diff --git a/apps/web/src/shared/components/FlowchartEditor/index.vue b/apps/web/src/shared/components/FlowchartEditor/index.vue
index 91125fc..d4556bb 100644
--- a/apps/web/src/shared/components/FlowchartEditor/index.vue
+++ b/apps/web/src/shared/components/FlowchartEditor/index.vue
@@ -19,6 +19,7 @@ import { getNodeTypeConfig } from "./useNodeStyles"
 import { useHistory } from "./useHistory"
 import { useFlowOperations } from "./useFlowOperations"
 import { useCache } from "./useCache"
+import { toPortableEdges, toPortableNodes } from "./serialize"
 import CustomNode from "./CustomNode.vue"
 import { useProblemStore } from "oj/store/problem"
 
@@ -120,10 +121,21 @@ const handleRedo = () => {
   }
 }
 
-// 清空画布
+// 清空画布。工具栏那个按钮点一下就全没了，且 clearCache() 会连本题存着的草稿
+// 一起删掉，刷新也找不回来 —— 学生误点的代价太大，加一道确认
+const dialog = useDialog()
 const handleClear = () => {
-  clearCanvas()
-  clearCache()
+  if (nodes.value.length === 0 && edges.value.length === 0) return
+  dialog.warning({
+    title: "清空画布",
+    content: "画布上的内容会被清掉，这道题存着的草稿也会一起删除。确定吗？",
+    positiveText: "清空",
+    negativeText: "再想想",
+    onPositiveClick: () => {
+      clearCanvas()
+      clearCache()
+    },
+  })
 }
 
 // 键盘事件
@@ -139,10 +151,12 @@ const handleKeyDown = (event: KeyboardEvent) => {
   }
 
   if (event.ctrlKey || event.metaKey) {
-    if (event.key === "z" && !event.shiftKey) {
+    const key = event.key.toLowerCase()
+    if (key === "z" && !event.shiftKey) {
       event.preventDefault()
       handleUndo()
-    } else if (event.key === "z" && event.shiftKey) {
+    } else if ((key === "z" && event.shiftKey) || key === "y") {
+      // 工具栏上的提示写的就是 Ctrl+Y，但原来只实现了 Ctrl+Shift+Z，按 Y 没反应
       event.preventDefault()
       handleRedo()
     }
@@ -188,9 +202,10 @@ const setFlowchartData = (data: { nodes: Node[]; edges: Edge[] }) => {
 defineExpose({
   nodes,
   edges,
+  // 提交出去的这份会压缩后长期存进数据库，同样裁掉运行时内部字段
   getFlowchartData: () => ({
-    nodes: nodes.value,
-    edges: edges.value,
+    nodes: toPortableNodes(nodes.value),
+    edges: toPortableEdges(edges.value),
   }),
   setFlowchartData,
 })
diff --git a/apps/web/src/shared/components/FlowchartEditor/serialize.ts b/apps/web/src/shared/components/FlowchartEditor/serialize.ts
new file mode 100644
index 0000000..e9bb63b
--- /dev/null
+++ b/apps/web/src/shared/components/FlowchartEditor/serialize.ts
@@ -0,0 +1,45 @@
+import type { Edge, Node } from "@vue-flow/core"
+
+/**
+ * 把画布上的节点/连线裁成「可持久化」的形状。
+ *
+ * 画布里的 node 是 vue-flow 的 GraphNode：除了我们自己塞进去的字段，它还挂着
+ * `dimensions` / `computedPosition` / `handleBounds` / `selected` / `dragging` /
+ * `resizing` / `initialized` / `isParent` / `events` 一堆运行时内部状态（见
+ * vue-flow 的 parseNode）。这些东西会跟着一起：
+ *
+ *   - 写进 localStorage（每次改动都写一次）
+ *   - 进 20 份历史快照，每份都要 JSON 深拷贝一遍
+ *   - 压缩后提交进数据库，长期存着
+ *
+ * 实测一个两节点的图就能撑到 600+ 字节，其中大半是 handleBounds。而重新挂载时
+ * 这些字段全都会被重新计算，存下来没有任何意义 —— 还会把存档格式和 vue-flow
+ * 的内部实现绑死，将来升级或迁移数据都要跟着动。
+ *
+ * `style` 保留：它是建节点时按类型算好的（见 useNodeStyles），丢了会让恢复出来
+ * 的图变样。
+ */
+export function toPortableNodes(nodes: Node[]) {
+  return nodes.map((node) => ({
+    id: node.id,
+    type: node.type,
+    position: {
+      x: node.position?.x ?? 0,
+      y: node.position?.y ?? 0,
+    },
+    data: node.data,
+    style: node.style,
+  })) as Node[]
+}
+
+export function toPortableEdges(edges: Edge[]) {
+  return edges.map((edge) => ({
+    id: edge.id,
+    source: edge.source,
+    target: edge.target,
+    sourceHandle: edge.sourceHandle ?? null,
+    targetHandle: edge.targetHandle ?? null,
+    type: edge.type,
+    label: edge.label,
+  })) as Edge[]
+}
diff --git a/apps/web/src/shared/components/FlowchartEditor/useCache.ts b/apps/web/src/shared/components/FlowchartEditor/useCache.ts
index 2f61556..26daf31 100644
--- a/apps/web/src/shared/components/FlowchartEditor/useCache.ts
+++ b/apps/web/src/shared/components/FlowchartEditor/useCache.ts
@@ -1,6 +1,7 @@
 import { ref, toValue, watch, type Ref, type MaybeRefOrGetter } from "vue"
 import { useStorage, useDebounceFn } from "@vueuse/core"
 import type { Node, Edge } from "@vue-flow/core"
+import { toPortableEdges, toPortableNodes } from "./serialize"
 
