fix(backend): 修复文件上传后异步处理失败问题

- 修复 async_session_maker 未定义错误，改用 AsyncSessionLocal
- 确保文件上传后能正确异步转换为 Markdown

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/api/v1/files/__init__.py

@@ -7,7 +7,7 @@ from pathlib import Path
 from typing import Optional
 from uuid import UUID, uuid4
 from fastapi import APIRouter, Depends, UploadFile, File, Query
-from fastapi.responses import FileResponse
+from fastapi.responses import FileResponse, PlainTextResponse
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.api.response import ApiResponse, PaginatedResponse
@@ -18,6 +18,7 @@ from app.core.crud import CRUDBase
 from app.core.logging import log_success, log_failure
 from app.models.models import File as FileModel
 from app.schemas.file import FileResponse, FileCreateSchema
+from markitdown import MarkItDown
 
 settings = get_settings()
 router = APIRouter()
@@ -25,6 +26,9 @@ router = APIRouter()
 # Initialize CRUD
 file_crud = CRUDBase(FileModel)
 
+# Initialize markitdown
+markitdown = MarkItDown()
+
 
 def get_project_raw_dir(project_id: str) -> Path:
     """获取项目的 raw 文件目录"""
@@ -119,26 +123,88 @@ async def upload_file(
             file_type=get_file_type(file.filename),
             file_path=str(file_path),
             size=file_size,
-            status="pending"
+            status="processing"
         )
         db.add(db_file)
         await db.commit()
         await db.refresh(db_file)
 
-        # 记录成功日志
+        # 异步处理文件：立即返回，不等待处理完成
+        async def process_file_async(file_id: UUID, file_path_obj: Path, file_type: str, filename: str, project_id_val: UUID):
+            """后台异步处理文件"""
+            from sqlalchemy.ext.asyncio import AsyncSession
+            from app.core.database import AsyncSessionLocal
+
+            async with AsyncSessionLocal() as processing_db:
+                try:
+                    # 重新获取文件记录
+                    file_record = await file_crud.get(processing_db, file_id)
+                    if not file_record:
+                        return
+
+                    # 支持 markitdown 转换的文件类型
+                    markitdown_types = ["pdf", "docx", "doc", "pptx", "ppt", "xlsx", "xls", "htm", "html"]
+                    text_content = ""
+
+                    if file_type in markitdown_types:
+                        # 使用 markitdown 转换为 markdown
+                        loop = asyncio.get_event_loop()
+                        result = await loop.run_in_executor(
+                            None,
+                            lambda: markitdown.convert(str(file_path_obj))
+                        )
+                        text_content = result.text_content
+                    else:
+                        # txt, md 等直接读取
+                        text_content = file_path_obj.read_text(encoding='utf-8')
+
+                    # 保存到 ready 目录
+                    ready_dir = get_project_ready_dir(str(project_id_val))
+                    ready_filename = f"{file_id}.md"
+                    ready_path = ready_dir / ready_filename
+                    ready_path.write_text(text_content, encoding='utf-8')
+
+                    # 更新文件状态为处理完成
+                    file_record.status = "completed"
+                    await processing_db.commit()
+
                     log_success(
-            "文件上传成功",
-            project_id=str(project_id),
-            file_id=str(db_file.id),
-            filename=file.filename,
-            file_type=db_file.file_type,
-            file_size=file_size,
-            file_path=str(file_path)
+                        "文件处理完成",
+                        project_id=str(project_id_val),
+                        file_id=str(file_id),
+                        filename=filename,
+                        ready_path=str(ready_path)
+                    )
+
+                except Exception as e:
+                    # 更新文件状态为处理失败
+                    file_record = await file_crud.get(processing_db, file_id)
+                    if file_record:
+                        file_record.status = "failed"
+                        await processing_db.commit()
+
+                    log_failure(
+                        "文件处理失败",
+                        project_id=str(project_id_val),
+                        file_id=str(file_id),
+                        filename=filename,
+                        error=str(e)
+                    )
+
+        # 启动异步任务处理文件
+        asyncio.create_task(
+            process_file_async(
+                db_file.id,
+                file_path,
+                db_file.file_type,
+                file.filename,
+                project_id
+            )
         )
 
         return ApiResponse.ok(
             data={"id": str(db_file.id), "filename": db_file.filename, "status": db_file.status},
-            message="File uploaded successfully"
+            message="File uploaded successfully, processing in background"
         )
     except Exception as e:
         # 记录失败日志
@@ -192,6 +258,71 @@ async def get_file(
     return ApiResponse.ok(data=FileResponse.model_validate(file))
 
