接入原生壳分享卡图片导出

新增 file.exportImage 宿主能力契约

分享卡下载在原生壳中优先走宿主图片导出

Expo 壳写入缓存图片并调用系统分享保存

Tauri 壳通过保存对话框写入图片字节

补齐能力漂移检查、测试和架构文档

src/services/host-bridge/hostBridge.test.ts

@@ -6,6 +6,7 @@ import type { HostBridgeCapability } from '../../../packages/shared/src/contract
 import {
   canUseHostShareGrid,
   canUseNativeHostCapability,
+  exportHostImageFile,
   exportHostTextFile,
   getHostRuntime,
   getNativeAppHostRuntime,
@@ -443,6 +444,7 @@ describe('hostBridge', () => {
         'app.openExternalUrl',
         'app.setTitle',
         'share.open',
+        'file.exportImage',
       ]),
     );
     window.__TAURI__ = {
@@ -482,6 +484,13 @@ describe('hostBridge', () => {
         url: 'https://app.genarrative.world/works/detail?work=PZ-1',
       }),
     ).resolves.toBe(true);
+    await expect(
+      exportHostImageFile({
+        fileName: '分享卡.png',
+        base64Data: 'c2hhcmUtY2FyZA==',
+        mimeType: 'image/png',
+      }),
+    ).resolves.toBe(true);
 
     expect(invoke).toHaveBeenCalledWith('host_bridge_request', {
       request: expect.objectContaining({
@@ -545,6 +554,17 @@ describe('hostBridge', () => {
         },
       }),
     });
+    expect(invoke).toHaveBeenCalledWith('host_bridge_request', {
+      request: expect.objectContaining({
+        method: 'file.exportImage',
+        payload: {
+          fileName: '分享卡.png',
+          base64Data: 'c2hhcmUtY2FyZA==',
+          mimeType: 'image/png',
+        },
+        timeoutMs: 30000,
+      }),
+    });
   });
 
   test('原生 App 宿主不支持能力时回退到 H5 路径', async () => {
@@ -598,15 +618,29 @@ describe('hostBridge', () => {
         url: 'https://app.genarrative.world/works/detail?work=PZ-1',
       }),
     ).resolves.toBe(false);
+    await expect(
+      exportHostImageFile({
+        fileName: '分享卡.png',
+        base64Data: 'c2hhcmUtY2FyZA==',
+        mimeType: 'image/png',
+      }),
+    ).resolves.toBe(false);
   });
 
-  test('普通浏览器不处理宿主文本导出', async () => {
+  test('普通浏览器不处理宿主文件导出', async () => {
     await expect(
       exportHostTextFile({
         fileName: '作品记录.txt',
         content: 'content',
       }),
     ).resolves.toBe(false);
+    await expect(
+      exportHostImageFile({
+        fileName: '分享卡.png',
+        base64Data: 'c2hhcmUtY2FyZA==',
+        mimeType: 'image/png',
+      }),
+    ).resolves.toBe(false);
   });
 
   test('原生 App 宿主通过 HostBridge 导出文本文件', async () => {
@@ -694,4 +728,57 @@ describe('hostBridge', () => {
       }),
     ).resolves.toBe(false);
   });
+
+  test('原生 App 宿主通过 HostBridge 导出图片文件', async () => {
+    const invoke = vi.fn(
+      async (_command: string, args?: Record<string, unknown>) => {
+        const request = (args as { request: { id: string } }).request;
+        return {
+          bridge: 'GenarrativeHostBridge',
+          version: 1,
+          id: request.id,
+          ok: true,
+          result: {
+            action: 'saved',
+            fileName: '分享卡.png',
+            bytes: 10,
+          },
+        };
+      },
+    );
+    window.history.replaceState(
+      null,
+      '',
+      nativeAppPath(['file.exportImage']),
+    );
+    window.__TAURI__ = {
+      core: {
+        invoke: asTauriInvoke(invoke),
+      },
+    };
+
+    await expect(
+      exportHostImageFile({
+        fileName: '分享卡.png',
+        base64Data: 'c2hhcmUtY2FyZA==',
+        mimeType: 'image/png',
+      }),
+    ).resolves.toEqual({
+      action: 'saved',
+      fileName: '分享卡.png',
+      bytes: 10,
+    });
+
+    expect(invoke).toHaveBeenCalledWith('host_bridge_request', {
+      request: expect.objectContaining({
+        method: 'file.exportImage',
+        payload: {
+          fileName: '分享卡.png',
+          base64Data: 'c2hhcmUtY2FyZA==',
+          mimeType: 'image/png',
+        },
+        timeoutMs: 30000,
+      }),
+    });
+  });
 });