 /**
  * 缓存管理 - 使用 @vueuse 的 useStorage
@@ -28,8 +29,8 @@ export function useCache(
 
   // 防抖保存：isSaving 在 watch 中置 true，保存完成后置 false，使 UI 能感知保存中状态
   const debouncedSave = useDebounceFn(() => {
-    storedData.value.nodes = nodes.value
-    storedData.value.edges = edges.value
+    storedData.value.nodes = toPortableNodes(nodes.value)
+    storedData.value.edges = toPortableEdges(edges.value)
     storedData.value.timestamp = new Date().toISOString()
     lastSaved.value = new Date()
     hasUnsavedChanges.value = false
@@ -39,8 +40,8 @@ export function useCache(
   // 立即保存
   const saveToCache = () => {
     isSaving.value = true
-    storedData.value.nodes = nodes.value
-    storedData.value.edges = edges.value
+    storedData.value.nodes = toPortableNodes(nodes.value)
+    storedData.value.edges = toPortableEdges(edges.value)
     storedData.value.timestamp = new Date().toISOString()
     lastSaved.value = new Date()
     hasUnsavedChanges.value = false
diff --git a/apps/web/src/shared/components/FlowchartEditor/useHistory.ts b/apps/web/src/shared/components/FlowchartEditor/useHistory.ts
index 94ced95..e4bf0cf 100644
--- a/apps/web/src/shared/components/FlowchartEditor/useHistory.ts
+++ b/apps/web/src/shared/components/FlowchartEditor/useHistory.ts
@@ -1,5 +1,6 @@
 import { shallowRef, computed } from "vue"
 import type { Node, Edge } from "@vue-flow/core"
+import { toPortableEdges, toPortableNodes } from "./serialize"
 
 /**
  * 简化的历史记录管理
@@ -18,7 +19,14 @@ export function useHistory() {
     nodes: Node[],
     edges: Edge[],
   ): { nodes: Node[]; edges: Edge[] } =>
-    JSON.parse(JSON.stringify({ nodes, edges })) as {
+    // 先裁掉 vue-flow 的运行时内部字段再深拷贝：20 份快照 × 每个节点几百字节的
+    // handleBounds/dimensions，纯属白拷
+    JSON.parse(
+      JSON.stringify({
+        nodes: toPortableNodes(nodes),
+        edges: toPortableEdges(edges),
+      }),
+    ) as {
       nodes: Node[]
       edges: Edge[]
     }