refactor: restrict the scope of `USER_PERMISSIONS_CHAT_DELETION`

it can easily confuse people before becuase when people accidentally set `env.USER_PERMISSIONS_CHAT_DELETION` to `true/yes/Yes`, `USER_PERMISSIONS["chat"]["deletion"]` would become `False`, which is unexpectedly and hard to notice.

backend/config.py

@@ -289,8 +289,12 @@ DEFAULT_PROMPT_SUGGESTIONS = (
 
 DEFAULT_USER_ROLE = os.getenv("DEFAULT_USER_ROLE", "pending")
 
-USER_PERMISSIONS_CHAT_DELETION = os.getenv('USER_PERMISSIONS_CHAT_DELETION', 'True') == 'True'
-USER_PERMISSIONS = {"chat": {"deletion": USER_PERMISSIONS_CHAT_DELETION}}
+USER_PERMISSIONS_CHAT_DELETION = os.getenv('USER_PERMISSIONS_CHAT_DELETION', 'True')
+
+if USER_PERMISSIONS_CHAT_DELETION not in ('True', 'False'):
+    raise ValueError(ERROR_MESSAGES.INCORRECT_FORMAT("  (e.g., True/False)."))
+
+USER_PERMISSIONS = {"chat": {"deletion": USER_PERMISSIONS_CHAT_DELETION == 'True'}}
 
 
 MODEL_FILTER_ENABLED = os.environ.get("MODEL_FILTER_ENABLED", False)

backend/constants.py

@@ -46,7 +46,7 @@ class ERROR_MESSAGES(str, Enum):
 
     PANDOC_NOT_INSTALLED = "Pandoc is not installed on the server. Please contact your administrator for assistance."
     INCORRECT_FORMAT = (
-        lambda err="": f"Invalid format. Please use the correct format{err if err else ''}"
+        lambda err="": f"Invalid format. Please use the correct format{err}"
     )
     RATE_LIMIT_EXCEEDED = "API rate limit exceeded"