README.md

@@ -44,6 +44,7 @@ The Builder can export a production-ready ZIP that contains:
 - site.webmanifest, robots.txt
 - Optional: sheets/ (Google Apps Script template)
 - Metadata files: assets.json, assets.index.json
+  - Integrity: assets.integrity.index.json
 
 ### Export Options UI
 
@@ -94,6 +95,17 @@ Simple index to quickly find assets by group:
 - fonts: string[] of zip paths
 - other: string[] of zip paths
 
+### assets.integrity.index.json
+
+- entries: array of `{ path, integrity }`
+  - `path`: asset `zipPath` (e.g. `assets/abcd1234.png` or grouped `assets/images/...`)
+  - `integrity`: `sha256-<base64>` (real SHA-256 of the asset bytes)
+- bundleHash: `sha256-<base64>` over a deterministic join of `path` and `integrity` for all entries
+
+Usage:
+- Verify file-level integrity by recomputing SHA-256(base64) of each asset and comparing with `entries[].integrity`.
+- Verify bundle integrity by recomputing `bundleHash` from sorted entries; useful for quick tamper detection.
+
 ### Google Sheets template (optional)
 
 - When included, ZIP contains:

components/BuilderClientPage.tsx

@@ -9,6 +9,7 @@ import { buildZip } from '@/lib/exporter/zip'
 import { buildExtrasForPage } from '@/lib/exporter/extras'
 import { buildAssetsMetadata } from '@/lib/exporter/assets.meta'
 import { buildAssetsIndex } from '@/lib/exporter/assets.index'
+import { buildAssetsIntegrityIndex } from '@/lib/exporter/assets.integrity.index'
 import type { Section } from '@/lib/state/store'
 import { createFormStore, type FormState } from '@/lib/state/formStore'
 import FormBuilderPanel from '@/components/FormBuilderPanel'
@@ -285,7 +286,11 @@ export default function BuilderClientPage() {
     const baseExtras = buildExtrasForPage(valid, { robotsText: robotsTextOverride, manifest: manifestOverride, sheetsMode })
     const extras: Record<string, Uint8Array> = {
       ...baseExtras,
-      ...(am ? { 'assets.json': buildAssetsMetadata(am), 'assets.index.json': buildAssetsIndex(am) } : {}),
+      ...(am ? {
+        'assets.json': buildAssetsMetadata(am),
+        'assets.index.json': buildAssetsIndex(am),
+        'assets.integrity.index.json': buildAssetsIntegrityIndex(am),
+      } : {}),
     }
     const zipBytes = await buildZip({ html: exported.html, css: exported.css, js: exported.js, assets, extras })
     download('landing.zip', zipBytes)

components/ExportOptions.ui.test.tsx

@@ -56,5 +56,7 @@ describe('Export Options UI → extras overrides', () => {
     expect(manifest.name).toBe(manifestName)
     expect(robotsRaw).toMatch(/Disallow: \/private/)
     expect(robotsRaw).toMatch(/Disallow: \/tmp/)
+    // integrity index should be included
+    expect(Object.prototype.hasOwnProperty.call(extras, 'assets.integrity.index.json')).toBe(true)
   })
 })

lib/exporter/assets.index.consistency.test.ts

@@ -0,0 +1,48 @@
+import { describe, it, expect } from 'vitest'
+import { AssetManager } from '@/lib/assets/assetManager'
+import { buildAssetsIndex } from '@/lib/exporter/assets.index'
+import { buildAssetsMetadata } from '@/lib/exporter/assets.meta'
+
+function u8(n: number): Uint8Array { const a = new Uint8Array(n); for (let i=0;i<n;i++) a[i]=i&0xff; return a }
+
+type IndexShape = { images: string[]; fonts: string[]; other: string[] }
+
+describe('assets.index.json ↔ assets.json consistency', () => {
+  it.each([
+    { mode: 'flat' as const },
+    { mode: 'grouped' as const },
+  ])('ensures index paths exist in assets.json zipPath with correct group ($mode)', async ({ mode }) => {
+    const am = new AssetManager({ maxBytes: 1024*1024, allowedExts: ['png','woff2','txt','jpg'], pathStrategy: mode })
+    await am.add({ name: 'hero.png', type: 'image/png', bytes: u8(10) })
+    await am.add({ name: 'thumb.jpg', type: 'image/jpeg', bytes: u8(11) })
+    await am.add({ name: 'main.woff2', type: 'font/woff2', bytes: u8(12) })
+    await am.add({ name: 'readme.txt', type: 'text/plain', bytes: u8(1) })
+
+    const indexBytes = buildAssetsIndex(am)
+    const metaBytes = buildAssetsMetadata(am)
+
+    const index = JSON.parse(new TextDecoder().decode(indexBytes)) as IndexShape
+    const meta = JSON.parse(new TextDecoder().decode(metaBytes)) as { assets: Array<{ zipPath: string; group: 'images'|'fonts'|'other' }> }
+
+    const metaByPath = new Map(meta.assets.map(a => [a.zipPath, a.group]))
+
+    for (const p of index.images) {
+      expect(metaByPath.has(p)).toBe(true)
+      expect(metaByPath.get(p)).toBe('images')
+    }
+    for (const p of index.fonts) {
+      expect(metaByPath.has(p)).toBe(true)
+      expect(metaByPath.get(p)).toBe('fonts')
+    }
+    for (const p of index.other) {
+      expect(metaByPath.has(p)).toBe(true)
+      expect(metaByPath.get(p)).toBe('other')
+    }
+
+    // Optional: ensure no extra paths exist in meta that are missing in index groups
+    const indexSet = new Set([...index.images, ...index.fonts, ...index.other])
+    for (const a of meta.assets) {
+      expect(indexSet.has(a.zipPath)).toBe(true)
+    }
+  })
+})

lib/exporter/assets.index.test.ts

@@ -19,4 +19,38 @@ describe('Assets index builder', () => {
     expect(obj.fonts[0]).toMatch(/^assets\/[0-9a-f]{8}\.woff2$/)
     expect(obj.other[0]).toMatch(/^assets\/[0-9a-f]{8}\.txt$/)
   })
+
+  it('sorts each group array by path (ascending)', async () => {
+    const am = new AssetManager({ maxBytes: 1024*1024, allowedExts: ['png','txt','woff2'] })
+    // Add in shuffled order so that sort is required
+    await am.add({ name: 'z.png', type: 'image/png', bytes: u8(3) })
+    await am.add({ name: 'a.png', type: 'image/png', bytes: u8(5) })
+    await am.add({ name: 'm.txt', type: 'text/plain', bytes: u8(2) })
+    await am.add({ name: 'b.txt', type: 'text/plain', bytes: u8(4) })
+    await am.add({ name: 'f.woff2', type: 'font/woff2', bytes: u8(6) })
+    await am.add({ name: 'e.woff2', type: 'font/woff2', bytes: u8(7) })
+    const bytes = buildAssetsIndex(am)
+    const obj = JSON.parse(new TextDecoder().decode(bytes)) as { images: string[]; fonts: string[]; other: string[] }
+    const imgs = [...obj.images]
+    const fonts = [...obj.fonts]
+    const others = [...obj.other]
+    const sortedImgs = [...imgs].sort()
+    const sortedFonts = [...fonts].sort()
+    const sortedOthers = [...others].sort()
+    expect(imgs).toEqual(sortedImgs)
+    expect(fonts).toEqual(sortedFonts)
+    expect(others).toEqual(sortedOthers)
+  })
+
+  it('respects grouped pathStrategy and outputs grouped paths in index', async () => {
+    const am = new AssetManager({ maxBytes: 1024*1024, allowedExts: ['png','woff2','txt'], pathStrategy: 'grouped' })
+    await am.add({ name: 'hero.png', type: 'image/png', bytes: u8(10) })
+    await am.add({ name: 'main.woff2', type: 'font/woff2', bytes: u8(12) })
+    await am.add({ name: 'readme.txt', type: 'text/plain', bytes: u8(1) })
+    const bytes = buildAssetsIndex(am)
+    const obj = JSON.parse(new TextDecoder().decode(bytes)) as { images: string[]; fonts: string[]; other: string[] }
+    expect(obj.images[0]).toMatch(/^assets\/images\/[0-9a-f]{8}\.png$/)
+    expect(obj.fonts[0]).toMatch(/^assets\/fonts\/[0-9a-f]{8}\.woff2$/)
+    expect(obj.other[0]).toMatch(/^assets\/other\/[0-9a-f]{8}\.txt$/)
+  })
 })

lib/exporter/assets.index.ts

@@ -7,6 +7,7 @@ export type AssetsIndex = {
 }
 
 export function buildAssetsIndex(am: AssetManager): Uint8Array {
+  // 그룹별 경로 수집
   const images: string[] = []
   const fonts: string[] = []
   const other: string[] = []
@@ -15,6 +16,10 @@ export function buildAssetsIndex(am: AssetManager): Uint8Array {
     else if (ref.mimeType.startsWith('font/')) fonts.push(ref.path)
     else other.push(ref.path)
   }
+  // 경로 사전순 정렬로 일정한 출력 보장
+  images.sort()
+  fonts.sort()
+  other.sort()
   const obj: AssetsIndex = { images, fonts, other }
   const json = JSON.stringify(obj, null, 2)
   return new TextEncoder().encode(json)

lib/exporter/assets.integrity.index.test.ts

@@ -0,0 +1,37 @@
+import { describe, it, expect } from 'vitest'
+import { AssetManager } from '@/lib/assets/assetManager'
+import { buildAssetsIntegrityIndex } from '@/lib/exporter/assets.integrity.index'
+import { buildAssetsMetadata } from '@/lib/exporter/assets.meta'
+
+function u8(n: number): Uint8Array { const a = new Uint8Array(n); for (let i=0;i<n;i++) a[i]=i&0xff; return a }
+
+describe('assets.integrity.index.json', () => {
+  it('emits path->integrity mapping consistent with assets.json and deterministically across modes and insertion order', async () => {
+    for (const mode of ['flat','grouped'] as const) {
+      // case1: insertion order A,B,C
+      const am1 = new AssetManager({ maxBytes: 1024*1024, allowedExts: ['png','woff2','txt'], pathStrategy: mode })
+      await am1.add({ name: 'a.png', type: 'image/png', bytes: u8(3) })
+      await am1.add({ name: 'b.woff2', type: 'font/woff2', bytes: u8(4) })
+      await am1.add({ name: 'c.txt', type: 'text/plain', bytes: u8(5) })
+      const idx1 = JSON.parse(new TextDecoder().decode(buildAssetsIntegrityIndex(am1))) as { entries: Array<{path:string; integrity:string}>; bundleHash: string }
+      const meta1 = JSON.parse(new TextDecoder().decode(buildAssetsMetadata(am1))) as { assets: Array<{ zipPath: string; integrity: string }> }
+      const metaMap1 = new Map(meta1.assets.map(a => [a.zipPath, a.integrity]))
+      const paths1 = idx1.entries.map(e => e.path)
+      const sorted1 = [...paths1].sort()
+      expect(paths1).toEqual(sorted1)
+      for (const e of idx1.entries) expect(metaMap1.get(e.path)).toBe(e.integrity)
+
+      // case2: insertion order shuffled C,A,B -> determinism of output
+      const am2 = new AssetManager({ maxBytes: 1024*1024, allowedExts: ['png','woff2','txt'], pathStrategy: mode })
+      await am2.add({ name: 'c.txt', type: 'text/plain', bytes: u8(5) })
+      await am2.add({ name: 'a.png', type: 'image/png', bytes: u8(3) })
+      await am2.add({ name: 'b.woff2', type: 'font/woff2', bytes: u8(4) })
+      const idx2 = JSON.parse(new TextDecoder().decode(buildAssetsIntegrityIndex(am2))) as { entries: Array<{path:string; integrity:string}>; bundleHash: string }
+      // same entries set and order (sorted by path) -> equality
+      expect(idx2.entries.map(e => e.path)).toEqual(idx1.entries.map(e => e.path))
+      expect(idx2.entries.map(e => e.integrity)).toEqual(idx1.entries.map(e => e.integrity))
+      // bundle hash depends on entries -> equal as well
+      expect(idx2.bundleHash).toBe(idx1.bundleHash)
+    }
+  })
+})

