fix(file): 公共 Downloads 使用 MediaStore 写入，兼容华为设备

- Android 10+ 公共目录通过 MediaStore ContentResolver 写入
- 同时写入缓存文件供 openFile 使用
- 避免华为设备 mkdirs()/writeBytes() ENOENT 问题

sdk-core/src/main/java/com/xuqm/sdk/file/FileSDK.kt

@@ -251,7 +251,12 @@ object FileSDK {
 
         val safeName = fileName.takeIf { it.isNotBlank() } ?: "download.bin"
 
-        // 尝试目标目录，如果 PublicDownloads 失败则回退到 Sandbox
+        // Android 10+ 公共 Downloads 目录使用 MediaStore 写入（兼容华为等设备）
+        if (destination == FileDownloadDestination.PublicDownloads && Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
+            return saveBlobViaMediaStore(context, bytes, safeName)
+        }
+
+        // 旧版本或 Sandbox 目录直接写文件
         val baseDir = resolveBaseDir(context, destination)
         val target = uniqueFile(baseDir, safeName)
         android.util.Log.d("XWV", "saveBlobDownload: writing to ${target.absolutePath}")
@@ -269,6 +274,44 @@ object FileSDK {
         }
     }
 
+    /**
+     * 通过 MediaStore 将文件写入公共 Downloads 目录。
+     * 在华为等设备上直接文件 I/O 会失败，MediaStore 通过 ContentResolver 操作，兼容性更好。
+     * 返回缓存目录中的副本（真实文件，可被 openFile 使用）。
+     */
+    private fun saveBlobViaMediaStore(context: Context, bytes: ByteArray, fileName: String): File {
+        val mimeType = MimeTypeMap.getSingleton()
+            .getMimeTypeFromExtension(fileName.substringAfterLast('.', "").lowercase())
+            ?: "application/octet-stream"
+        val appName = context.applicationInfo.loadLabel(context.packageManager).toString()
+
+        // 写入 MediaStore
+        val values = ContentValues().apply {
+            put(MediaStore.Downloads.DISPLAY_NAME, fileName)
+            put(MediaStore.Downloads.MIME_TYPE, mimeType)
+            put(MediaStore.Downloads.RELATIVE_PATH, "${Environment.DIRECTORY_DOWNLOADS}/$appName")
+            put(MediaStore.Downloads.IS_PENDING, 1)
+        }
+
+        val resolver = context.contentResolver
+        val uri = resolver.insert(MediaStore.Downloads.EXTERNAL_CONTENT_URI, values)
+            ?: throw java.io.IOException("MediaStore insert returned null")
+
+        resolver.openOutputStream(uri)?.use { out ->
+            out.write(bytes)
+        } ?: throw java.io.IOException("Cannot open output stream for $uri")
+
+        values.clear()
+        values.put(MediaStore.Downloads.IS_PENDING, 0)
+        resolver.update(uri, values, null, null)
+
+        android.util.Log.d("XWV", "saveBlobViaMediaStore: saved $fileName, size=${bytes.size}, uri=$uri")
+
+        // 同时写入缓存目录，供 openFile 使用
+        val cacheFile = File(context.cacheDir, fileName).apply { writeBytes(bytes) }
+        return cacheFile
+    }
+
     private fun resolveBaseDir(context: Context, destination: FileDownloadDestination): File = when (destination) {
         FileDownloadDestination.PublicDownloads -> {
             val appName = context.applicationInfo.loadLabel(context.packageManager).toString()