diff --git a/apps/mall/components/shell/CategoryMenu.vue b/apps/mall/components/shell/CategoryMenu.vue
index b83fb45..8bcd373 100644
--- a/apps/mall/components/shell/CategoryMenu.vue
+++ b/apps/mall/components/shell/CategoryMenu.vue
@@ -2,6 +2,8 @@
 import { topCategories, childCategories } from "~/mock/data";
 import { t as pick } from "@vmall/shared";
 
+const props = withDefaults(defineProps<{ pinned?: boolean }>(), { pinned: false });
+
 const { locale } = useI18n();
 const open = ref(false);
 const hoverId = ref<string | null>(null);
@@ -19,7 +21,7 @@ defineExpose({ open });
 </script>
 
 <template>
-  <div class="catmenu" @mouseleave="hoverId = null">
+  <div class="catmenu" :class="{ pinned: props.pinned }" @mouseleave="hoverId = null">
     <ul class="lvl1">
       <li
         v-for="g in cats"
@@ -62,6 +64,15 @@ defineExpose({ open });
   display: flex;
   width: 960px;
 }
+/* pinned: in-flow left rail of the home hero row, flyout overlays the carousel */
+.catmenu.pinned {
+  position: relative;
+  top: auto;
+  left: auto;
+  flex: none;
+  width: 240px;
+  height: 450px;
+}
 .lvl1 {
   width: 240px;
   margin: 0;
@@ -131,4 +142,20 @@ defineExpose({ open });
 .sub-items a:hover {
   color: var(--mall-red);
 }
+/* pinned overrides: 240x450 rail, flyout opens to the right over the carousel */
+.catmenu.pinned .lvl1 {
+  box-sizing: border-box;
+  height: 450px;
+  min-height: 450px;
+}
+.catmenu.pinned .sub {
+  position: absolute;
+  top: 0;
+  left: 240px;
+  box-sizing: border-box;
+  width: 700px;
+  height: 450px;
+  min-height: 450px;
+  overflow: auto;
+}
 </style>
diff --git a/apps/mall/components/shell/SiteHeader.vue b/apps/mall/components/shell/SiteHeader.vue
index 97aacf9..01b027b 100644
--- a/apps/mall/components/shell/SiteHeader.vue
+++ b/apps/mall/components/shell/SiteHeader.vue
@@ -32,19 +32,14 @@ onMounted(async () => {
 
 const menuOpen = ref(false);
 const isHome = computed(() => route.path === "/");
-const collapsed = ref(false);
-onMounted(() => {
-  const onScroll = (): void => {
-    collapsed.value = window.scrollY > 200;
-  };
-  window.addEventListener("scroll", onScroll, { passive: true });
-});
-const showMenu = computed(() => menuOpen.value || (isHome.value && !collapsed.value));
+// The home page pins the category menu in the hero row instead, so the header
+// dropdown is hover-only and only on non-home pages.
+const showMenu = computed(() => menuOpen.value && !isHome.value);
 </script>
 
 <template>
   <header class="hdr">
-    <div v-show="!collapsed" class="w1200 hdr-top">
+    <div class="w1200 hdr-top">
       <NuxtLink to="/" class="logo">VMall</NuxtLink>
       <div class="search-box">
         <input
diff --git a/apps/mall/pages/index.vue b/apps/mall/pages/index.vue
index dabb7f7..2d76d78 100644
--- a/apps/mall/pages/index.vue
+++ b/apps/mall/pages/index.vue
@@ -9,7 +9,10 @@ const floors = computed(() => homeFloors().filter((f) => f.products.length > 0))
 <template>
   <div>
     <div class="w1200 hero">
-      <UiCarousel :images="MOCK_BANNERS" :height="450" />
+      <ShellCategoryMenu pinned />
+      <div class="hero-slider">
+        <UiCarousel :images="MOCK_BANNERS" :height="450" />
+      </div>
     </div>
 
     <div class="w1200 strip">
@@ -49,7 +52,14 @@ const floors = computed(() => homeFloors().filter((f) => f.products.length > 0))
 