lib/exporter/assets.integrity.index.ts

@@ -0,0 +1,98 @@
+import type { AssetManager } from '@/lib/assets/assetManager'
+
+export type AssetsIntegrityIndex = {
+  entries: Array<{ path: string; integrity: string }>
+  bundleHash: string
+}
+
+// Minimal synchronous SHA-256 implementation returning base64 string.
+function sha256Base64(bytes: Uint8Array): string {
+  const K = new Uint32Array([
+    0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
+    0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
+    0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
+    0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
+    0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
+    0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
+    0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
+    0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
+  ])
+  const H = new Uint32Array([
+    0x6a09e667,0xbb67ae85,0x3c6ef372,0xa54ff53a,0x510e527f,0x9b05688c,0x1f83d9ab,0x5be0cd19
+  ])
+  const l = bytes.length
+  const bitLenHi = Math.floor((l >>> 29))
+  const bitLenLo = (l << 3) >>> 0
+  const withOne = l + 1
+  const padLen = ((withOne % 64) <= 56) ? (56 - (withOne % 64)) : (56 + 64 - (withOne % 64))
+  const totalLen = withOne + padLen + 8
+  const m = new Uint8Array(totalLen)
+  m.set(bytes)
+  m[l] = 0x80
+  m[totalLen - 8] = (bitLenHi >>> 24) & 0xff
+  m[totalLen - 7] = (bitLenHi >>> 16) & 0xff
+  m[totalLen - 6] = (bitLenHi >>> 8) & 0xff
+  m[totalLen - 5] = (bitLenHi >>> 0) & 0xff
+  m[totalLen - 4] = (bitLenLo >>> 24) & 0xff
+  m[totalLen - 3] = (bitLenLo >>> 16) & 0xff
+  m[totalLen - 2] = (bitLenLo >>> 8) & 0xff
+  m[totalLen - 1] = (bitLenLo >>> 0) & 0xff
+  const W = new Uint32Array(64)
+  for (let i = 0; i < totalLen; i += 64) {
+    for (let t = 0; t < 16; t++) {
+      const j = i + t * 4
+      W[t] = (m[j] << 24) | (m[j + 1] << 16) | (m[j + 2] << 8) | (m[j + 3])
+    }
+    for (let t = 16; t < 64; t++) {
+      const s0 = (rotr(W[t - 15], 7) ^ rotr(W[t - 15], 18) ^ (W[t - 15] >>> 3)) >>> 0
+      const s1 = (rotr(W[t - 2], 17) ^ rotr(W[t - 2], 19) ^ (W[t - 2] >>> 10)) >>> 0
+      W[t] = (W[t - 16] + s0 + W[t - 7] + s1) >>> 0
+    }
+    let a = H[0], b = H[1], c = H[2], d = H[3], e = H[4], f = H[5], g = H[6], h = H[7]
+    for (let t = 0; t < 64; t++) {
+      const S1 = (rotr(e, 6) ^ rotr(e, 11) ^ rotr(e, 25)) >>> 0
+      const ch = ((e & f) ^ (~e & g)) >>> 0
+      const temp1 = (h + S1 + ch + K[t] + W[t]) >>> 0
+      const S0 = (rotr(a, 2) ^ rotr(a, 13) ^ rotr(a, 22)) >>> 0
+      const maj = ((a & b) ^ (a & c) ^ (b & c)) >>> 0
+      const temp2 = (S0 + maj) >>> 0
+      h = g; g = f; f = e; e = (d + temp1) >>> 0; d = c; c = b; b = a; a = (temp1 + temp2) >>> 0
+    }
+    H[0] = (H[0] + a) >>> 0
+    H[1] = (H[1] + b) >>> 0
+    H[2] = (H[2] + c) >>> 0
+    H[3] = (H[3] + d) >>> 0
+    H[4] = (H[4] + e) >>> 0
+    H[5] = (H[5] + f) >>> 0
+    H[6] = (H[6] + g) >>> 0
+    H[7] = (H[7] + h) >>> 0
+  }
+  const out = new Uint8Array(32)
+  for (let i = 0; i < 8; i++) {
+    out[i*4+0]=(H[i]>>>24)&0xff; out[i*4+1]=(H[i]>>>16)&0xff; out[i*4+2]=(H[i]>>>8)&0xff; out[i*4+3]=(H[i]>>>0)&0xff
+  }
+  if (typeof Buffer !== 'undefined') return Buffer.from(out).toString('base64')
+  let s = ''; for (let i=0;i<out.length;i++) s += String.fromCharCode(out[i])
+  const btoaFn = (globalThis as unknown as { btoa?: (s: string) => string }).btoa
+  if (!btoaFn) throw new Error('btoa not available')
+  return btoaFn(s)
+  function rotr(x: number, n: number) { return (x >>> n) | (x << (32 - n)) }
+}
+
+export function buildAssetsIntegrityIndex(am: AssetManager): Uint8Array {
+  // 1) Collect entries: path + sha256 integrity
+  const entries = am.list().map(ref => ({
+    path: ref.path,
+    integrity: `sha256-${sha256Base64(ref.bytes)}`,
+  }))
+  // 2) Sort entries by path for deterministic output
+  entries.sort((a, b) => a.path.localeCompare(b.path))
+  // 3) Compute bundleHash over sorted lines: path + integrity joined by \n
+  const lines: string[] = []
+  for (const e of entries) { lines.push(e.path); lines.push(e.integrity) }
+  const joined = new TextEncoder().encode(lines.join('\n'))
+  const bundleHash = `sha256-${sha256Base64(joined)}`
+  const obj: AssetsIntegrityIndex = { entries, bundleHash }
+  const json = JSON.stringify(obj, null, 2)
+  return new TextEncoder().encode(json)
+}

