fix: protect retained canonical assets from cleanup

app/services/cleanup.py

@@ -129,16 +129,17 @@ class CleanupService:
             raise NotFoundError("Output file not found")
         return candidate
 
-    async def cleanup_expired(self) -> int:
+    async def cleanup_expired(self, protected_request_ids: set[str] | None = None) -> int:
         cutoff = time.time() - self.settings.cleanup_minutes * 60
         async with self._lock:
             active = self._active.copy()
         removed = 0
+        protected = protected_request_ids or set()
         for base in (self.settings.temp_dir, self.settings.output_dir):
             if not base.exists():
                 continue
             for path in list(base.iterdir()):
-                if not path.is_dir() or path.name in active:
+                if not path.is_dir() or path.name in active or path.name in protected:
                     continue
                 try:
                     if path.stat().st_mtime < cutoff: