feat(chv): 阶段 4 截图三级管线——a11y 角色解析 + diff_shot 逐像素裁剪 + verify_shot 全屏校验

- snapshot 纯字符串解析 a11y 角色计数/interactive/字符数/hash
  （不跑 JS、不取原始 DOM，禁 op 保持拒绝）；status 带计数器
  与 verify_share
- diff_shot：PNG 全帧 Pillow 逐像素比对（单通道阈值 10），
  无变化 changed:false size 0；有变化 bbox 外扩 8px、钳制视口、
  宽高下限 32px，再 clip 截 JPEG q70；Pillow 缺失如实报错并
  指引回落 screenshot 全帧；open 不清基线（跨页局部差分靠它）
- verify_shot：全帧 JPEG q70，只用于检查点
- build.sh 与 playwright 同批 pip 装 pillow（只加 pillow）；
  buildinfo BASE_CONTENTS 登记 pillow（pip 名覆盖）
- 单测 cloud/tests/test_chv_opt_stage4.py：31 项（bbox 纯函数、
  a11y 解析、计数器、Pillow 缺失回落、禁 op、lockfile 往返）

chv-guest/build.sh

@@ -373,8 +373,11 @@ else
   echo "警告：cloud/chv/guest/vsock_notify.py 不在仓库里（P1 未合并），镜像暂不含 vsock notify" >&2
 fi
 if [ "${PLAYWRIGHT:-1}" = "1" ]; then
+  # 阶段 4：与 playwright 同批 pip 装 pillow（diff_shot 的逐像素
+  # 比对与 JPEG 编码用）。只加 pillow，不动其它包版本；BUILDINFO
+  # 的 pip freeze 会自然记录 pillow 版本，lockfile 按 pip 名覆盖。
   VC_ARGS+=(
-    --run-command '(pip3 install --no-cache-dir --break-system-packages playwright || pip3 install --no-cache-dir playwright) && PLAYWRIGHT_BROWSERS_PATH=/usr/local/share/ms-playwright python3 -m playwright install --with-deps chromium-headless-shell'
+    --run-command '(pip3 install --no-cache-dir --break-system-packages playwright pillow || pip3 install --no-cache-dir playwright pillow) && PLAYWRIGHT_BROWSERS_PATH=/usr/local/share/ms-playwright python3 -m playwright install --with-deps chromium-headless-shell'
     --run-command 'dpkg-query -W -f "\${Package} \${Version}\n" > /app/guest-versions-dpkg.txt; pip3 freeze > /app/guest-versions-pip.txt || true'
     --run-command 'ls /usr/local/share/ms-playwright/ > /app/guest-versions-chromium.txt 2>/dev/null || true')
 fi

chv-guest/buildinfo.py

@@ -46,6 +46,10 @@ BASE_CONTENTS = [
     # feat-chv-opt-landing（阶段 2）：cell veth 的 networkd
     # 不管配置（须排在 80-container-ve.network 之前）。
     "79-chv-cell.network",
+    # feat-chv-opt-landing（阶段 4）：Pillow（pip 包，diff_shot
+    # 逐像素比对与全帧 JPEG 编码用；只加 pillow，不动其它包版本。
+    # check/generate lockfile 按 pip 名覆盖，不走 DECLARED_SOURCES）。
+    "pillow",
 ]
 
 # 执行器默认内核 cmdline（config.py），构建产物须与它一起记录（B-12），

chv-guest/chv-browser.py

@@ -24,8 +24,32 @@
     executable_path，不走 channel/env）。
   * 截图：JPEG quality 70，viewport 宽封顶 1280（上下文创建时
     定死 1280x800）；diff_only 时与上一帧比对，字节相同即不落盘、
-    返回 changed=false（整帧相同跳过；变化区裁剪是阶段 4 的事，
+    返回 changed=false（整帧相同跳过）。
-    这里不冒充已做）。
+  * 阶段 4（feat-chv-opt-landing）：截图三级管线。
+    一级 a11y+DOM 主通道：snapshot 在 aria_snapshot 字符串基础
+    上纯字符串解析出角色计数（button/link/textbox/heading 等）
+    与 interactive 总数、a11y 字符数与 a11y_hash——不跑 JS、不取
+    原始 DOM、不新增 evaluate/content 通路，禁 op 保持拒绝。
+    二级差分截图（op `diff_shot`）：先截 PNG 全帧，用 Pillow
+    解码与上一帧逐像素比对——像素判变阈值 DIFF_PIXEL_THRESHOLD
+    =10（单通道差值 >10 才算变，滤掉抗锯齿 1 位抖动）；无变化
+    返回 changed:false size 0；有变化算出变化区 bbox（外扩
+    margin 8px、钳制到视口内、宽高下限 32px），再用
+    page.screenshot(type=jpeg, quality=70, clip=bbox) 只截变
+    化区。Pillow 缺失时 diff_shot 如实报错并指引回落全帧
+    screenshot，绝不静默假装裁剪。full_size 是本帧 PNG 经
+    Pillow 以 JPEG q70 编码得到的全帧字节数（与浏览器直出
+    JPEG q70 同参数、字节数可能有数百字节差异，仅作对照）。
+    三级全屏校验（op `verify_shot`）：全帧 JPEG q70，专用于
+    少数校验场景。事件驱动口径：日常只在动作后调 diff_shot
+    （变化才出图），verify_shot 只在检查点调用。计数器
+    shots_full/shots_diff/shots_verify/shots_skipped 由
+    status 返回，verify_share = shots_verify /
+    (shots_full+shots_diff+shots_verify)，分母为 0 时记 0.0。
+    计数口径：shots_full = screenshot 落盘数；shots_diff =
+    diff_shot 返回 changed:true 的数；shots_verify =
+    verify_shot 成功数；shots_skipped = screenshot diff_only
+    跳过数 + diff_shot changed:false 数。
 
 对齐 Muse P2 的不变口径：子代理只向单元返回页面无障碍快照，
 不见原始 DOM，不能在页面上下文跑 JS，不暴露 evaluate/content，
@@ -35,10 +59,19 @@ page.accessibility，改用 page.aria_snapshot()（返回 YAML 式
 