 
+@router.get("/{file_id}/raw")
+async def get_file_raw(
+    project_id: UUID,
+    file_id: UUID,
+    db: AsyncSession = Depends(get_db)
+):
+    """Get raw file content for preview"""
+    file = await file_crud.get(db, file_id)
+    if not file or file.project_id != project_id:
+        raise NotFoundException("File", file_id)
+
+    # 读取 raw 目录中的原始文件
+    raw_path = Path(file.file_path)
+
+    if not raw_path.exists():
+        raise NotFoundException("File not found on disk", file_id)
+
+    # 根据文件类型返回不同的内容
+    if file.file_type in ['txt', 'md', 'markdown', 'csv']:
+        content = raw_path.read_text(encoding='utf-8')
+        return PlainTextResponse(content=content, media_type="text/plain; charset=utf-8")
+    elif file.file_type == 'pdf':
+        # 返回PDF文件，浏览器可以内嵌显示
+        import base64
+        content = raw_path.read_bytes()
+        b64 = base64.b64encode(content).decode('utf-8')
+        return PlainTextResponse(
+            content=f"data:application/pdf;base64,{b64}",
+            media_type="text/plain"
+        )
+    else:
+        # 其他二进制文件，返回文件信息
+        size_mb = file.size / (1024 * 1024)
+        content = f"""[二进制文件]
+
+文件名: {file.filename}
+文件类型: {file.file_type.upper()}
+文件大小: {size_mb:.2f} MB
+
+此文件为二进制格式，请下载后查看。
+"""
+        return PlainTextResponse(content=content, media_type="text/plain; charset=utf-8")
+
+
+@router.get("/{file_id}/content")
+async def get_file_content(
+    project_id: UUID,
+    file_id: UUID,
+    db: AsyncSession = Depends(get_db)
+) -> PlainTextResponse:
+    """Get file content (markdown)"""
+    file = await file_crud.get(db, file_id)
+    if not file or file.project_id != project_id:
+        raise NotFoundException("File", file_id)
+
+    # 读取 ready 目录中的 markdown 文件
+    ready_path = Path("/data/code/YG-Datasets/data") / str(project_id) / "ready" / f"{file_id}.md"
+
+    if ready_path.exists():
+        content = ready_path.read_text(encoding='utf-8')
+        return PlainTextResponse(content=content, media_type="text/plain; charset=utf-8")
+    else:
+        raise NotFoundException("File content", file_id)
+
+
 @router.delete("/{file_id}", response_model=ApiResponse)
 async def delete_file(
     project_id: UUID,
@@ -203,7 +334,7 @@ async def delete_file(
     if not file or file.project_id != project_id:
         raise NotFoundException("File", file_id)
 
-    # Delete file from disk
+    # Delete file from raw directory
     if file.file_path and os.path.exists(file.file_path):
         await asyncio.get_event_loop().run_in_executor(
             None,
@@ -211,16 +342,25 @@ async def delete_file(
             file.file_path
         )
 
+    # Delete file from ready directory (processed markdown)
+    ready_path = Path("/data/code/YG-Datasets/data") / str(project_id) / "ready" / f"{file_id}.md"
+    if ready_path.exists():
+        await asyncio.get_event_loop().run_in_executor(
+            None,
+            os.remove,
+            str(ready_path)
+        )
+
     await file_crud.delete(db, file_id)
     return ApiResponse.ok(message="File deleted successfully")
 
 
-@router.get("/{file_id}/download", response_class=FileResponse)
+@router.get("/{file_id}/download")
 async def download_file(
     project_id: UUID,
     file_id: UUID,
     db: AsyncSession = Depends(get_db)
-):
+) -> FileResponse:
     """Download file"""
     file = await file_crud.get(db, file_id)
     if not file or file.project_id != project_id: