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.test.ts

@@ -1,4 +1,5 @@
-import { mkdir, mkdtemp, rm, writeFile } from "node:fs/promises";
+import { mkdir, mkdtemp, rm, chmod, writeFile } from "node:fs/promises";
+import { writeFileSync, readFileSync } from "node:fs";
 import os from "node:os";
 import path from "node:path";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
@@ -11,7 +12,7 @@ vi.mock("electron", () => ({
   }
 }));
 
-import { createDemoFlow, createExampleFlows, createFlow, listFlows, saveFlow } from "./flows";
+import { createDemoFlow, createExampleFlows, createFlow, exportFlowToPath, importFlowFromPath, listFlows, saveFlow } from "./flows";
 
 describe("flow summaries", () => {
   beforeEach(async () => {
@@ -64,3 +65,72 @@ describe("flow summaries", () => {
     expect(examples.find((flow) => flow.id === "example_error_route")?.edges.some((edge) => edge.sourceHandle === "error")).toBe(true);
   });
 });
+
+describe("flow share export/import", () => {
+  beforeEach(async () => {
+    electronState.userData = await mkdtemp(path.join(os.tmpdir(), "rpa-flow-share-"));
+  });
+
+  afterEach(async () => {
+    await rm(electronState.userData, { recursive: true, force: true });
+  });
+
+  it("exports a flow to a share file and re-imports it with a fresh id on conflict", async () => {
+    const flow = saveFlow(createFlow("密钥读取任务"));
+    const shareFile = path.join(electronState.userData, "share", "密钥读取任务.rpaflow.json");
+    await mkdir(path.dirname(shareFile), { recursive: true });
+    exportFlowToPath(flow.id, shareFile);
+
+    expect(JSON.parse(readFileSync(shareFile, "utf8")).id).toBe(flow.id);
+
+    // id 冲突：再次导入同一文件应生成新 id，不覆盖原任务
+    const imported = importFlowFromPath(shareFile);
+    expect(imported.id).not.toBe(flow.id);
+    expect(imported.name).toBe("密钥读取任务");
+    expect(listFlows().filter((item) => item.name === "密钥读取任务")).toHaveLength(2);
+  });
+
+  it("keeps the original id when importing a share file whose id is free", () => {
+    const shareFile = path.join(electronState.userData, "手工分享.rpaflow.json");
+    writeFileSync(shareFile, JSON.stringify({
+      schemaVersion: 1,
+      id: "manual_task_01",
+      name: "手工分享的任务",
+      description: "",
+      enabled: true,
+      trigger: { type: "manual", label: "手动运行" },
+      variables: [],
+      nodes: [{ id: "node_start", componentId: "Trigger.Manual", position: { x: 160, y: 120 }, values: {}, options: {} }],
+      edges: [],
+      meta: { createdAt: "2026-01-01T00:00:00.000Z", updatedAt: "2026-01-01T00:00:00.000Z", appVersion: "0.1.0" }
+    }), "utf8");
+
+    const imported = importFlowFromPath(shareFile);
+    expect(imported.id).toBe("manual_task_01");
+    expect(imported.name).toBe("手工分享的任务");
+  });
+
+  it("rejects invalid share files with a readable reason", () => {
+    const badJson = path.join(electronState.userData, "bad.rpaflow.json");
+    writeFileSync(badJson, "not json", "utf8");
+    expect(() => importFlowFromPath(badJson)).toThrow(/不是有效的 JSON/);
+
+    const badSchema = path.join(electronState.userData, "schema.rpaflow.json");
+    writeFileSync(badSchema, JSON.stringify({ schemaVersion: 99, nodes: [], edges: [] }), "utf8");
+    expect(() => importFlowFromPath(badSchema)).toThrow(/schemaVersion/);
+
+    const badStructure = path.join(electronState.userData, "structure.rpaflow.json");
+    writeFileSync(badStructure, JSON.stringify({ schemaVersion: 1, nodes: "no" }), "utf8");
+    expect(() => importFlowFromPath(badStructure)).toThrow(/nodes\/edges/);
+  });
+
+  it("overwrites a read-only flow file on save (imported file scenario)", async () => {
+    const flow = saveFlow(createFlow("只读任务"));
+    const target = path.join(electronState.userData, "flows", `${flow.id}.json`);
+    // 模拟外部复制进来带只读属性的导入文件
+    await chmod(target, 0o444);
+    expect(() => saveFlow({ ...flow, name: "只读任务-改" })).not.toThrow();
+    expect(JSON.parse(readFileSync(target, "utf8")).name).toBe("只读任务-改");
+    await chmod(target, 0o666);
+  });
+});