api: 下载响应头 X-Chunk-Count (卷数); db: get_file 带 chunk_count

api.py

@@ -75,7 +75,10 @@ async def download_file(file_id: str):
         return JSONResponse(status_code=404, content={"error": f"存储文件缺失: {path}"})
     # 解密参数: 任务 init 时存的 enc {alg, key_id, context}
     enc_params = json.dumps(rec["enc_params"], ensure_ascii=False)
-    headers = {"X-Enc-Params": base64.b64encode(enc_params.encode()).decode()}
+    headers = {
+        "X-Enc-Params": base64.b64encode(enc_params.encode()).decode(),
+        "X-Chunk-Count": str(rec["chunk_count"]),  # 客户端按卷粒度显示进度
+    }
     return FileResponse(
         path,
         filename=rec["file_name"],

db.py

@@ -196,10 +196,11 @@ class ServerDB:
         return [dict(r) for r in rows]
 
     def get_file(self, file_id: str) -> dict[str, Any] | None:
-        """单文件记录 (下载端点, 含解密参数 enc_params)"""
+        """单文件记录 (下载端点, 含解密参数 enc_params + 卷数)"""
         with self._conn() as conn:
             row = conn.execute(
-                "SELECT f.file_id, f.file_name, f.path, f.size, f.sha256, t.enc_params "
+                "SELECT f.file_id, f.file_name, f.path, f.size, f.sha256, "
+                "t.enc_params, t.chunk_count "
                 "FROM files f JOIN transfers t ON f.transfer_id = t.transfer_id "
                 "WHERE f.file_id = ?",
                 (file_id,),