worksheets/components/PreviewDataInjector.tsx

@@ -0,0 +1,31 @@
+'use client'
+
+import { useEffect } from 'react'
+import { useStreamedPreview } from './StreamedPreviewContext'
+
+interface PreviewDataInjectorProps {
+  pages?: string[]
+  totalPages?: number
+}
+
+/**
+ * Client component that receives streamed preview data from the server
+ * and injects it into the StreamedPreviewContext for use by PreviewCenter.
+ *
+ * This component renders nothing visible - it just bridges the server-streamed
+ * data into the client-side context system.
+ */
+export function PreviewDataInjector({ pages, totalPages }: PreviewDataInjectorProps) {
+  const { setStreamedPreview } = useStreamedPreview()
+
+  useEffect(() => {
+    console.log('[PreviewDataInjector] Received streamed preview:', {
+      pageCount: pages?.length ?? 0,
+      totalPages,
+    })
+    setStreamedPreview(pages, totalPages)
+  }, [pages, totalPages, setStreamedPreview])
+
+  // This component doesn't render anything visible
+  return null
+}

apps/web/src/app/create/worksheets/components/PreviewSkeleton.tsx

@@ -0,0 +1,85 @@
+'use client'
+
+import { css } from '@styled/css'
+
+/**
+ * Loading skeleton shown while the worksheet preview is being generated
+ * and streamed from the server.
+ */
+export function PreviewSkeleton() {
+  return (
+    <div
+      data-component="preview-skeleton"
+      className={css({
+        display: 'flex',
+        flexDirection: 'column',
+        alignItems: 'center',
+        justifyContent: 'center',
+        gap: '4',
+        padding: '8',
+        minHeight: '400px',
+      })}
+    >
+      {/* Worksheet page placeholder */}
+      <div
+        className={css({
+          width: '100%',
+          maxWidth: '600px',
+          aspectRatio: '11/8.5', // Letter landscape
+          backgroundColor: 'gray.200',
+          borderRadius: 'lg',
+          animation: 'pulse 2s ease-in-out infinite',
+          _dark: {
+            backgroundColor: 'gray.700',
+          },
+        })}
+      />
+
+      {/* Loading text */}
+      <div
+        className={css({
+          display: 'flex',
+          alignItems: 'center',
+          gap: '2',
+          color: 'gray.500',
+          fontSize: 'sm',
+          _dark: {
+            color: 'gray.400',
+          },
+        })}
+      >
+        <LoadingSpinner />
+        <span>Generating preview...</span>
+      </div>
+    </div>
+  )
+}
+
+function LoadingSpinner() {
+  return (
+    <svg
+      className={css({
+        width: '4',
+        height: '4',
+        animation: 'spin 1s linear infinite',
+      })}
+      xmlns="http://www.w3.org/2000/svg"
+      fill="none"
+      viewBox="0 0 24 24"
+    >
+      <circle
+        className={css({ opacity: 0.25 })}
+        cx="12"
+        cy="12"
+        r="10"
+        stroke="currentColor"
+        strokeWidth="4"
+      />
+      <path
+        className={css({ opacity: 0.75 })}
+        fill="currentColor"
+        d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z"
+      />
+    </svg>
+  )
+}

apps/web/src/app/create/worksheets/components/StreamedPreview.tsx

@@ -0,0 +1,37 @@
+import type { WorksheetFormState } from '@/app/create/worksheets/types'
+import { generateWorksheetPreview } from '../generatePreview'
+import { PreviewDataInjector } from './PreviewDataInjector'
+
+interface StreamedPreviewProps {
+  config: WorksheetFormState
+}
+
+/**
+ * Async server component that generates the worksheet preview.
+ * This runs inside a Suspense boundary, so it streams to the client
+ * when ready without blocking the initial page render.
+ */
+export async function StreamedPreview({ config }: StreamedPreviewProps) {
+  const startTime = Date.now()
+  console.log('[StreamedPreview] Starting preview generation...')
+
+  // Pre-generate first 3 pages (or fewer if config has fewer pages)
+  const INITIAL_PAGES = 3
+  const pagesToGenerate = Math.min(INITIAL_PAGES, config.pages ?? 1)
+
+  const previewResult = await generateWorksheetPreview(config, 0, pagesToGenerate - 1)
+
+  const elapsed = Date.now() - startTime
+  console.log(
+    `[StreamedPreview] Preview generation complete in ${elapsed}ms:`,
+    previewResult.success ? 'success' : 'failed'
+  )
+
+  // Return a client component that injects the preview data into context
+  return (
+    <PreviewDataInjector
+      pages={previewResult.success ? previewResult.pages : undefined}
+      totalPages={previewResult.totalPages}
+    />
+  )
+}