 操作（Unix socket /run/chv/browser.sock，JSON 行）：
   open       {url, session?} -> 导航并返回 {title, url, a11y, truncated}
-  snapshot   {session?}      -> 当前页的 {title, url, a11y, truncated}
+  snapshot   {session?}      -> 当前页的 {title, url, a11y, truncated,
+                                a11y_roles, a11y_interactive,
+                                a11y_chars, a11y_hash}
   screenshot {session?, diff_only?} -> JPEG 落盘 /run/chv/shots/<uuid>.jpg，
                                        返回 {path, size, format, quality,
                                              width, changed, sha256}
+  diff_shot  {session?}      -> PNG 全帧逐像素比对；无变化
+                                {changed:false, size:0}；有变化只截变
+                                化区 JPEG，返回 {changed:true, bbox,
+                                size, full_size, path, sha256}
+  verify_shot {session?}     -> 全帧 JPEG q70（只用于检查点），
+                                返回 {path, size, format, quality,
+                                      width, sha256}
   close      {session?}      -> 关该会话的页（浏览器进程继续跑）
   sessions   {}              -> 各会话 {session, url, title}
   status     {}              -> {engine, profile, profile_on_data_disk,
@@ -95,6 +128,20 @@ MAX_REQUEST_BYTES = 65536
 MAX_A11Y_NODES = 200
 MAX_A11Y_CHARS = 65536
 NAV_TIMEOUT_MS = 30000
+# 阶段 4 差分截图口径（写死在代码里，驱动与报告按此口径实测）：
+# 像素判变阈值：单通道差值 >10 才算变（滤抗锯齿 1 位抖动）；
+# bbox 外扩 margin 8px；变化区宽高下限 32px（不足则绕中心扩到
+# 32px 再钳制到视口内）。
+DIFF_PIXEL_THRESHOLD = 10
+DIFF_MARGIN_PX = 8
+DIFF_MIN_SIZE_PX = 32
+# a11y 角色里算 interactive 的集合（aria_snapshot 字符串解析用；
+# searchbox 是 textbox 的搜索变体，同样算可交互）。
+INTERACTIVE_ROLES = frozenset([
+    "button", "link", "textbox", "searchbox", "checkbox", "radio",
+    "combobox", "listbox", "menuitem", "tab", "switch", "slider",
+    "spinbutton",
+])
 
 # 拒绝的 URL 主机：localhost 与私有地址字面量（主机名判定）。
 _PRIVATE_HOST_RE = re.compile(
@@ -215,6 +262,137 @@ def truncate_a11y(node, max_nodes=MAX_A11Y_NODES,
     return tree, state["truncated"]
 
 
+def parse_a11y(a11y):
+    """解析无障碍快照出角色计数（纯函数，可单测）。
+
+    输入是 aria_snapshot 字符串（主路）或旧版 dict 树（回落）。
+    字符串按行解析：行形如 `- link "More information..." [ref=e3]`，
+    嵌套行带前导空格；角色取 `- ` 后的第一个 token。dict 树则
+    递归数每个节点的 role 字段。返回 (roles, interactive, chars,
+    a11y_hash)：roles 是 {角色: 个数}，interactive 是
+    INTERACTIVE_ROLES 内的角色总数，chars 是快照字符数，
+    a11y_hash 是快照规范文本的 sha256（字符串用原文，dict 用
+    sort_keys 的 JSON）。不跑 JS、不取原始 DOM。"""
+    roles = {}
+    if isinstance(a11y, str):
+        text = a11y
+        for line in text.splitlines():
+            m = re.match(r"^\s*-\s+([A-Za-z][\w-]*)", line)
+            if m:
+                role = m.group(1).lower()
+                roles[role] = roles.get(role, 0) + 1
+    elif isinstance(a11y, dict):
+        text = json.dumps(a11y, ensure_ascii=False, sort_keys=True)
+
+        def walk(n):
+            if not isinstance(n, dict):
+                return
+            role = n.get("role")
+            if isinstance(role, str) and role:
+                key = role.lower()
+                roles[key] = roles.get(key, 0) + 1
+            for value in n.values():
+                if isinstance(value, list):
+                    for child in value:
+                        walk(child)
+                elif isinstance(value, dict):
+                    walk(value)
+
+        walk(a11y)
+    else:
+        text = ""
+    interactive = sum(count for role, count in roles.items()
+                      if role in INTERACTIVE_ROLES)
+    digest = hashlib.sha256(text.encode()).hexdigest()
+    return roles, interactive, len(text), digest
+
+
+def expand_bbox(x0, y0, x1, y1, width, height,
+                margin=DIFF_MARGIN_PX, min_size=DIFF_MIN_SIZE_PX):
+    """变化区 bbox 外扩 + 钳制 + 最小尺寸（纯函数，可单测）。
+
+    输入是像素差分的包围盒（左闭右开 [x0,y0,x1,y1)）。先外扩
+    margin，再钳制到 [0,0,width,height] 内；宽/高不足 min_size
+    时绕中心扩到 min_size 再钳制（图本身比 min_size 还小时取
+    整幅宽/高）。返回 Playwright clip 形 {"x","y","width",
+    "height"}（均为 int）。"""
+    x0 = max(0, x0 - margin)
+    y0 = max(0, y0 - margin)
+    x1 = min(width, x1 + margin)
+    y1 = min(height, y1 + margin)
+    # 宽/高不足 min_size 时绕中心扩；一侧贴边扩不动时向另一侧
+    # 补足（只有图本身比 min_size 还窄/矮时才取整幅宽/高）。
+    for axis in ("x", "y"):
+        lo, hi, size = (x0, x1, width) if axis == "x" \
+            else (y0, y1, height)
+        if hi - lo < min_size:
+            need = min_size - (hi - lo)
+            lo = max(0, lo - need // 2)
+            hi = min(size, hi + (need - need // 2))
+            if hi - lo < min_size:
+                if lo == 0:
+                    hi = min(size, lo + min_size)
+                elif hi == size:
+                    lo = max(0, hi - min_size)
+            if hi - lo < min_size:
+                lo, hi = 0, size
+        if axis == "x":
+            x0, x1 = lo, hi
+        else:
+            y0, y1 = lo, hi
+    return {"x": int(x0), "y": int(y0),
+            "width": int(x1 - x0), "height": int(y1 - y0)}
+
+
+def _load_pillow():
+    """懒加载 Pillow（diff_shot 专用）；缺失时报明错并指引回落
+    全帧 screenshot，绝不静默假装裁剪。返回 (Image, ImageChops)。"""
+    try:
+        from PIL import Image, ImageChops
+    except ImportError as e:
+        raise RuntimeError(
+            "diff_shot 需要 Pillow（%s）：镜像里 pip 未装 pillow，"
+            "无法逐像素比对与裁剪；回落：用 screenshot 全帧 JPEG "
+            "q70（op screenshot，不带 diff_only）" % e)
+    return Image, ImageChops
+
+
+def compute_diff_bbox(prev_png, cur_png,
+                      margin=DIFF_MARGIN_PX,
+                      min_size=DIFF_MIN_SIZE_PX,
+                      pillow=None):
+    """两帧 PNG 的逐像素比对（纯函数，可单测，需 Pillow）。
+
+    返回 (changed, bbox)：无变化时 (False, None)；有变化时
+    (True, clip dict)。像素判变：逐通道差值 > DIFF_PIXEL_THRESHOLD
+    才算变（见模块 docstring）。两帧尺寸不同时视为整帧变化，
+    bbox 即当前帧全幅。pillow 供单测注入 (Image, ImageChops)，
+    正常运行时用 _load_pillow()。"""
+    Image, ImageChops = pillow or _load_pillow()
+    import io
+    prev = Image.open(io.BytesIO(prev_png)).convert("RGB")
+    cur = Image.open(io.BytesIO(cur_png)).convert("RGB")
+    width, height = cur.size
+    if prev.size != cur.size:
+        return True, {"x": 0, "y": 0, "width": width,
+                      "height": height}
+    diff = ImageChops.difference(prev, cur)
+    # 逐通道阈值掩码：任一通道差值 >10 即变（convert("L") 会按
+    # 亮度加权、漏掉单通道小变化，故三通道分别取阈值再取并）。
+    masks = []
+    for channel in diff.split():
+        masks.append(channel.point(
+            lambda p: 255 if p > DIFF_PIXEL_THRESHOLD else 0))
+    mask = masks[0]
+    for extra in masks[1:]:
+        mask = ImageChops.lighter(mask, extra)
+    box = mask.getbbox()
+    if box is None:
+        return False, None
+    return True, expand_bbox(box[0], box[1], box[2], box[3],
+                             width, height, margin, min_size)
+
+
 def _load_playwright():
     """懒加载 playwright；缺失时报明错（不静默假装有浏览器）。
     返回 sync_playwright() 的上下文管理器实例（须调用，
@@ -278,6 +456,10 @@ class BrowserAgent:
         self._engine = "shell"
         self._mounted_full = False
         self._last_shot = {}
+        # 阶段 4：上一帧 PNG（diff_shot 的比对基线）与截图计数器。
+        self._last_png = {}
+        self._counters = {"shots_full": 0, "shots_diff": 0,
+                          "shots_verify": 0, "shots_skipped": 0}
 
