diff --git a/app/api/canvas/[id]/route.ts b/app/api/canvas/[id]/route.ts
index 88af0bd0d..5b8f76aa8 100644
--- a/app/api/canvas/[id]/route.ts
+++ b/app/api/canvas/[id]/route.ts
@@ -4,6 +4,10 @@ import { db } from '@/lib/db';
 import { canvasProject } from '@/lib/db/schema';
 import { syncCanvasNodesForProject } from '@/lib/db/queries';
 import { eq, and } from 'drizzle-orm';
+import {
+  buildStaleCanvasSaveConflictPayload,
+  isStaleCanvasSaveBaseRevision,
+} from '@/lib/canvas/canvas-save-conflict';
 
 function resolveWorkspaceType(input: unknown) {
   return input === "agent" || input === "video" ? input : "canvas";
@@ -13,19 +17,6 @@ function getDefaultWorkspaceTitle(workspaceType: ReturnType<typeof resolveWorksp
   return workspaceType === "video" ? "未命名视频画布" : "未命名画布";
 }
 
-function parseRevisionDate(value: unknown) {
-  const raw = String(value || "").trim();
-  if (!raw) return null;
-  const parsed = new Date(raw);
-  return Number.isNaN(parsed.getTime()) ? null : parsed;
-}
-
-function isStaleBaseRevision(baseRevision: unknown, currentUpdatedAt: Date) {
-  const baseDate = parseRevisionDate(baseRevision);
-  if (!baseDate) return false;
-  return baseDate.getTime() + 1000 < currentUpdatedAt.getTime();
-}
-
 // 获取单个画布
 export async function GET(
   request: NextRequest,
@@ -95,15 +86,14 @@ export async function PUT(
       if (
         canvasData !== undefined &&
         baseCanvasRevision &&
-        isStaleBaseRevision(baseCanvasRevision, existingProject.updatedAt)
+        isStaleCanvasSaveBaseRevision({
+          baseCanvasRevision: body?.baseCanvasRevision,
+          baseCanvasUpdatedAt: body?.baseCanvasUpdatedAt,
+          currentUpdatedAt: existingProject.updatedAt,
+        })
       ) {
         return NextResponse.json(
-          {
-            success: false,
-            error: "画布已更新，请刷新后再保存",
-            code: "STALE_CANVAS_REVISION",
-            canvasUpdatedAt: existingProject.updatedAt.toISOString(),
-          },
+          buildStaleCanvasSaveConflictPayload(existingProject.updatedAt),
           { status: 409 }
         );
       }
diff --git a/lib/canvas/canvas-save-conflict.ts b/lib/canvas/canvas-save-conflict.ts
new file mode 100644
index 000000000..1a7364243
--- /dev/null
+++ b/lib/canvas/canvas-save-conflict.ts
@@ -0,0 +1,29 @@
+export const STALE_CANVAS_REVISION_CODE = "STALE_CANVAS_REVISION";
+
+export function parseCanvasRevisionDate(value: unknown) {
+  const raw = String(value || "").trim();
+  if (!raw) return null;
+  const parsed = new Date(raw);
+  return Number.isNaN(parsed.getTime()) ? null : parsed;
+}
+
+export function isStaleCanvasSaveBaseRevision(params: {
+  baseCanvasRevision?: unknown;
+  baseCanvasUpdatedAt?: unknown;
+  currentUpdatedAt: Date;
+}) {
+  const baseDate = parseCanvasRevisionDate(
+    params.baseCanvasUpdatedAt || params.baseCanvasRevision
+  );
+  if (!baseDate) return false;
+  return baseDate.getTime() + 1000 < params.currentUpdatedAt.getTime();
+}
+
+export function buildStaleCanvasSaveConflictPayload(currentUpdatedAt: Date) {
+  return {
+    success: false,
+    error: "画布已更新，请刷新后再保存",
+    code: STALE_CANVAS_REVISION_CODE,
+    canvasUpdatedAt: currentUpdatedAt.toISOString(),
+  };
+}
diff --git a/tests/routes/canvas-chat-helpers.test.ts b/tests/routes/canvas-chat-helpers.test.ts
index e36d6afe4..28fae44c4 100644
--- a/tests/routes/canvas-chat-helpers.test.ts
+++ b/tests/routes/canvas-chat-helpers.test.ts
@@ -64,6 +64,11 @@ import {
   getCanvasAgentOperationErrorMessage,
   normalizeCanvasAgentOperationErrorCode,
 } from "@/lib/canvas/agent-operation-errors";
+import {
+  buildStaleCanvasSaveConflictPayload,
+  isStaleCanvasSaveBaseRevision,
+  parseCanvasRevisionDate,
+} from "@/lib/canvas/canvas-save-conflict";
 import {
   applyCanvasOperationPlanToCanvasData,
   CanvasAgentMutationError,
@@ -125,6 +130,34 @@ import type { CanvasAgentContext } from "@/types/canvas/agent-protocol";
 import type { ChatMessage } from "@/lib/types";
 
 test.describe("canvas chat pure helpers", () => {
+  test("rejects stale autosave bases without blocking fresh or missing revisions", () => {
+    const currentUpdatedAt = new Date("2026-06-22T00:00:05.500Z");
+
+    expect(parseCanvasRevisionDate("not-a-date")).toBeNull();
+    expect(
+      isStaleCanvasSaveBaseRevision({
+        baseCanvasRevision: "2026-06-22T00:00:00.000Z",
+        currentUpdatedAt,
+      })
+    ).toBe(true);
+    expect(
+      isStaleCanvasSaveBaseRevision({
+        baseCanvasUpdatedAt: "2026-06-22T00:00:05.000Z",
+        currentUpdatedAt,
+      })
+    ).toBe(false);
+    expect(
+      isStaleCanvasSaveBaseRevision({
+        currentUpdatedAt,
+      })
+    ).toBe(false);
+    expect(buildStaleCanvasSaveConflictPayload(currentUpdatedAt)).toMatchObject({
+      success: false,
+      code: "STALE_CANVAS_REVISION",
+      canvasUpdatedAt: "2026-06-22T00:00:05.500Z",
+    });
+  });
+
   const plannerContext: CanvasAgentContext = {
     version: 1,
     source: "canvas",