fix(canvas): 画布同步 - 版本冲突先核对并合并，本地保存与云端状态分开展示

本地持久化记录保存时间和日志令牌，同步面板区分本地与云端，不再用提示打断编辑。冲突时先尝试合并，无法合并才保留草稿并暂停自动提交；未登录时生成结果留在本地，登录后再继续上传。

web/src/services/diagnostics/client-diagnostics.ts

@@ -20,6 +20,8 @@ export type ClientDiagnosticEvent = {
     taskId?: string;
     projectId?: string;
     canvasId?: string;
+    nodes_before?: number;
+    nodes_after?: number;
     stack?: string;
 };
 
@@ -133,6 +135,8 @@ export function recordDiagnosticEvent(input: DiagnosticEventInput) {
         taskId: safeDiagnosticId(input.taskId),
         projectId: safeDiagnosticId(input.projectId),
         canvasId: safeDiagnosticId(input.canvasId),
+        nodes_before: input.nodes_before === undefined ? undefined : clampNumber(input.nodes_before, 0, 10_000_000),
+        nodes_after: input.nodes_after === undefined ? undefined : clampNumber(input.nodes_after, 0, 10_000_000),
         stack: redactClientText(input.stack, 4000),
     };
     events.push(event);