perf(*): bound list queries, batch fetches, harden media downloads

backend/src/userbot/modules/jobs/handlers/fetch_media.py

@@ -18,6 +18,10 @@ async def fetch_media(ctx: JobContext) -> None:
     if isinstance(message, list):
         message = message[0] if message else None
     if message is None or message.empty:
-        return
+        msg = f"message {chat_id}/{message_id} is unavailable"
+        raise RuntimeError(msg)
     toggles = CaptureToggles(media=True, self_destruct_media=True)
-    await capture_media(client, message, capture, chat_id, message_id, toggles)
+    ok = await capture_media(client, message, capture, chat_id, message_id, toggles)
+    if not ok:
+        msg = f"media download failed for {chat_id}/{message_id}"
+        raise RuntimeError(msg)