lib/exporter/assets.integrity.sha256.test.ts

@@ -0,0 +1,31 @@
+import { describe, it, expect } from 'vitest'
+import { AssetManager } from '@/lib/assets/assetManager'
+import { buildAssetsMetadata, type AssetMetaItem } from '@/lib/exporter/assets.meta'
+import crypto from 'node:crypto'
+
+function u8pattern(n: number): Uint8Array {
+  const arr = new Uint8Array(n)
+  for (let i = 0; i < n; i++) arr[i] = (i * 131 + 7) & 0xff
+  return arr
+}
+
+function sha256B64(bytes: Uint8Array): string {
+  const h = crypto.createHash('sha256')
+  h.update(Buffer.from(bytes))
+  return h.digest('base64')
+}
+
+describe('assets.json integrity = real SHA-256(base64)', () => {
+  it('integrity equals sha256-<base64(sha256(bytes))>', async () => {
+    const am = new AssetManager({ maxBytes: 1024 * 1024, allowedExts: ['png'] })
+    const bytes = u8pattern(64)
+    await am.add({ name: 'hero.png', type: 'image/png', bytes })
+    const out = buildAssetsMetadata(am)
+    const json = new TextDecoder().decode(out)
+    const obj = JSON.parse(json) as { assets: AssetMetaItem[] }
+    expect(obj.assets.length).toBe(1)
+    const a = obj.assets[0]
+    const expected = 'sha256-' + sha256B64(bytes)
+    expect(a.integrity).toBe(expected)
+  })
+})