     # -- 浏览器生命周期 ----------------------------------------------
     def _close_context(self):
@@ -394,6 +576,11 @@ class BrowserAgent:
                     pass
             page = self._context.new_page()
             self._pages[session] = page
+            # 注意：open 不清 diff 基线——diff_shot 永远与“上一帧”
+            # 逐像素比对，不管上一帧是哪一页；导航后调 diff_shot
+            # 得到的正是新旧两页渲染的真实差异区（跨页局部变化
+            # 如搜索词 Cat->Dog 就靠这个）。只有 close（会话结束）
+            # 才清基线，下次 open 后的首次 diff_shot 为全幅首帧。
             page.goto(url, timeout=NAV_TIMEOUT_MS)
             page.wait_for_load_state("domcontentloaded",
                                      timeout=NAV_TIMEOUT_MS)
@@ -431,8 +618,12 @@ class BrowserAgent:
                                  "aria_snapshot/accessibility）"}
         except Exception as e:
             return {"ok": False, "error": "取快照失败：%s" % e}
+        # 阶段 4 一级通道：纯字符串解析 enrich（不跑 JS、不取 DOM）。
+        roles, interactive, chars, digest = parse_a11y(tree)
         return {"ok": True, "title": title, "url": url,
                 "a11y": tree, "truncated": truncated,
+                "a11y_roles": roles, "a11y_interactive": interactive,
+                "a11y_chars": chars, "a11y_hash": digest,
                 "session": session}
 
     def screenshot(self, session=None, diff_only=False):
@@ -453,7 +644,8 @@ class BrowserAgent:
         digest = hashlib.sha256(data).hexdigest()
         if diff_only and self._last_shot.get(session) == digest:
             # 整帧与上一帧字节相同：跳过落盘（阶段 4 的变化区
-            # 裁剪不在本阶段做，这里只做整帧相同跳过）。
+            # 裁剪走 diff_shot op，这里只做整帧相同跳过）。
+            self._counters["shots_skipped"] += 1
             return {"ok": True, "changed": False, "size": 0,
                     "path": None, "format": "jpeg",
                     "quality": JPEG_QUALITY,
@@ -467,11 +659,124 @@ class BrowserAgent:
         except OSError as e:
             return {"ok": False, "error": "截图落盘失败：%s" % e}
         self._last_shot[session] = digest
+        self._counters["shots_full"] += 1
         return {"ok": True, "path": path, "size": len(data),
                 "format": "jpeg", "quality": JPEG_QUALITY,
                 "width": VIEWPORT_WIDTH, "changed": True,
                 "sha256": digest, "session": session}
 
