feat: 完善 MVP-2 演示和进度体验

app/main.py

@@ -1,15 +1,17 @@
 from collections.abc import AsyncGenerator
 from contextlib import asynccontextmanager
+import logging
 from urllib.parse import quote
 
 from fastapi import Depends, FastAPI, HTTPException, Request, status
-from fastapi.responses import HTMLResponse
+from fastapi.responses import HTMLResponse, JSONResponse
 from fastapi.responses import Response
 from fastapi.staticfiles import StaticFiles
+from sqlalchemy.exc import OperationalError, SQLAlchemyError
 from sqlalchemy import select
 from sqlalchemy.orm import Session
 
-from app.db import SessionLocal, get_db_session, init_db
+from app.db import SessionLocal, backup_sqlite_files, get_db_session, init_db
 from app.models import Comment, ContentItem, Hotspot, Report
 from app.schemas import CreateTaskRequest, CreateTaskResponse, TaskResponse
 from app.services.export_service import export_hotspot_comments_csv, export_item_comments_csv, export_report_markdown
@@ -24,6 +26,25 @@ from app.services.task_service import (
 from app.templating import templates
 
 
+logger = logging.getLogger(__name__)
+DATABASE_UNAVAILABLE_MESSAGE = "数据库暂时不可用，请稍后重试或联系维护者恢复数据。"
+
+
+def handle_database_error(request: Request, exc: SQLAlchemyError):
+    try:
+        backup_sqlite_files()
+    except Exception:
+        logger.exception("Failed to back up SQLite files after database error")
+    if request.url.path.startswith("/api/"):
+        return JSONResponse(status_code=503, content={"detail": DATABASE_UNAVAILABLE_MESSAGE})
+    return templates.TemplateResponse(
+        request,
+        "errors/database_unavailable.html",
+        {"message": DATABASE_UNAVAILABLE_MESSAGE, "detail": str(exc)},
+        status_code=503,
+    )
+
+
 @asynccontextmanager
 async def lifespan(_app: FastAPI) -> AsyncGenerator[None]:
     init_db()
@@ -36,6 +57,16 @@ app = FastAPI(title="热榜评论分析工具", lifespan=lifespan)
 app.mount("/static", StaticFiles(directory="app/static"), name="static")
 
 
+@app.exception_handler(OperationalError)
+def operational_error_handler(request: Request, exc: OperationalError):
+    return handle_database_error(request, exc)
+
+
+@app.exception_handler(SQLAlchemyError)
+def sqlalchemy_error_handler(request: Request, exc: SQLAlchemyError):
+    return handle_database_error(request, exc)
+
+
 @app.get("/health")
 def health() -> dict[str, str]:
     return {"status": "ok"}