lib/exporter/assets.meta.ts

@@ -12,12 +12,106 @@ export type AssetMetaItem = {
   referencedAt: string[]
 }
 
+// Minimal synchronous SHA-256 implementation returning base64 string.
+// Derived from the SHA-256 specification. Suitable for small payloads (asset bytes).
+function sha256Base64(bytes: Uint8Array): string {
+  const K = new Uint32Array([
+    0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
+    0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
+    0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
+    0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
+    0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
+    0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
+    0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
+    0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
+  ])
+  const H = new Uint32Array([
+    0x6a09e667,0xbb67ae85,0x3c6ef372,0xa54ff53a,0x510e527f,0x9b05688c,0x1f83d9ab,0x5be0cd19
+  ])
+  const l = bytes.length
+  const bitLenHi = Math.floor((l >>> 29))
+  const bitLenLo = (l << 3) >>> 0
+  // Pre-processing (padding)
+  const withOne = l + 1
+  // pad to congruent 56 mod 64
+  const padLen = ((withOne % 64) <= 56) ? (56 - (withOne % 64)) : (56 + 64 - (withOne % 64))
+  const totalLen = withOne + padLen + 8
+  const m = new Uint8Array(totalLen)
+  m.set(bytes)
+  m[l] = 0x80
+  // append 64-bit big-endian length
+  m[totalLen - 8] = (bitLenHi >>> 24) & 0xff
+  m[totalLen - 7] = (bitLenHi >>> 16) & 0xff
+  m[totalLen - 6] = (bitLenHi >>> 8) & 0xff
+  m[totalLen - 5] = (bitLenHi >>> 0) & 0xff
+  m[totalLen - 4] = (bitLenLo >>> 24) & 0xff
+  m[totalLen - 3] = (bitLenLo >>> 16) & 0xff
+  m[totalLen - 2] = (bitLenLo >>> 8) & 0xff
+  m[totalLen - 1] = (bitLenLo >>> 0) & 0xff
+  const W = new Uint32Array(64)
+  for (let i = 0; i < totalLen; i += 64) {
+    for (let t = 0; t < 16; t++) {
+      const j = i + t * 4
+      W[t] = (m[j] << 24) | (m[j + 1] << 16) | (m[j + 2] << 8) | (m[j + 3])
+    }
+    for (let t = 16; t < 64; t++) {
+      const s0 = (rotr(W[t - 15], 7) ^ rotr(W[t - 15], 18) ^ (W[t - 15] >>> 3)) >>> 0
+      const s1 = (rotr(W[t - 2], 17) ^ rotr(W[t - 2], 19) ^ (W[t - 2] >>> 10)) >>> 0
+      W[t] = (W[t - 16] + s0 + W[t - 7] + s1) >>> 0
+    }
+    let a = H[0], b = H[1], c = H[2], d = H[3], e = H[4], f = H[5], g = H[6], h = H[7]
+    for (let t = 0; t < 64; t++) {
+      const S1 = (rotr(e, 6) ^ rotr(e, 11) ^ rotr(e, 25)) >>> 0
+      const ch = ((e & f) ^ (~e & g)) >>> 0
+      const temp1 = (h + S1 + ch + K[t] + W[t]) >>> 0
+      const S0 = (rotr(a, 2) ^ rotr(a, 13) ^ rotr(a, 22)) >>> 0
+      const maj = ((a & b) ^ (a & c) ^ (b & c)) >>> 0
+      const temp2 = (S0 + maj) >>> 0
+      h = g
+      g = f
+      f = e
+      e = (d + temp1) >>> 0
+      d = c
+      c = b
+      b = a
+      a = (temp1 + temp2) >>> 0
+    }
+    H[0] = (H[0] + a) >>> 0
+    H[1] = (H[1] + b) >>> 0
+    H[2] = (H[2] + c) >>> 0
+    H[3] = (H[3] + d) >>> 0
+    H[4] = (H[4] + e) >>> 0
+    H[5] = (H[5] + f) >>> 0
+    H[6] = (H[6] + g) >>> 0
+    H[7] = (H[7] + h) >>> 0
+  }
+  const out = new Uint8Array(32)
+  for (let i = 0; i < 8; i++) {
+    out[i * 4 + 0] = (H[i] >>> 24) & 0xff
+    out[i * 4 + 1] = (H[i] >>> 16) & 0xff
+    out[i * 4 + 2] = (H[i] >>> 8) & 0xff
+    out[i * 4 + 3] = (H[i] >>> 0) & 0xff
+  }
+  // base64 encode
+  let b64 = ''
+  if (typeof Buffer !== 'undefined') {
+    b64 = Buffer.from(out).toString('base64')
+  } else {
+    let s = ''
+    for (let i = 0; i < out.length; i++) s += String.fromCharCode(out[i])
+    // btoa is available in browsers
+    b64 = btoa(s)
+  }
+  return b64
+  function rotr(x: number, n: number) { return (x >>> n) | (x << (32 - n)) }
+}
+
 export function buildAssetsMetadata(am: AssetManager): Uint8Array {
   const list = am.list()
   const referenced = new Set(am.referencedList())
   const items: AssetMetaItem[] = list.map((ref) => {
-    // Browser-safe synchronous integrity: base64 of bytes as placeholder
+    // Compute real SHA-256(base64) integrity synchronously for browser/Node
-    const b64 = Buffer.from(ref.bytes).toString('base64')
+    const b64 = sha256Base64(ref.bytes)
     const group: 'images' | 'fonts' | 'other' = ref.mimeType.startsWith('image/')
       ? 'images'
       : ref.mimeType.startsWith('font/')

