feat(trading): 清空购物车落步骤证据，补空车/有商品两场景测试

- clear_cart 返回清理后 cart 页最终 HTML（best-effort，抓取失败不掩盖清理结果）
- runner step 0 落 00-cart-clear.{html,meta.json} 并登记 evidence_index，
  证据先于闸门判断落盘（清理未净被拦时这份现场就是排查依据）；
  仍是本机卫生步骤：不上报 gateway、不记 order_events
- /api/cart/clear 响应不携带 html（路由显式挑字段，与 cart_add 同风格）
- 单测：fake page 覆盖空车/有商品/HTML 抓取失败；runner 层覆盖证据落盘
  与闸门拦截场景
- 真账号复验 scripts/verify_cart_clear.py：空车 removed=0/count=0；
  加购 1 件后 clear removed=1/count=0，status 复核 101

tests/test_site_interact.py

@@ -6,6 +6,8 @@ _extract_error_message）——这三者覆盖了「从商品页 HTML 抽加购
 
 SiteInteractor 类的 add_to_cart / verify_cart 涉及 Playwright，不在离线测试覆盖
 范围；只在 test_worker_runner.py 里用桩站点覆盖 runner 与 site 的契约。
+clear_cart 与 _dump_debug_snapshot 用不依赖 Playwright 的 fake page 覆盖了方法
+自身逻辑（见文件尾部对应小节），真实站点行为仍由 scripts/ 真账号脚本验证。
 """
 from __future__ import annotations
 
@@ -33,6 +35,7 @@ from app.trading.worker.site_interact import (
     OrderStatusSnapshot,
     SiteInteractor,
     _accumulate_order_list_page,
+    _DELETE_BUTTON_SELECTOR,
     _extract_error_message,
     _extract_purchase_fields,
     _OrderListAccumulator,
@@ -1214,4 +1217,160 @@ async def test_query_cart_count_unparseable_body_raises():
         await site._query_cart_count()
 