+    def diff_shot(self, session=None):
+        """二级差分截图（阶段 4）：PNG 全帧逐像素比对，只截变化区。
+
+        无变化：{changed:false, size:0}（计 shots_skipped）。
+        有变化：clip=bbox 的 JPEG q70 落盘，返回 {changed:true,
+        bbox, size, full_size, path, sha256}（计 shots_diff）。
+        首帧（本会话无上一帧）视为整帧变化，bbox 为全视口。
+        Pillow 缺失时 ok:false 并指引回落 screenshot 全帧，
+        不计入计数器、不落盘、不假装裁剪。"""
+        session = session or DEFAULT_SESSION
+        page = self._page(session)
+        if page is None:
+            return {"ok": False,
+                    "error": "会话 %s 还没有打开的页面（先 open）"
+                             % session}
+        try:
+            png = page.screenshot(type="png")
+        except Exception as e:
+            return {"ok": False, "error": "截图失败：%s" % e}
+        if not isinstance(png, (bytes, bytearray)):
+            return {"ok": False, "error": "截图未返回字节数据"}
+        png = bytes(png)
+        try:
+            Image, _ImageChops = _load_pillow()
+        except RuntimeError as e:
+            return {"ok": False, "error": str(e),
+                    "fallback": "screenshot"}
+        prev = self._last_png.get(session)
+        if prev is None:
+            changed, bbox = True, {"x": 0, "y": 0,
+                                   "width": VIEWPORT_WIDTH,
+                                   "height": VIEWPORT_HEIGHT}
+        else:
+            try:
+                changed, bbox = compute_diff_bbox(prev, png)
+            except Exception as e:
+                return {"ok": False,
+                        "error": "差分比对失败：%s" % e}
+        # full_size：本帧 PNG 经 Pillow 以 JPEG q70 编码的全帧
+        # 字节数（与浏览器直出同参数，仅作对照，不直接等同）。
+        import io
+        try:
+            buf = io.BytesIO()
+            Image.open(io.BytesIO(png)).convert("RGB").save(
+                buf, "JPEG", quality=JPEG_QUALITY)
+            full_size = len(buf.getvalue())
+        except Exception:
+            full_size = len(png)
+        self._last_png[session] = png
+        if not changed:
+            self._counters["shots_skipped"] += 1
+            return {"ok": True, "changed": False, "size": 0,
+                    "path": None, "bbox": None,
+                    "full_size": full_size, "format": "jpeg",
+                    "quality": JPEG_QUALITY, "session": session}
+        try:
+            clip = page.screenshot(type="jpeg",
+                                   quality=JPEG_QUALITY, clip=bbox)
+        except Exception as e:
+            return {"ok": False, "error": "变化区截图失败：%s" % e}
+        if not isinstance(clip, (bytes, bytearray)):
+            return {"ok": False, "error": "变化区截图未返回字节数据"}
+        clip = bytes(clip)
+        try:
+            os.makedirs(self._shots_dir, exist_ok=True)
+            path = os.path.join(self._shots_dir, "%s.jpg"
+                                % uuid.uuid4().hex)
+            with open(path, "wb") as fh:
+                fh.write(clip)
+        except OSError as e:
+            return {"ok": False, "error": "截图落盘失败：%s" % e}
+        self._counters["shots_diff"] += 1
+        return {"ok": True, "changed": True, "bbox": bbox,
+                "path": path, "size": len(clip),
+                "full_size": full_size, "format": "jpeg",
+                "quality": JPEG_QUALITY,
+                "sha256": hashlib.sha256(clip).hexdigest(),
+                "session": session}
+
+    def verify_shot(self, session=None):
+        """三级全屏校验（阶段 4）：全帧 JPEG q70，只用于检查点。
+        计 shots_verify。日常动作后用 diff_shot，检查点才调它。"""
+        session = session or DEFAULT_SESSION
+        page = self._page(session)
+        if page is None:
+            return {"ok": False,
+                    "error": "会话 %s 还没有打开的页面（先 open）"
+                             % session}
+        try:
+            data = page.screenshot(type="jpeg",
+                                   quality=JPEG_QUALITY)
+        except Exception as e:
+            return {"ok": False, "error": "截图失败：%s" % e}
+        if not isinstance(data, (bytes, bytearray)):
+            return {"ok": False, "error": "截图未返回字节数据"}
+        data = bytes(data)
+        try:
+            os.makedirs(self._shots_dir, exist_ok=True)
+            path = os.path.join(self._shots_dir, "%s.jpg"
+                                % uuid.uuid4().hex)
+            with open(path, "wb") as fh:
+                fh.write(data)
+        except OSError as e:
+            return {"ok": False, "error": "截图落盘失败：%s" % e}
+        self._last_shot[session] = hashlib.sha256(data).hexdigest()
+        self._counters["shots_verify"] += 1
+        return {"ok": True, "path": path, "size": len(data),
+                "format": "jpeg", "quality": JPEG_QUALITY,
+                "width": VIEWPORT_WIDTH, "changed": True,
+                "sha256": self._last_shot[session],
+                "session": session}
+
     def close(self, session=None):
         session = session or DEFAULT_SESSION
         page = self._pages.pop(session, None)
@@ -481,6 +786,7 @@ class BrowserAgent:
             except Exception:
                 pass
         self._last_shot.pop(session, None)
+        self._last_png.pop(session, None)
         return {"ok": True, "closed": True, "session": session}
 
     def sessions(self):
@@ -499,6 +805,11 @@ class BrowserAgent:
 
     # -- 服务化：状态 / CDP / 引擎 --------------------------------------
     def status(self):
+        total = (self._counters["shots_full"]
+                 + self._counters["shots_diff"]
+                 + self._counters["shots_verify"])
+        verify_share = (self._counters["shots_verify"] / total
+                        if total else 0.0)
         return {"ok": True, "engine": self._engine,
                 "profile": self._profile_dir,
                 "profile_on_data_disk": self._profile_on_data_disk,
@@ -509,7 +820,9 @@ class BrowserAgent:
                 "mounted_full": self._mounted_full,
                 "full_present": full_chromium_present(
                     self._full_browsers_dir),
-                "full_browsers_dir": self._full_browsers_dir}
+                "full_browsers_dir": self._full_browsers_dir,
+                "counters": dict(self._counters),
+                "verify_share": verify_share}
 
