新增任务分享/导入功能并修复只读文件保存 EPERM

- flows: writeFlowFile 覆盖写加固(清只读属性->删除后 rename->覆盖写),
  外部复制导入的只读任务文件此前导致 flows:save EPERM 崩溃
- flows: exportFlowToPath/importFlowFromPath, 分享文件为单个 FlowDefinition
  JSON(.rpaflow.json); 导入校验 schemaVersion/nodes/edges, id 冲突时生成
  imported_ 前缀新 id 绝不覆盖既有任务
- IPC: flows:export 弹保存对话框 / flows:import 弹多选打开对话框,
  失败文件逐个汇报不阻塞其余
- preload: flows.export/flows.import; shared: FlowsImportResult 类型
- TasksPage: 头部「导入任务」按钮 + 每行「分享」按钮; App 接线与 toast
- 测试: 导出/导入往返、id 冲突、非法文件原因、只读覆盖共 4 例(7/7 绿)

src/main/flows.ts

@@ -242,11 +242,61 @@ export function saveFlow(input: FlowDefinition): FlowDefinition {
       appVersion: app.getVersion()
     }
   };
-  const target = fileOf(flow.id);
+  writeFlowFile(fileOf(flow.id), flow);
+  return flow;
+}
+
+/** 覆盖写任务文件。Windows 上目标文件带只读属性（外部导入/复制来的文件常见）或被占用时，
+ *  rename 会抛 EPERM——这里依次尝试：清除只读属性后 rename → 删除后 rename → 直接覆盖写。 */
+function writeFlowFile(target: string, flow: FlowDefinition): void {
   const temp = `${target}.tmp`;
   fs.writeFileSync(temp, JSON.stringify(flow, null, 2), "utf8");
-  fs.renameSync(temp, target);
-  return flow;
+  const retryable = (error: unknown): boolean => {
+    const code = (error as NodeJS.ErrnoException)?.code;
+    return code === "EPERM" || code === "EACCES" || code === "EBUSY";
+  };
+  const cleanupTemp = () => {
+    try {
+      fs.unlinkSync(temp);
+    } catch {
+      // 清理失败不影响主流程
+    }
+  };
+  try {
+    fs.renameSync(temp, target);
+    return;
+  } catch (error) {
+    if (!retryable(error)) {
+      cleanupTemp();
+      throw error;
+    }
+  }
+  try {
+    fs.chmodSync(target, 0o666);
+  } catch {
+    // 清只读属性失败不阻塞后续删除/覆盖尝试
+  }
+  try {
+    fs.unlinkSync(target);
+  } catch {
+    // 目标可能被其他进程占用，删除失败继续走覆盖写
+  }
+  try {
+    fs.renameSync(temp, target);
+    return;
+  } catch {
+    // rename 仍失败（目标被锁定），尝试直接覆盖
+  }
+  try {
+    fs.copyFileSync(temp, target);
+    cleanupTemp();
+  } catch (error) {
+    cleanupTemp();
+    throw new Error(
+      `任务文件被占用或无写入权限（${path.basename(target)}）。请关闭可能打开该文件的编辑器/网盘同步后再试。`,
+      { cause: error }
+    );
+  }
 }
 
 export function deleteFlow(id: string): void {
@@ -254,3 +304,64 @@ export function deleteFlow(id: string): void {
   if (fs.existsSync(target)) fs.unlinkSync(target);
 }
 
+/** 任务分享文件扩展名：单文件就是一个 FlowDefinition JSON，便于直接审阅/版本管理 */
+const SHARE_EXTENSION = "rpaflow";
+
+function normalizeImportedName(raw: unknown): string {
+  const name = String(raw ?? "").trim();
+  return name || "导入的任务";
+}
+
+/** 校验并归一化外部任务文件内容，不合法时抛出带原因的 Error */
+function parseSharedFlow(raw: string, source: string): FlowDefinition {
+  let data: unknown;
+  try {
+    data = JSON.parse(raw);
+  } catch {
+    throw new Error(`${source}：不是有效的 JSON 文件`);
+  }
+  const flow = data as FlowDefinition;
+  if (!flow || typeof flow !== "object") throw new Error(`${source}：文件内容不是任务结构`);
+  if (flow.schemaVersion !== 1) throw new Error(`${source}：schemaVersion 不是 1（版本不兼容）`);
+  if (!Array.isArray(flow.nodes) || !Array.isArray(flow.edges)) {
+    throw new Error(`${source}：缺少 nodes/edges 结构`);
+  }
+  if (flow.nodes.length > 2000) throw new Error(`${source}：节点数超过上限 2000`);
+  return flow;
+}
+
+/** 从分享文件导入任务：id 冲突时生成新 id，避免覆盖既有任务 */
+export function importFlowFromPath(filePath: string): FlowDefinition {
+  const raw = fs.readFileSync(filePath, "utf8");
+  const flow = parseSharedFlow(raw, path.basename(filePath));
+  const now = new Date().toISOString();
+  let id = typeof flow.id === "string" && ID_PATTERN.test(flow.id) ? flow.id : "";
+  if (!id || fs.existsSync(fileOf(id))) {
+    // 冲突/缺 id：基于名称生成可读 id，追加随机尾巴保证唯一
+    const seed = normalizeImportedName(flow.name)
+      .replace(/[^A-Za-z0-9]+/g, "_")
+      .replace(/^_+|_+$/g, "")
+      .slice(0, 40)
+      .toLowerCase();
+    const base = `imported_${seed || "task"}`;
+    id = `${base}_${Date.now().toString(36)}_${Math.random().toString(36).slice(2, 6)}`;
+    while (!ID_PATTERN.test(id)) id = `imported_task_${Date.now().toString(36)}`;
+  }
+  const imported: FlowDefinition = {
+    ...flow,
+    id,
+    name: normalizeImportedName(flow.name),
+    meta: { ...flow.meta, createdAt: flow.meta?.createdAt || now }
+  };
+  return saveFlow(imported);
+}
+
+/** 导出任务到指定路径（main 侧先用 dialog 拿到路径） */
+export function exportFlowToPath(id: string, targetPath: string): string {
+  const flow = getFlow(id);
+  fs.writeFileSync(targetPath, JSON.stringify(flow, null, 2), "utf8");
+  return targetPath;
+}
+
+export { SHARE_EXTENSION };
+