 
+# ---- clear_cart：空车 / 有商品两个场景的核心逻辑（fake page，不依赖 Playwright）----
+#
+# 真实站点行为（SPA 是否点一个少一个、确认 modal 是否存在）由真账号脚本验证
+# （scripts/verify_cart_empty.py、scripts/verify_cart_clear.py）；这里覆盖的是
+# 方法自身的逻辑：空车立即结束、有商品时循环点「削除」直到按钮消失、最终页面
+# HTML 进返回值、HTML 抓取失败不掩盖清理结果。
+
+
+class _FakeDeleteButton:
+    """「削除」按钮替身：还有剩余按钮时 wait_for 成功，click 消耗一个（模拟 SPA
+    点完一个就把该项从 DOM 摘掉）"""
+
+    def __init__(self, page: "_FakeClearCartPage"):
+        self._page = page
+
+    async def wait_for(self, *, state: str, timeout: int) -> None:
+        if self._page.delete_buttons_left <= 0:
+            raise RuntimeError("模拟 Playwright 等待超时：没有删除按钮了")
+
+    async def click(self) -> None:
+        self._page.delete_buttons_left -= 1
+
+
+class _FakeMissingButton:
+    """确认 modal 按钮替身：永远不出现（站点是否弹 modal 未实测，按不存在处理）"""
+
+    async def wait_for(self, *, state: str, timeout: int) -> None:
+        raise RuntimeError("模拟 Playwright 等待超时：无确认 modal")
+
+    async def click(self) -> None:
+        raise AssertionError("没有可见的确认按钮，不应触发点击")
+
+
+class _FakeLocator:
+    def __init__(self, button: Any):
+        self.first = button
+
+
+class _FakeClearCartPage:
+    """cart 页替身：实现 clear_cart 用到的全部 page 接口"""
+
+    def __init__(self, *, delete_buttons: int, html: str):
+        self.delete_buttons_left = delete_buttons
+        self._html = html
+        self.closed = False
+
+    def locator(self, selector: str) -> _FakeLocator:
+        if selector == _DELETE_BUTTON_SELECTOR:
+            return _FakeLocator(_FakeDeleteButton(self))
+        return _FakeLocator(_FakeMissingButton())
+
+    async def goto(self, url: str, *, wait_until: str, timeout: int) -> None:
+        return None
+
+    async def wait_for_function(self, *args: Any, **kwargs: Any) -> None:
+        return None
+
+    async def wait_for_load_state(self, *args: Any, **kwargs: Any) -> None:
+        return None
+
+    async def wait_for_timeout(self, *args: Any, **kwargs: Any) -> None:
+        return None
+
+    async def content(self) -> str:
+        return self._html
+
+    async def close(self) -> None:
+        self.closed = True
+
+
+class _FakeClearCartContext:
+    """BrowserContext 替身：new_page 返回 fake cart 页，request 回固定 count body"""
+
+    def __init__(self, *, page: _FakeClearCartPage, count_body: str):
+        self.page = page
+        self.request = _FakeCartCountRequest(count_body)
+
+    async def new_page(self) -> _FakeClearCartPage:
+        return self.page
+
+
+class _FakeLoggedInAuth:
+    """AuthSession 替身：require_logged_in 直接放行"""
+
+    async def require_logged_in(self, site: str) -> None:
+        return None
+
+
+def _build_clear_cart_site(*, delete_buttons: int, count_body: str, html: str) -> SiteInteractor:
+    """构造 clear_cart 可离线跑起来的 SiteInteractor（fake page + fake count API）"""
+    site = SiteInteractor(auth_session=_FakeLoggedInAuth(), settings=None)  # type: ignore[arg-type]
+    site._context = _FakeClearCartContext(
+        page=_FakeClearCartPage(delete_buttons=delete_buttons, html=html),
+        count_body=count_body,
+    )  # type: ignore[assignment]
+
+    async def _noop_refresh() -> None:
+        return None
+
+    site._refresh_context_if_stale = _noop_refresh  # type: ignore[assignment]
+    return site
+
+
+_EMPTY_COUNT_BODY = 'callBack({"status":"101","message":"value not found.","count":""})'
+
+
+async def test_clear_cart_empty_cart_returns_success_without_clicks():
+    """场景 1：购物车没有商品 —— 找不到「削除」按钮立即结束，按清理成功返回
+
+    空车时 count API 返回 status=101（合法空车），cart_count 必须是 0 而不是
+    -1（2026-08-16 修复过的误判）；removed_count=0，最终页面 HTML 照常带回。
+    """
+    site = _build_clear_cart_site(
+        delete_buttons=0, count_body=_EMPTY_COUNT_BODY, html="<html>empty cart</html>",
+    )
+
+    result = await site.clear_cart()
+
+    assert result == {"removed_count": 0, "cart_count": 0, "html": "<html>empty cart</html>"}
+    assert site._context.page.closed is True  # 页面必须关，不能泄漏
+
+
+async def test_clear_cart_with_items_clicks_until_no_button_left():
+    """场景 2：购物车有商品 —— 循环点第一个「削除」，点一个少一个，直到按钮消失
+
+    每次循环都重新查 selector（避免索引漂移），3 件商品应点 3 次；清空后 count
+    API 回 status=101 → cart_count=0，最终页面 HTML 进返回值。
+    """
+    site = _build_clear_cart_site(
+        delete_buttons=3, count_body=_EMPTY_COUNT_BODY, html="<html>cleared cart</html>",
+    )
+
+    result = await site.clear_cart()
+
+    assert result["removed_count"] == 3
+    assert result["cart_count"] == 0
+    assert result["html"] == "<html>cleared cart</html>"
+    assert site._context.page.closed is True
+
+
+async def test_clear_cart_html_capture_failure_keeps_clear_result():
+    """最终页面 HTML 抓取失败（如页面异常）不掩盖清理结果本身：html 记空串"""
+    site = _build_clear_cart_site(
+        delete_buttons=0, count_body=_EMPTY_COUNT_BODY, html="",
+    )
+
+    async def _broken_content() -> str:
+        raise RuntimeError("page already closed")
+
+    site._context.page.content = _broken_content  # type: ignore[assignment]
+
+    result = await site.clear_cart()
+
+    assert result == {"removed_count": 0, "cart_count": 0, "html": ""}
+
+
 # ---- helper ----