 <style scoped>
 .hero {
+  display: flex;
+  height: 450px;
   margin-top: 0;
+  background: #fff;
+}
+.hero-slider {
+  flex: 1;
+  min-width: 0;
 }
 .strip {
   display: flex;
diff --git a/openspec/changes/pin-home-category-menu/.openspec.yaml b/openspec/changes/pin-home-category-menu/.openspec.yaml
new file mode 100644
index 0000000..d28e909
--- /dev/null
+++ b/openspec/changes/pin-home-category-menu/.openspec.yaml
@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-09-17
diff --git a/openspec/changes/pin-home-category-menu/proposal.md b/openspec/changes/pin-home-category-menu/proposal.md
new file mode 100644
index 0000000..a1dda0e
--- /dev/null
+++ b/openspec/changes/pin-home-category-menu/proposal.md
@@ -0,0 +1,29 @@
+# Proposal
+
+## Why
+
+The mall home page shows the category menu as a hover dropdown that auto-hides once the shopper scrolls 200px, and the hero carousel spans the full 1200px grid. Referencing tigshop's B2B2C storefront, the category tree should be a permanent left rail beside the banner so shoppers always see the catalog structure without hovering or scrolling back up. Additionally, the header's scroll-collapse hides the logo/search/cart bar on scroll, which hurts usability.
+
+## What Changes
+
+- Home page hero becomes a flex row: a pinned 240px category sidebar (reusing `ShellCategoryMenu`) left of the carousel; both are 450px tall and in-flow, not overlaid.
+- Carousel narrows from 1200px to ~950px; banner images (1200×450) are center-cropped left/right at fixed 450px height.
+- Hovering a top-level category in the pinned sidebar expands the white mega-menu panel to the right, overlaying the carousel (same content as today's flyout).
+- Non-home pages keep the hover dropdown under the nav "全部商品分类" entry, unchanged.
+- **BREAKING** (visual): the header no longer auto-hides on scroll — the `collapsed`/`scrollY > 200` logic is removed entirely, so the logo/search/cart bar and category menu never auto-hide.
+
+## Capabilities
+
+### New Capabilities
+
+(none)
+
+### Modified Capabilities
+
+- `frontend-mall`: the "Mock PC home page" requirement gains a pinned category sidebar beside the cropped carousel; the "B2B2C mall-style PC storefront shell" requirement changes the category mega-menu to hover-only on non-home pages and removes scroll-based header auto-hide.
+
+## Non-goals
+
+- No changes to mock category data, banner assets, or the search/category filtering logic.
+- No changes to apps/shop-admin, apps/admin, the shared package, or the backend.
+- No right-side user rail, no extra promo tiles in the hero (options B/C/D from the visual proposal were rejected; see `docs/visual-proposal/home-hero-options.html`).
diff --git a/openspec/changes/pin-home-category-menu/specs/frontend-mall/spec.md b/openspec/changes/pin-home-category-menu/specs/frontend-mall/spec.md
new file mode 100644
index 0000000..653883f
--- /dev/null
+++ b/openspec/changes/pin-home-category-menu/specs/frontend-mall/spec.md
@@ -0,0 +1,33 @@
+# Spec Delta
+
+## MODIFIED Requirements
+
+### Requirement: Mock PC home page
+The mall home page SHALL render a hero row composed of a pinned 240px category sidebar on the left and a hero carousel filling the remainder of the 1200px grid, both 450px tall and occupying layout space (not overlaid). The sidebar SHALL list all top-level categories with up to three child links each; hovering a top-level category SHALL expand the mega-menu panel to the right over the carousel. Banner images SHALL render at fixed 450px height, center-cropped horizontally to the narrower carousel width. Below the hero, the page SHALL render a six-item quick-link strip with promotion tiles and bilingual product floors with a left advert and product-card grid.
+
+#### Scenario: shopper lands on home
+- **WHEN** `/` loads in mock mode
+- **THEN** the category sidebar is visible to the left of the carousel without any hover or click, the carousel renders center-cropped banners at 450px height, and the quick links, promotions and every non-empty product floor render fixed mock content
+
+#### Scenario: sidebar stays while scrolling