     def cdp(self):
         ok, err = self._ensure_browser()
@@ -607,6 +920,10 @@ def handle_request(agent, req):
     if op == "screenshot":
         return agent.screenshot(req.get("session"),
                                 bool(req.get("diff_only")))
+    if op == "diff_shot":
+        return agent.diff_shot(req.get("session"))
+    if op == "verify_shot":
+        return agent.verify_shot(req.get("session"))
     if op == "close":
         return agent.close(req.get("session"))
     if op == "sessions":
@@ -623,6 +940,7 @@ def handle_request(agent, req):
         return agent.unmount_full()
     return {"ok": False,
             "error": "未知操作：%r（白名单：open/snapshot/screenshot/"
+                     "diff_shot/verify_shot/"
                      "close/sessions/status/cdp/engine/mount_full/"
                      "unmount_full/ping）" % (op,)}
 

cloud/tests/test_chv_opt_stage4.py

@@ -0,0 +1,562 @@
+"""阶段 4（截图三级管线）测试：a11y 角色解析 + 差分截图 bbox +
+全屏校验 + 计数器 + Pillow 缺失回落 + 禁 op 仍拒绝 + build 接线。
+
+只测本轨交付物（chv-guest/chv-browser.py、build.sh、
+buildinfo.py、check/generate_lockfile.py）。全部用假
+playwright/假 PNG（标准库 zlib 编码）/假文件系统，绝不连真实
+网络、不起真实 VM。Pillow 正向路径用本机已装的 Pillow 跑；
+缺失路径用注入的 _load_pillow 假失败覆盖。
+"""
+import hashlib
+import importlib.util
+import json
+import os
+import struct
+import subprocess
+import sys
+import tempfile
+import unittest
+import zlib
+from pathlib import Path
+from unittest import mock
+
+ROOT = Path(__file__).resolve().parents[2]
+
+
+def _load_script(name):
+    path = ROOT / "chv-guest" / name
+    spec = importlib.util.spec_from_file_location(
+        "chv_guest_s4_" + name[:-3], str(path))
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module
+
+
+BROWSER = _load_script("chv-browser.py")
+BUILDINFO = _load_script("buildinfo.py")
+CHECK = _load_script("check_lockfile.py")
+GENERATE = _load_script("generate_lockfile.py")
+
+
+def encode_png(width, height, pixels):
+    """标准库编码 RGB PNG：pixels 是 {(x, y): (r, g, b)}，缺省白。
+    供 compute_diff_bbox / diff_shot 的假帧用（不依赖 Pillow 编码）。"""
+    def chunk(kind, data):
+        out = struct.pack(">I", len(data)) + kind + data
+        return out + struct.pack(">I", zlib.crc32(kind + data) & 0xFFFFFFFF)
+
+    ihdr = struct.pack(">IIBBBBB", width, height, 8, 2, 0, 0, 0)
+    raw = bytearray()
+    for y in range(height):
+        raw.append(0)
+        for x in range(width):
+            raw.extend(pixels.get((x, y), (255, 255, 255)))
+    return (b"\x89PNG\r\n\x1a\n" + chunk(b"IHDR", ihdr)
+            + chunk(b"IDAT", zlib.compress(bytes(raw)))
+            + chunk(b"IEND", b""))
+
+
+def solid_png(width, height, color=(255, 255, 255)):
+    return encode_png(width, height, {
+        (x, y): color for x in range(width) for y in range(height)})
+
+
+ARIA_SAMPLE = """- generic [ref=e1]:
+  - heading "Example Domain" [level=1]
+  - paragraph "This domain is for use in illustrative examples"
+  - link "More information..." [ref=e3]
+  - button "Search" [ref=e4]
+  - textbox "Keywords" [ref=e5]
+  - searchbox "Site search" [ref=e6]
+  - checkbox "Remember me" [checked]
+  - heading "Second heading" [level=2]
+"""
+
+
+class FakePage:
+    def __init__(self, title="Example Domain", aria=None):
+        self.url = "about:blank"
+        self._title = title
+        self._aria = aria if aria is not None else ARIA_SAMPLE
+        self._frame = solid_png(64, 48)
+        self.shots = []
+
+    def set_frame(self, png_bytes):
+        self._frame = png_bytes
+
+    def goto(self, url, timeout=None):
+        self.url = url.rstrip("/") + "/"
+
+    def wait_for_load_state(self, state, timeout=None):
+        pass
+
+    def title(self):
+        return self._title
+
+    def aria_snapshot(self):
+        return self._aria
+
+    def screenshot(self, path=None, type=None, quality=None, clip=None):
+        self.shots.append((type, quality, clip))
+        if type == "png":
+            return self._frame
+        if clip is not None:
+            return (b"\xff\xd8CLIP-%d-%d-%d-%d"
+                    % (clip["x"], clip["y"], clip["width"],
+                       clip["height"]))
+        assert type == "jpeg", type
+        assert quality == 70, quality
+        return b"\xff\xd8\xff\xe0FAKEJPEG-" + self._title.encode()
+
+    def close(self):
+        pass
+
+
+class FakeContext:
+    def __init__(self, pages):
+        self._pages = list(pages)
+        self._idx = 0
+        self.launches = []
+
+    def new_page(self):
+        page = self._pages[self._idx % len(self._pages)]
+        self._idx += 1
+        return page
+
+    def close(self):
+        pass
+
+
+class FakeEntered:
+    def __init__(self, context):
+        self.chromium = mock.Mock()
+        self._context = context
+        self.calls = []
+
+        def launch_persistent(user_data_dir, **kwargs):
+            self.calls.append((user_data_dir, kwargs))
+            return context
+
+        self.chromium.launch_persistent_context.side_effect = \
+            launch_persistent
+
+
+def _agent(pages, tmp):
+    ctx = FakeContext(pages)
+    holder = {}
+
+    class PW:
+        def __enter__(self):
+            entered = FakeEntered(ctx)
+            holder["entered"] = entered
+            return entered
+
+        def __exit__(self, *exc):
+            return False
+
+    agent = BROWSER.BrowserAgent(
+        playwright_factory=lambda: PW(), shots_dir=tmp,
+        profile_dir=os.path.join(tmp, "profile"))
+    return agent, ctx, holder
+
+
+class ParseA11yTest(unittest.TestCase):
+    def test_counts_roles_and_interactive(self):
+        roles, interactive, chars, digest = BROWSER.parse_a11y(
+            ARIA_SAMPLE)
+        self.assertEqual(roles.get("heading"), 2)
+        self.assertEqual(roles.get("link"), 1)
+        self.assertEqual(roles.get("button"), 1)
