diff --git a/mateclaw-ui/src/components/chat/MessageBubble.vue b/mateclaw-ui/src/components/chat/MessageBubble.vue
index 2ca034a6..31732931 100644
--- a/mateclaw-ui/src/components/chat/MessageBubble.vue
+++ b/mateclaw-ui/src/components/chat/MessageBubble.vue
@@ -537,6 +537,7 @@ import {
 } from '@element-plus/icons-vue'
 import { useStreamingMarkdown } from '@/composables/useStreamingMarkdown'
 import { buildGeneratedFileNameMap, linkifyGeneratedFileUrls } from '@/utils/generatedFileLinks'
+import { ensureModelViewer } from '@/utils/lazyModelViewer'
 import { useAuthenticatedAttachment } from '@/composables/useAuthenticatedAttachment'
 import { useToolLabel } from '@/composables/useToolLabel'
 import { http } from '@/api'
@@ -901,9 +902,14 @@ watch(audioAttachments, (atts) => {
   if (atts.length > 0) loadAllAudios(atts)
 }, { immediate: true })
 // 3D models also need the auth-blob loader — <model-viewer src> doesn't carry
-// the Authorization header any more than <img>/<audio> do.
+// the Authorization header any more than <img>/<audio> do. The heavy
+// @google/model-viewer Web Component is lazy-loaded here (only when a bubble
+// actually has a 3D attachment) instead of eagerly in main.ts.
 watch(model3dAttachments, (atts) => {
-  if (atts.length > 0) loadAllModels(atts)
+  if (atts.length > 0) {
+    ensureModelViewer()
+    loadAllModels(atts)
+  }
 }, { immediate: true })
 
 // --- 时间 ---
diff --git a/mateclaw-ui/src/main.ts b/mateclaw-ui/src/main.ts
index 0c126bcb..c9d38ee1 100644
--- a/mateclaw-ui/src/main.ts
+++ b/mateclaw-ui/src/main.ts
@@ -9,10 +9,10 @@ import router from './router'
 import './assets/main.css'
 import { i18n, initializeLocale } from './i18n'
 
-// Side-effect import: registers the <model-viewer> Web Component globally so
-// generated 3D assets (.glb) can be previewed inline in chat bubbles. Vue's
-// compiler is told to treat the tag as a custom element via vite.config.ts.
-import '@google/model-viewer'
+// Note: the heavy <model-viewer> Web Component is no longer imported here. It is
+// lazy-registered on demand (see src/utils/lazyModelViewer.ts) the first time a
+// chat bubble renders a 3D (.glb) asset, keeping it out of the initial bundle.
+// Vue's compiler still treats <model-viewer> as a custom element via vite.config.ts.
 
 async function bootstrap() {
   await initializeLocale()
diff --git a/mateclaw-ui/src/utils/lazyModelViewer.ts b/mateclaw-ui/src/utils/lazyModelViewer.ts
new file mode 100644
index 00000000..0cdce896
--- /dev/null
+++ b/mateclaw-ui/src/utils/lazyModelViewer.ts
@@ -0,0 +1,22 @@
+/**
+ * Lazy registrar for the <model-viewer> Web Component.
+ *
+ * @google/model-viewer is a heavy dependency (~hundreds of KB) that used to be
+ * imported eagerly in main.ts, landing it in the initial entry chunk on every
+ * first paint even though 3D (.glb) previews are rare. This defers the import to
+ * the first time a chat bubble actually renders a 3D attachment. The module-level
+ * promise makes it a process-wide singleton — the component registers exactly
+ * once no matter how many bubbles request it.
+ *
+ * Vue's compiler still treats <model-viewer> as a custom element via the
+ * isCustomElement option in vite.config.ts, so the tag resolves whether or not
+ * the definition has loaded yet; once this import resolves the element upgrades.
+ */
+let loadPromise: Promise<unknown> | null = null
+
+export function ensureModelViewer(): Promise<unknown> {
+  if (!loadPromise) {
+    loadPromise = import('@google/model-viewer')
+  }
+  return loadPromise
+}
diff --git a/mateclaw-ui/vite.config.ts b/mateclaw-ui/vite.config.ts
index 063575b4..5283eabc 100644
--- a/mateclaw-ui/vite.config.ts
+++ b/mateclaw-ui/vite.config.ts
@@ -88,18 +88,38 @@ export default defineConfig({
         //      chunk lets each Worker on the chunk run with a smaller
         //      working set, which is what blew up the Docker build at
         //      1.3.0 (needed --max-old-space-size=6144 as a band-aid).
-        manualChunks: {
-          'vendor-monaco': ['monaco-editor', '@guolao/vue-monaco-editor'],
-          'vendor-vue-flow': [
-            '@vue-flow/core',
-            '@vue-flow/background',
-            '@vue-flow/controls',
-            '@vue-flow/minimap',
-          ],
-          'vendor-mermaid': ['mermaid'],
-          'vendor-echarts': ['echarts'],
-          'vendor-element': ['element-plus', '@element-plus/icons-vue'],
-          'vendor-markdown': ['marked', 'marked-highlight', 'highlight.js', 'dompurify'],
+        //
+        // Function form (not the object map) so we can ISOLATE the CommonJS
+        // interop helpers into their own tiny chunk. With the object form,
+        // Rollup hoisted the shared `commonjsHelpers` module into
+        // vendor-mermaid / vendor-markdown; because the eager entry chunk needs
+        // that helper, it gained a *static* import of both ~1 MB vendor chunks,
+        // and Vite then `modulepreload`-ed them on first paint even though
+        // mermaid/markdown are only used on the (lazy) chat route. Splitting the
+        // helper into its own leaf chunk lets the entry depend on a few-hundred-
+        // byte module instead, so the heavy vendors stay purely on-demand.
+        manualChunks(id) {
+          // Isolate shared runtime helpers FIRST — before the node_modules gate.
+          // The Vite preload helper (\0vite/preload-helper, exported as the
+          // __vitePreload used by every lazy route import) and the CommonJS
+          // interop helpers are virtual modules with no node_modules path. If one
+          // lands inside a heavy vendor chunk, the entry's route-lazy imports pull
+          // that whole chunk in as a static dependency and Vite preloads it. A
+          // dedicated leaf chunk keeps them out of the vendors.
+          if (id.includes('vite/preload-helper') || id.includes('commonjsHelpers')
+              || id.includes('commonjs-dynamic-modules') || id.includes('\0commonjs')) {
+            return 'vendor-runtime'
+          }
+          if (!id.includes('node_modules')) return undefined
+          if (id.includes('monaco-editor') || id.includes('vue-monaco-editor')) return 'vendor-monaco'
+          if (id.includes('@vue-flow')) return 'vendor-vue-flow'
+          if (id.includes('/mermaid/')) return 'vendor-mermaid'
+          if (id.includes('/echarts/') || id.includes('zrender')) return 'vendor-echarts'
+          if (id.includes('element-plus') || id.includes('@element-plus')) return 'vendor-element'
+          if (id.includes('/marked') || id.includes('highlight.js') || id.includes('dompurify')) {
+            return 'vendor-markdown'
+          }
+          return undefined
         },
       },
     },