apps/web/src/app/create/worksheets/components/StreamedPreviewContext.tsx

@@ -0,0 +1,77 @@
+'use client'
+
+import { createContext, useContext, useState, useCallback, type ReactNode } from 'react'
+
+interface StreamedPreviewContextValue {
+  /**
+   * The streamed preview pages (SVG strings)
+   * undefined = not yet received, [] = received but empty/failed
+   */
+  streamedPages: string[] | undefined
+
+  /**
+   * Total number of pages in the worksheet (may be more than streamed pages)
+   */
+  totalPages: number | undefined
+
+  /**
+   * Whether the streamed preview has been received
+   */
+  isLoaded: boolean
+
+  /**
+   * Called by PreviewDataInjector when streamed data arrives
+   */
+  setStreamedPreview: (pages: string[] | undefined, totalPages: number | undefined) => void
+}
+
+const StreamedPreviewContext = createContext<StreamedPreviewContextValue | null>(null)
+
+interface StreamedPreviewProviderProps {
+  children: ReactNode
+}
+
+/**
+ * Provides streamed preview data to child components.
+ * The preview is generated server-side and streamed via Suspense,
+ * then injected into this context by PreviewDataInjector.
+ */
+export function StreamedPreviewProvider({ children }: StreamedPreviewProviderProps) {
+  const [streamedPages, setStreamedPages] = useState<string[] | undefined>(undefined)
+  const [totalPages, setTotalPages] = useState<number | undefined>(undefined)
+  const [isLoaded, setIsLoaded] = useState(false)
+
+  const setStreamedPreview = useCallback(
+    (pages: string[] | undefined, total: number | undefined) => {
+      setStreamedPages(pages)
+      setTotalPages(total)
+      setIsLoaded(true)
+    },
+    []
+  )
+
+  return (
+    <StreamedPreviewContext.Provider
+      value={{
+        streamedPages,
+        totalPages,
+        isLoaded,
+        setStreamedPreview,
+      }}
+    >
+      {children}
+    </StreamedPreviewContext.Provider>
+  )
+}
+
+/**
+ * Hook to access streamed preview data.
+ * Must be used within a StreamedPreviewProvider.
+ */
+export function useStreamedPreview(): StreamedPreviewContextValue {
+  const context = useContext(StreamedPreviewContext)
+  if (!context) {
+    throw new Error('useStreamedPreview must be used within StreamedPreviewProvider')
+  }
+  return context
+}

apps/web/src/app/create/worksheets/page.tsx

@@ -1,11 +1,13 @@
+import { Suspense } from 'react'
 import { eq, and } from 'drizzle-orm'
 import { db, schema } from '@/db'
 import { getViewerId } from '@/lib/viewer'
 import { parseAdditionConfig, defaultAdditionConfig } from '@/app/create/worksheets/config-schemas'
 import { AdditionWorksheetClient } from './components/AdditionWorksheetClient'
 import { WorksheetErrorBoundary } from './components/WorksheetErrorBoundary'
+import { PreviewSkeleton } from './components/PreviewSkeleton'
+import { StreamedPreview } from './components/StreamedPreview'
 import type { WorksheetFormState } from '@/app/create/worksheets/types'
-import { generateWorksheetPreview } from './generatePreview'
 
