fix: burn file items after download, not metadata fetch

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/api/public.py

@@ -1,8 +1,11 @@
 from fastapi import APIRouter, Depends, File, Form, HTTPException, Query, Request, UploadFile
 from fastapi.responses import FileResponse
 from sqlalchemy.orm import Session
+from starlette.background import BackgroundTask
 
+from app import db as db_module
 from app.db import get_db
+from app.models import Item
 from app.schemas import ItemCreate, ItemOut, TTLOption, WallResponse
 from app.services import items as items_service
 from app.services import storage as storage_service
@@ -72,6 +75,16 @@ def wall(
     )
 
 
+def _burn_file_after_response(item_id: int) -> None:
+    db = db_module.SessionLocal()
+    try:
+        item = db.get(Item, item_id)
+        if item is not None and item.burn_after_read and not item.burned:
+            items_service.burn_file_item(db, item)
+    finally:
+        db.close()
+
+
 @router.get("/{slug}/file")
 def download_file(slug: str, db: Session = Depends(get_db)):
     item = items_service.get_file_item(db, slug)
@@ -84,11 +97,15 @@ def download_file(slug: str, db: Session = Depends(get_db)):
     media_type = item.mime or "application/octet-stream"
     filename = item.file_name or path.name
     inline = media_type.startswith(_INLINE_IMAGE_PREFIXES)
+    background = None
+    if item.burn_after_read:
+        background = BackgroundTask(_burn_file_after_response, item.id)
     return FileResponse(
         path,
         media_type=media_type,
         filename=filename,
         content_disposition_type="inline" if inline else "attachment",
+        background=background,
     )