+        self.assertEqual(roles.get("textbox"), 1)
+        self.assertEqual(roles.get("searchbox"), 1)
+        self.assertEqual(roles.get("checkbox"), 1)
+        self.assertEqual(roles.get("paragraph"), 1)
+        self.assertEqual(roles.get("generic"), 1)
+        # interactive = button+link+textbox+searchbox+checkbox = 5
+        self.assertEqual(interactive, 5)
+        self.assertEqual(chars, len(ARIA_SAMPLE))
+        self.assertEqual(
+            digest, hashlib.sha256(ARIA_SAMPLE.encode()).hexdigest())
+
+    def test_hash_stable_and_changes_with_text(self):
+        _, _, _, h1 = BROWSER.parse_a11y(ARIA_SAMPLE)
+        _, _, _, h2 = BROWSER.parse_a11y(ARIA_SAMPLE)
+        self.assertEqual(h1, h2)
+        _, _, _, h3 = BROWSER.parse_a11y(ARIA_SAMPLE + "- link \"x\"")
+        self.assertNotEqual(h1, h3)
+
+    def test_empty_and_no_roles(self):
+        roles, interactive, chars, _ = BROWSER.parse_a11y("")
+        self.assertEqual(roles, {})
+        self.assertEqual(interactive, 0)
+        self.assertEqual(chars, 0)
+        roles, interactive, _, _ = BROWSER.parse_a11y(
+            "plain text without roles\nsecond line")
+        self.assertEqual(roles, {})
+
+    def test_dict_tree_fallback_counts_roles(self):
+        tree = {"role": "WebArea", "name": "x", "children": [
+            {"role": "heading", "name": "h"},
+            {"role": "link", "name": "l"},
+            {"role": "button", "name": "b"}]}
+        roles, interactive, chars, _ = BROWSER.parse_a11y(tree)
+        self.assertEqual(roles.get("heading"), 1)
+        self.assertEqual(roles.get("link"), 1)
+        self.assertEqual(roles.get("button"), 1)
+        self.assertEqual(interactive, 2)
+        self.assertGreater(chars, 0)
+
+
+class ExpandBboxTest(unittest.TestCase):
+    def test_center_small_change_expands_to_min_size(self):
+        # 1px 变化在 (32,24)：margin 8 -> 17x17，再扩到 32x32。
+        box = BROWSER.expand_bbox(32, 24, 33, 25, 1280, 800)
+        self.assertEqual(box, {"x": 17, "y": 9,
+                               "width": 32, "height": 32})
+
+    def test_top_edge_extends_downward_not_full_height(self):
+        # 贴顶边的变化：y=0 侧扩不动，向下补足 32，不拉满 800。
+        box = BROWSER.expand_bbox(120, 10, 128, 20, 1280, 800)
+        self.assertEqual(box["y"], 0)
+        self.assertEqual(box["height"], 32)
+        self.assertEqual(box["width"], 32)
+
+    def test_corner_clamps_to_zero(self):
+        box = BROWSER.expand_bbox(0, 0, 1, 1, 1280, 800)
+        self.assertEqual(box["x"], 0)
+        self.assertEqual(box["y"], 0)
+        self.assertEqual(box["width"], 32)
+        self.assertEqual(box["height"], 32)
+
+    def test_full_frame_change_stays_full(self):
+        box = BROWSER.expand_bbox(0, 0, 1280, 800, 1280, 800)
+        self.assertEqual(box, {"x": 0, "y": 0, "width": 1280,
+                               "height": 800})
+
+    def test_image_smaller_than_min_size_takes_full_extent(self):
+        box = BROWSER.expand_bbox(10, 10, 11, 11, 20, 20)
+        self.assertEqual(box, {"x": 0, "y": 0, "width": 20,
+                               "height": 20})
+
+
+class ComputeDiffTest(unittest.TestCase):
+    def test_identical_frames_no_change(self):
+        png = solid_png(64, 48)
+        changed, bbox = BROWSER.compute_diff_bbox(png, png)
+        self.assertFalse(changed)
+        self.assertIsNone(bbox)
+
+    def test_single_pixel_change_found_with_margin_and_min_size(self):
+        prev = solid_png(64, 48)
+        cur = encode_png(64, 48, {(32, 24): (0, 0, 0)})
+        changed, bbox = BROWSER.compute_diff_bbox(prev, cur)
+        self.assertTrue(changed)
+        self.assertEqual(bbox, {"x": 17, "y": 9,
+                                "width": 32, "height": 32})
+
+    def test_below_threshold_change_ignored(self):
+        # 每通道只差 5（阈值 10）：抗锯齿抖动级，不算变。
+        base = {(x, y): (100, 100, 100)
+                for x in range(64) for y in range(48)}
+        prev = encode_png(64, 48, base)
+        cur_pixels = dict(base)
+        cur_pixels[(32, 24)] = (105, 105, 105)
+        cur = encode_png(64, 48, cur_pixels)
+        changed, _ = BROWSER.compute_diff_bbox(prev, cur)
+        self.assertFalse(changed)
+
+    def test_single_channel_change_above_threshold_counts(self):
+        # 只蓝通道差 50：亮度加权会把它压到 ~6，逐通道阈值必须抓到。
+        base = {(x, y): (100, 100, 100)
+                for x in range(64) for y in range(48)}
+        prev = encode_png(64, 48, base)
+        cur_pixels = dict(base)
+        cur_pixels[(32, 24)] = (100, 100, 150)
+        cur = encode_png(64, 48, cur_pixels)
+        changed, bbox = BROWSER.compute_diff_bbox(prev, cur)
+        self.assertTrue(changed)
+        self.assertIsNotNone(bbox)
+
+    def test_size_mismatch_is_full_frame_change(self):
+        prev = solid_png(64, 48)
+        cur = solid_png(32, 24)
+        changed, bbox = BROWSER.compute_diff_bbox(prev, cur)
+        self.assertTrue(changed)
+        self.assertEqual(bbox, {"x": 0, "y": 0, "width": 32,
+                                "height": 24})
+
+
+class SnapshotEnrichTest(unittest.TestCase):
+    def test_snapshot_carries_role_counts(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            agent, _c, _h = _agent([FakePage()], tmp)
+            agent.open("https://example.com")
+            snap = agent.snapshot()
+            self.assertTrue(snap["ok"])
+            self.assertEqual(snap["a11y_roles"]["heading"], 2)
+            self.assertEqual(snap["a11y_roles"]["link"], 1)
+            self.assertEqual(snap["a11y_interactive"], 5)
+            self.assertEqual(snap["a11y_chars"], len(ARIA_SAMPLE))
+            self.assertEqual(
+                snap["a11y_hash"],
+                hashlib.sha256(ARIA_SAMPLE.encode()).hexdigest())
+
