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

apps/mobile-shell/src/mobileHostBridge.test.ts

@@ -22,7 +22,12 @@ vi.mock('expo-clipboard', () => ({
 }));
 
 const writtenFiles = vi.hoisted(
-  () => [] as { uri: string; content: string }[],
+  () =>
+    [] as {
+      uri: string;
+      content: string;
+      options?: { encoding?: 'utf8' | 'base64' };
+    }[],
 );
 
 vi.mock('expo-file-system', () => ({
@@ -36,10 +41,11 @@ vi.mock('expo-file-system', () => ({
       this.uri = `file:///cache/${fileName}`;
     }
 
-    write(content: string) {
+    write(content: string, options?: { encoding?: 'utf8' | 'base64' }) {
       writtenFiles.push({
         uri: this.uri,
         content,
+        options,
       });
     }
   },
@@ -309,6 +315,7 @@ describe('handleMobileHostBridgeMessage', () => {
       {
         uri: 'file:///cache/作品-记录-.txt',
         content: '暖灯猫街',
+        options: undefined,
       },
     ]);
     expect(Sharing.shareAsync).toHaveBeenCalledWith(
@@ -352,4 +359,61 @@ describe('handleMobileHostBridgeMessage', () => {
     expect(writtenFiles).toEqual([]);
     expect(Sharing.shareAsync).not.toHaveBeenCalled();
   });
+
+  test('file.exportImage 写入缓存图片并调起系统分享', async () => {
+    const response = await send(
+      request('file.exportImage', {
+        fileName: ' ../分享:卡?.png ',
+        base64Data: 'c2hhcmUtY2FyZA==',
+        mimeType: 'image/png',
+      }),
+    );
+
+    const okResponse = expectOk(response);
+
+    expect(okResponse.result).toEqual({
+      action: 'saved',
+      fileName: '分享-卡-.png',
+      bytes: 10,
+    });
+    expect(writtenFiles).toEqual([
+      {
+        uri: 'file:///cache/分享-卡-.png',
+        content: 'c2hhcmUtY2FyZA==',
+        options: { encoding: 'base64' },
+      },
+    ]);
+    expect(Sharing.shareAsync).toHaveBeenCalledWith(
+      'file:///cache/分享-卡-.png',
+      {
+        mimeType: 'image/png',
+        UTI: 'public.png',
+        dialogTitle: '分享-卡-.png',
+      },
+    );
+  });
+
+  test('file.exportImage 拒绝非图片 MIME 与超限内容', async () => {
+    const unsupportedMime = await send(
+      request('file.exportImage', {
+        fileName: '分享卡.txt',
+        base64Data: 'c2hhcmUtY2FyZA==',
+        mimeType: 'text/plain',
+      }),
+    );
+
+    expect(expectFailed(unsupportedMime).error.code).toBe('invalid_request');
+
+    const oversized = await send(
+      request('file.exportImage', {
+        fileName: '分享卡.png',
+        base64Data: `${'A'.repeat(7 * 1024 * 1024)}`,
+        mimeType: 'image/png',
+      }),
+    );
+
+    expect(expectFailed(oversized).error.code).toBe('invalid_request');
+    expect(writtenFiles).toEqual([]);
+    expect(Sharing.shareAsync).not.toHaveBeenCalled();
+  });
 });