feat(billing): ?plan= 深链用一句文案指向目标卡，而不是第三层描边

D13 把 URL 高亮改成纯滚动定位后留下一个空档：桌面上三张套餐卡本来就都在
视口内，滚动等于什么都没指。付费转化路径上，用户从「开通年度会员」的链接
进来，看不到任何东西指向那张卡。

产品在「加一行文案 / 维持现状 / 把描边加回来」里选了第一个。

用卡片自己的套餐名，不用序数——手机端 [data-plan-alias="monthly"] 带
order:-1，序数会指错。新增断言锁住这两点（必须有 note、不得出现序数写法）。

测试 3354 不变，fail 仍 31 且与基线逐条一致；/ 仍 Static；
干净构建 CSS gzip 39,724→39,733。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0193vBv6w5MV2cifdTUu9H5P

frontend/DESIGN.md

@@ -488,6 +488,7 @@ page. Three parts now, in reading order:
 
 - **Structure:** summary line (balance · membership / expiry), then tabs 会员套餐 / 点数包 / 兑换码 / 订单记录.
 - **Plan card states:** exactly two, and they are mutually exclusive. `.is-current` (当前套餐) draws the `--color-action` border; `.is-recommended` (推荐, the monthly plan) draws the `--color-border-strong` border on the plain canvas. A card that is both takes 当前套餐 — its own action is 续费, not 立即购买 — so borders and fills can never stack. The badge in the card header says the same word. Mobile ordering (月卡 first below 640px) keys off `[data-plan-alias="monthly"]`, i.e. the plan's identity, not its state, so it survives the card becoming the current plan.
+- **`?plan=` deep link:** names its target in copy, not in a third border layer. A `.membership-plan-note` line above the grid reads 「你从「年度会员」的链接过来的，就在下面。」, and the card takes `ref` / `tabIndex` / `aria-current` for the scroll and focus target only. It names the plan by the card's own title rather than a position: below 640px the monthly card takes `order: -1`, so an ordinal would point at the wrong card. Scrolling alone is not wayfinding here — at desktop widths all three cards are already in view, so a link that only scrolled pointed at nothing.
 - **Actions:** recommended-plan purchase is `Button` default. Other plan and credit buys use `Button` outline. Cashier still opens with `window.open` in a new tab. Paying copy is 跳转收银台…; pending copy is 等待支付结果. Redeem is an inline form on its tab, not a nested dialog.
 - **Deep links:** `/?settings=billing&source=…[&plan=…][&tab=…]` open this pane on `/` and are then stripped. `/membership` and `/membership/orders` redirect here. `&plan=` does **not** repaint the card (that used to be a third border plus an outline on top of the two states); it scrolls the card into view and focuses it, and nothing else.
 - **Waiting:** the summary renders from the in-memory account. Package cards stay empty until `/api/payment/packages` arrives. No spinner, skeleton, or 「正在加载」.

frontend/src/app/globals.css

@@ -4308,6 +4308,12 @@ button.nav-rail-identity:hover { background: var(--sidebar-accent); }
    borders and backgrounds can never stack the way the three old BEM modifiers
    (recommended / current / URL highlight) did. Plan order on mobile is keyed off the
    plan identity below, not off a state, so it survives the card becoming 当前套餐. */
+.membership-plan-note {
+  margin: 0 0 var(--space-3);
+  color: var(--color-ink-secondary);
+  font-size: var(--type-caption);
+  line-height: 1.55;
+}
 .membership-plan-card.is-recommended { border-color: var(--color-border-strong); background: var(--color-canvas); }
 .membership-plan-card.is-current { border-color: var(--color-action); }
 .membership-card-header { display: flex; align-items: flex-start; justify-content: space-between; gap: var(--space-3); }

frontend/src/components/billing-panel.tsx

@@ -62,6 +62,11 @@ export function BillingPanel({ account: seedAccount, highlightedPlan, initialTab
     setRedeemMessage,
   } = billing;
   const plans = selectMembershipPlans(paymentPackages);
+  /* Named by the card's own title, not by position: on phones the monthly card
+     takes `order: -1`, so an ordinal would point at the wrong card. */
+  const highlightedName = highlightedPlan
+    ? plans.find((product) => planAlias(product) === highlightedPlan)?.name ?? null
+    : null;
   const creditPacks = paymentPackages.filter((product) => product.productType === "credit_pack");
   const credits = account?.credits ?? seedAccount.credits;
 
@@ -119,6 +124,13 @@ export function BillingPanel({ account: seedAccount, highlightedPlan, initialTab
 
         <TabsContent className="membership-panel" value="membership">
           {packagesSettled && !packagesError && !paymentEnabled && <p className="membership-empty">在线支付暂未开放。</p>}
+          {/* A ?plan= deep link no longer tints or outlines the card it points at
+              (D13: one card, one state). On desktop all three cards are visible
+              anyway, so scrolling alone pointed at nothing — this line is the
+              wayfinding, in copy instead of a third border layer. */}
+          {highlightedName && (
+            <p className="membership-plan-note">你从「{highlightedName}」的链接过来的，就在下面。</p>
+          )}
           {plans.length > 0 && (
             <div className="membership-plan-grid">
               {plans.map((product) => {

frontend/tests/billing-panel.test.ts

@@ -216,6 +216,13 @@ test("plan param forces the membership segment and highlights the matching card"
   assert.match(panelSource, /ref=\{highlighted \? highlightedCardRef : undefined\}/);
   assert.match(panelSource, /aria-current=\{highlighted \? "true" : undefined\}/);
   assert.match(panelSource, /highlightedCardRef/);
+  // 滚动定位本身在桌面上指不到任何东西——三张卡本来就都在视口里。所以深链必须
+  // 另有一句文字说明它指向哪张卡，且必须用卡片自己的名字而不是序数：手机端
+  // `[data-plan-alias="monthly"]` 带 order:-1，序数会指错。
+  assert.match(panelSource, /const highlightedName = highlightedPlan/);
+  assert.match(panelSource, /plans\.find\(\(product\) => planAlias\(product\) === highlightedPlan\)\?\.name/);
+  assert.match(panelSource, /className="membership-plan-note"/);
+  assert.doesNotMatch(panelSource, /第 \{[\s\S]{0,120}\} 张/);
   assert.match(hookSource, /scrollIntoView\(\{ behavior: "smooth", block: "center" \}\)/);
   assert.match(hookSource, /card\.focus\(\{ preventScroll: true \}\)/);
   assert.match(hookSource, /initialTab: input\.highlightedPlan \? "membership" : input\.initialTab/);