+    def test_snapshot_hash_changes_when_page_changes(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            page = FakePage(aria="- link \"a\"")
+            agent, _c, _h = _agent([page], tmp)
+            agent.open("https://example.com")
+            h1 = agent.snapshot()["a11y_hash"]
+            page._aria = "- link \"b\""
+            h2 = agent.snapshot()["a11y_hash"]
+            self.assertNotEqual(h1, h2)
+
+
+class DiffShotTest(unittest.TestCase):
+    def test_first_shot_is_full_frame_change(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            page = FakePage()
+            agent, _c, _h = _agent([page], tmp)
+            agent.open("https://example.com")
+            resp = agent.diff_shot()
+            self.assertTrue(resp["ok"])
+            self.assertTrue(resp["changed"])
+            self.assertEqual(resp["bbox"], {"x": 0, "y": 0,
+                                            "width": 1280,
+                                            "height": 800})
+            self.assertGreater(resp["size"], 0)
+            self.assertGreater(resp["full_size"], 0)
+            self.assertTrue(resp["path"].endswith(".jpg"))
+            with open(resp["path"], "rb") as fh:
+                self.assertEqual(fh.read(2), b"\xff\xd8")
+            # clip 调的是全视口 bbox。
+            self.assertEqual(page.shots[-1],
+                             ("jpeg", 70, resp["bbox"]))
+
+    def test_identical_second_shot_skipped(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            agent, _c, _h = _agent([FakePage()], tmp)
+            agent.open("https://example.com")
+            first = agent.diff_shot()
+            self.assertTrue(first["changed"])
+            second = agent.diff_shot()
+            self.assertTrue(second["ok"])
+            self.assertFalse(second["changed"])
+            self.assertEqual(second["size"], 0)
+            self.assertIsNone(second["path"])
+            self.assertIsNone(second["bbox"])
+            self.assertEqual(agent.status()["counters"]["shots_skipped"],
+                             1)
+            self.assertEqual(agent.status()["counters"]["shots_diff"],
+                             1)
+
+    def test_local_change_clips_to_bbox(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            page = FakePage()
+            agent, _c, _h = _agent([page], tmp)
+            agent.open("https://example.com")
+            agent.diff_shot()
+            page.set_frame(encode_png(64, 48, {(32, 24): (0, 0, 0)}))
+            resp = agent.diff_shot()
+            self.assertTrue(resp["changed"])
+            self.assertEqual(resp["bbox"], {"x": 17, "y": 9,
+                                            "width": 32,
+                                            "height": 32})
+            # 裁剪图字节里带 bbox 坐标（假实现按 clip 编码）。
+            self.assertIn(b"CLIP-17-9-32-32",
+                          open(resp["path"], "rb").read())
+            self.assertLess(resp["size"], resp["full_size"])
+
+    def test_open_keeps_diff_baseline_across_navigation(self):
+        # open 不清基线：同像素帧重导航后 diff_shot 应判无变化
+        # （上一帧就是这帧）；帧变了才判变化，且 bbox 为真实差异区。
+        with tempfile.TemporaryDirectory() as tmp:
+            page = FakePage()
+            agent, _c, _h = _agent([page, page], tmp)
+            agent.open("https://example.com")
+            agent.diff_shot()
+            agent.diff_shot()
+            agent.open("https://example.org")
+            same = agent.diff_shot()
+            self.assertTrue(same["ok"])
+            self.assertFalse(same["changed"])
+            page.set_frame(encode_png(64, 48, {(32, 24): (0, 0, 0)}))
+            changed = agent.diff_shot()
+            self.assertTrue(changed["changed"])
+            self.assertEqual(changed["bbox"], {"x": 17, "y": 9,
+                                               "width": 32,
+                                               "height": 32})
+
+    def test_close_clears_diff_baseline(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            page = FakePage()
+            agent, _c, _h = _agent([page], tmp)
+            agent.open("https://example.com")
+            agent.diff_shot()
+            agent.diff_shot()
+            agent.close()
+            self.assertFalse(agent.diff_shot()["ok"])
+            agent.open("https://example.com")
+            resp = agent.diff_shot()
+            self.assertTrue(resp["changed"])
+            self.assertEqual(resp["bbox"], {"x": 0, "y": 0,
+                                            "width": 1280,
+                                            "height": 800})
+
+
+class VerifyShotTest(unittest.TestCase):
+    def test_verify_shot_is_full_frame(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            agent, _c, _h = _agent([FakePage()], tmp)
+            agent.open("https://example.com")
+            resp = agent.verify_shot()
+            self.assertTrue(resp["ok"])
+            self.assertEqual(resp["format"], "jpeg")
+            self.assertEqual(resp["quality"], 70)
+            self.assertEqual(resp["width"], 1280)
+            self.assertTrue(resp["path"].endswith(".jpg"))
+            self.assertEqual(agent.status()["counters"]["shots_verify"],
+                             1)
+            # verify 不带 clip：假实现最后一次截图无 clip 参数。
+            self.assertEqual(agent._pages["default"].shots[-1],
+                             ("jpeg", 70, None))
+
+
+class CountersTest(unittest.TestCase):
+    def test_counters_and_verify_share(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            page = FakePage()
+            agent, _c, _h = _agent([page], tmp)
+            agent.open("https://example.com")
+            agent.screenshot()               # full +1
+            agent.screenshot(diff_only=True)  # skip +1（同帧）
+            agent.diff_shot()                # diff +1（首帧）