lib/exporter/assets.referenced.matrix.test.ts

@@ -0,0 +1,41 @@
+import { describe, it, expect } from 'vitest'
+import { AssetManager } from '@/lib/assets/assetManager'
+import { buildAssetsMetadata, type AssetMetaItem } from '@/lib/exporter/assets.meta'
+
+function u8(n: number): Uint8Array { const a = new Uint8Array(n); for (let i=0;i<n;i++) a[i]=i&0xff; return a }
+
+describe('referencedAt matrix across modes and multiple assets', () => {
+  it.each([
+    { mode: 'flat' as const },
+    { mode: 'grouped' as const },
+  ])('tracks only referenced originals once per asset ($mode)', async ({ mode }) => {
+    const am = new AssetManager({ maxBytes: 1024*1024, allowedExts: ['png','woff2'], pathStrategy: mode })
+    await am.add({ name: 'hero.png', type: 'image/png', bytes: u8(10) })
+    await am.add({ name: 'logo.png', type: 'image/png', bytes: u8(12) })
+    await am.add({ name: 'main.woff2', type: 'font/woff2', bytes: u8(14) })
+
+    // reference some assets multiple times; leave logo.png unreferenced
+    am.rewriteUrl('local:hero.png')
+    am.rewriteUrl('local:hero.png')
+    am.rewriteUrl('local:main.woff2')
+
+    const metaBytes = buildAssetsMetadata(am)
+    const obj = JSON.parse(new TextDecoder().decode(metaBytes)) as { assets: AssetMetaItem[] }
+    const byName = new Map(obj.assets.map(a => [a.originalName, a]))
+
+    const hero = byName.get('hero.png')!
+    const logo = byName.get('logo.png')!
+    const font = byName.get('main.woff2')!
+
+    expect(Array.isArray(hero.referencedAt)).toBe(true)
+    expect(hero.referencedAt).toContain('local:hero.png')
+    expect(hero.referencedAt.length).toBe(1)
+
+    expect(Array.isArray(font.referencedAt)).toBe(true)
+    expect(font.referencedAt).toContain('local:main.woff2')
+    expect(font.referencedAt.length).toBe(1)
+
+    expect(Array.isArray(logo.referencedAt)).toBe(true)
+    expect(logo.referencedAt.length).toBe(0)
+  })
+})

lib/exporter/assets.referenced.tracking.test.ts

@@ -0,0 +1,25 @@
+import { describe, it, expect } from 'vitest'
+import { AssetManager } from '@/lib/assets/assetManager'
+import { buildAssetsMetadata, type AssetMetaItem } from '@/lib/exporter/assets.meta'
+
+function u8(n: number): Uint8Array {
+  const arr = new Uint8Array(n)
+  for (let i = 0; i < n; i++) arr[i] = (i * 17) & 0xff
+  return arr
+}
+
+describe('referencedAt is populated when rewriteUrl is used', () => {
+  it('marks originalName as referenced via local:<name>', async () => {
+    const am = new AssetManager({ maxBytes: 1024 * 1024, allowedExts: ['png'] })
+    await am.add({ name: 'hero.png', type: 'image/png', bytes: u8(16) })
+    // use rewriteUrl to simulate page referencing the local asset
+    const rewritten = am.rewriteUrl('local:hero.png')
+    expect(rewritten).toMatch(/assets\//)
+    const metaBytes = buildAssetsMetadata(am)
+    const obj = JSON.parse(new TextDecoder().decode(metaBytes)) as { assets: AssetMetaItem[] }
+    expect(obj.assets.length).toBe(1)
+    const a = obj.assets[0]
+    expect(Array.isArray(a.referencedAt)).toBe(true)
+    expect(a.referencedAt).toContain('local:hero.png')
+  })
+})