 /**
  * Get current date formatted as "Month Day, Year"
@@ -57,13 +59,6 @@ async function loadWorksheetSettings(): Promise<
     const savedSeed = (config as any).seed
     const finalSeed = savedSeed ?? Date.now() % 2147483647
 
-    console.log('[loadWorksheetSettings] Loaded from DB:', {
-      hasSavedSeed: !!savedSeed,
-      savedSeed,
-      finalSeed,
-      prngAlgorithm: (config as any).prngAlgorithm,
-    })
-
     return {
       ...config,
       seed: finalSeed,
@@ -80,48 +75,54 @@ async function loadWorksheetSettings(): Promise<
   }
 }
 
-export default async function AdditionWorksheetPage() {
-  const pageStart = Date.now()
-
-  console.log('[SSR] Starting worksheet page render...')
-  const settingsStart = Date.now()
-  const initialSettings = await loadWorksheetSettings()
-  console.log(`[SSR] loadWorksheetSettings: ${Date.now() - settingsStart}ms`)
-
-  // Calculate derived state needed for preview
-  // Use defaults for required fields (loadWorksheetSettings should always provide these, but TypeScript needs guarantees)
-  const problemsPerPage = initialSettings.problemsPerPage ?? 20
-  const pages = initialSettings.pages ?? 1
-  const cols = initialSettings.cols ?? 5
-
+/**
+ * Build full config from settings
+ */
+function buildFullConfig(
+  settings: Omit<WorksheetFormState, 'date' | 'rows' | 'total'>
+): WorksheetFormState {
+  const problemsPerPage = settings.problemsPerPage ?? 20
+  const pages = settings.pages ?? 1
+  const cols = settings.cols ?? 5
   const rows = Math.ceil((problemsPerPage * pages) / cols)
   const total = problemsPerPage * pages
 
-  // Create full config for preview generation
-  const fullConfig: WorksheetFormState = {
-    ...initialSettings,
+  return {
+    ...settings,
     rows,
     total,
     date: getDefaultDate(),
   }
+}
 
-  // Pre-generate ONLY the first 3 pages on the server
-  // The virtualization system will handle loading additional pages on-demand
-  const INITIAL_PAGES = 3
-  const pagesToGenerate = Math.min(INITIAL_PAGES, pages)
-  console.log(`[SSR] Generating initial ${pagesToGenerate} pages on server (total: ${pages})...`)
-  const previewStart = Date.now()
-  const previewResult = await generateWorksheetPreview(fullConfig, 0, pagesToGenerate - 1)
-  console.log(`[SSR] generateWorksheetPreview: ${Date.now() - previewStart}ms`)
-  console.log(`[SSR] Total page render: ${Date.now() - pageStart}ms`)
-  console.log('[SSR] Preview generation complete:', previewResult.success ? 'success' : 'failed')
+/**
+ * Worksheet page with Suspense streaming for preview
+ *
+ * Architecture:
+ * 1. Settings load fast (~50ms) - page shell renders immediately
+ * 2. Preview generates async (~500ms) and streams in via Suspense
+ * 3. User sees the page UI in ~200ms, preview appears when ready
+ */
+export default async function AdditionWorksheetPage() {
+  const pageStart = Date.now()
 
-  // Pass settings and preview to client, wrapped in error boundary
+  // Fast path: load settings from DB
+  const initialSettings = await loadWorksheetSettings()
+  console.log(`[SSR] Settings loaded in ${Date.now() - pageStart}ms`)
+
+  // Build full config for preview generation
+  const fullConfig = buildFullConfig(initialSettings)
+
+  // Page shell renders immediately, preview streams in via Suspense
   return (
     <WorksheetErrorBoundary>
       <AdditionWorksheetClient
         initialSettings={initialSettings}
-        initialPreview={previewResult.success ? previewResult.pages : undefined}
+        streamedPreview={
+          <Suspense fallback={<PreviewSkeleton />}>
+            <StreamedPreview config={fullConfig} />
+          </Suspense>
+        }
       />
     </WorksheetErrorBoundary>
   )