+            agent.diff_shot()                # skip +1（同帧）
+            agent.verify_shot()              # verify +1
+            st = agent.status()
+            self.assertEqual(st["counters"], {
+                "shots_full": 1, "shots_diff": 1,
+                "shots_verify": 1, "shots_skipped": 2})
+            self.assertAlmostEqual(st["verify_share"], 1 / 3)
+
+    def test_verify_share_zero_when_no_shots(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            agent, _c, _h = _agent([FakePage()], tmp)
+            st = agent.status()
+            self.assertEqual(st["verify_share"], 0.0)
+            self.assertEqual(st["counters"]["shots_full"], 0)
+
+
+class PillowMissingTest(unittest.TestCase):
+    def test_diff_shot_without_pillow_errors_and_names_fallback(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            agent, _c, _h = _agent([FakePage()], tmp)
+            agent.open("https://example.com")
+            before = agent.status()["counters"]
+
+            def _no_pillow():
+                raise RuntimeError(
+                    "diff_shot 需要 Pillow（No module named 'PIL'）："
+                    "镜像里 pip 未装 pillow，无法逐像素比对与裁剪；"
+                    "回落：用 screenshot 全帧 JPEG q70")
+
+            with mock.patch.object(BROWSER, "_load_pillow",
+                                   side_effect=_no_pillow):
+                resp = agent.diff_shot()
+            self.assertFalse(resp["ok"])
+            self.assertIn("Pillow", resp["error"])
+            self.assertIn("screenshot", resp["error"])
+            self.assertEqual(resp["fallback"], "screenshot")
+            # 不计入计数器、不落盘。
+            self.assertEqual(agent.status()["counters"], before)
+            self.assertEqual(
+                [f for f in os.listdir(tmp) if f.endswith(".jpg")],
+                [])
+
+
+class ForbiddenOpsTest(unittest.TestCase):
+    def test_forbidden_ops_still_rejected(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            agent, _c, _h = _agent([FakePage()], tmp)
+            for op in ("evaluate", "content", "devtools", "js"):
+                resp = BROWSER.handle_request(agent, {"op": op})
+                self.assertFalse(resp["ok"], op)
+
+    def test_new_ops_routed(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            agent, _c, _h = _agent([FakePage()], tmp)
+            agent.open("https://example.com")
+            self.assertTrue(BROWSER.handle_request(
+                agent, {"op": "diff_shot"})["ok"])
+            self.assertTrue(BROWSER.handle_request(
+                agent, {"op": "verify_shot"})["ok"])
+            resp = BROWSER.handle_request(agent, {"op": "nope"})
+            self.assertFalse(resp["ok"])
+            self.assertIn("diff_shot", resp["error"])
+            self.assertIn("verify_shot", resp["error"])
+
+
+class BuildWiringTest(unittest.TestCase):
+    def test_build_sh_installs_pillow_with_playwright(self):
+        text = (ROOT / "chv-guest" / "build.sh").read_text()
+        self.assertIn("playwright pillow", text)
+        # 两分支（--break-system-packages 与回落）都加 pillow。
+        self.assertEqual(text.count("playwright pillow"), 2)
+
+    def test_buildinfo_declares_pillow(self):
+        self.assertIn("pillow", BUILDINFO.BASE_CONTENTS)
+
+    def test_lockfile_still_declares_browser_script(self):
+        # chv-browser.py 改动仍随 repo_commit 登记（阶段 3 做法）。
+        for mod in (CHECK, GENERATE):
+            self.assertEqual(mod.DECLARED_SOURCES["chv-browser"],
+                             "repo_commit")
+
+    def test_lockfile_roundtrip_covers_pillow_via_pip(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            info = {
+                "tag": "chv-guest-24.04-0.164.0-alpha.9-test123",
+                "codex_version": "0.164.0-alpha.9",
+                "repo_commit": "test123",
+                "gt_version": "1.0.0",
+                "image_sha256": "a" * 64,
+                "chromium_pinned_rev": None,
+                "contents": list(BUILDINFO.BASE_CONTENTS),
+                "versions": {
+                    "dpkg": ["git 1:2.43.0-1ubuntu7",
+                             "ca-certificates 20240203",
+                             "cloud-init 24.1.3-0ubuntu3",
+                             "curl 8.5.0-2ubuntu10",
+                             "fontconfig 2.15.0-1.1ubuntu6",
+                             "fonts-wqy-microhei 0.2.0-beta-3.1",
+                             "openssh-client 1:9.6p1-3ubuntu13",
+                             "openssh-server 1:9.6p1-3ubuntu13",
+                             "python3 3.12.3-0ubuntu2",
+                             "python3-pip 24.0+dfsg-1ubuntu1",
+                             "systemd-container 255.4-1ubuntu8",
+                             "xz-utils 5.6.1+really5.4.5-1build0.1"],
+                    "pip": ["playwright==1.49.1",
+                            "pillow==10.2.0"],
+                    "gt": ["gt version 1.0.0"],
+                    "chromium": ["chromium_headless_shell-1248"],
+                },
+            }
+            buildinfo_path = os.path.join(tmp, "BUILDINFO.json")
+            with open(buildinfo_path, "w") as fh:
+                json.dump(info, fh)
+            lock_path = os.path.join(tmp, "lockfile.json")
+            self.assertEqual(
+                GENERATE.generate(buildinfo_path, lock_path), 0)
+            with open(lock_path) as fh:
+                lock = json.load(fh)
+            self.assertEqual(lock["unresolved"], [])
+            self.assertIn("pillow 10.2.0",
+                          lock["versions"]["pip"])
+            self.assertEqual(
+                GENERATE.verify(lock_path, buildinfo_path), 0)
+            self.assertEqual(
+                CHECK.main([sys.argv[0], buildinfo_path]), 0)
+
+
+if __name__ == "__main__":
+    unittest.main()