+- **WHEN** a shopper scrolls the home page beyond 200px
+- **THEN** the category sidebar remains rendered in the hero row and does not auto-hide
+
+#### Scenario: expand a category
+- **WHEN** a shopper hovers a top-level category in the pinned sidebar
+- **THEN** the mega-menu panel expands to the right, overlaying the carousel with that category's child and grandchild links
+
+### Requirement: B2B2C mall-style PC storefront shell
+The mall SHALL render a buyer-facing desktop shell modeled on a classic B2B2C PC mall: a 30px utility bar, logo/search/cart header, dark primary navigation with a hover category mega-menu, a 1200px content grid, and a value-proposition footer. The header SHALL remain fully visible while scrolling; no part of the shell SHALL auto-hide based on scroll position. The category mega-menu SHALL appear as a hover dropdown under the navigation "All Categories" entry on every page except the home page, where it is instead pinned in the hero row. The visual language SHALL use #ca151e for brand/price/active states, #f5f5f5 section backgrounds, gray hairline borders, compact controls, and product-card hover lift/shadow. The implementation SHALL use Nuxt-native semantic components and SHALL NOT depend on Element Plus.
+
+#### Scenario: shopper opens any mall page
+- **WHEN** a shopper navigates to a buyer-facing route
+- **THEN** the shared desktop shell wraps the route content and its nav/search/cart controls are usable
+
+#### Scenario: header persists while scrolling
+- **WHEN** a shopper scrolls any mall page
+- **THEN** the logo/search/cart header bar remains visible and is never collapsed or hidden by scroll position
+
+#### Scenario: hover categories on a non-home page
+- **WHEN** a shopper hovers "All Categories" in the navigation on a page other than `/`
+- **THEN** the category mega-menu dropdown appears below the navigation and hides again on mouse leave
diff --git a/openspec/changes/pin-home-category-menu/tasks.md b/openspec/changes/pin-home-category-menu/tasks.md
new file mode 100644
index 0000000..6649b8b
--- /dev/null
+++ b/openspec/changes/pin-home-category-menu/tasks.md
@@ -0,0 +1,20 @@
+# Tasks
+
+## 1. CategoryMenu pinned mode
+
+- [x] 1.1 Add a `pinned` boolean prop to `apps/mall/components/shell/CategoryMenu.vue`; when `pinned` is true, render `.catmenu` in-flow (`position: relative; top: auto; width: 240px`) instead of the absolute 960px dropdown, and keep the default (dropdown) rendering unchanged for the header use
+- [x] 1.2 In pinned mode, keep the `.lvl1` sidebar at 240px wide and 450px tall, and reposition the `.sub` flyout as `position: absolute; left: 240px; top: 0; width: ~700px; height: 450px` so it overlays the carousel area to the right; keep existing hover state, links, and i18n untouched
+
+## 2. Home hero row
+
+- [x] 2.1 In `apps/mall/pages/index.vue`, change the `.hero` block to a flex row: `<ShellCategoryMenu pinned />` followed by `UiCarousel`; fix the row height at 450px so the sidebar and carousel align
+- [x] 2.2 Ensure banner images center-crop horizontally at the new ~950px carousel width (fixed 450px height, `object-fit: cover` — verify `UiCarousel` already applies this, adjust if not); do not modify the mock SVG assets
+
+## 3. Header cleanup
+
+- [x] 3.1 In `apps/mall/components/shell/SiteHeader.vue`, remove the `collapsed` ref, the scroll listener, and the `v-show="!collapsed"` on `.hdr-top`; reduce `showMenu` to `menuOpen && !isHome` so the header mega-menu is hover-only and suppressed on the home page, where the category menu is pinned in the hero row instead (per `specs/frontend-mall/spec.md`; decision confirmed during apply)
+
+## 4. Verification
+
+- [x] 4.1 Run `pnpm --filter @vmall/mall build` and confirm it passes
+- [x] 4.2 Start the mall dev server and verify in a real browser: home shows the pinned sidebar left of the cropped carousel with no hover; scrolling past 200px keeps both the header and sidebar visible; hovering a top-level category expands the panel over the carousel; a non-home page (e.g. `/search`) shows the hover dropdown and no pinned sidebar