docs: Update docstring to be more accurate

Author: anubhav756

packages/toolbox-core/src/toolbox_core/tool.py

@@ -64,7 +64,7 @@ def __init__(
             description: The description of the remote tool.
             params: The args of the tool.
             required_authn_params: A dict of required authenticated parameters to a list
-                of services that provide values for them.
+                of alternative services that can provide values for them.
             auth_service_token_getters: A dict of authService -> token (or callables that
                 produce a token)
             bound_params: A mapping of parameter names to bind to specific values or
@@ -288,6 +288,11 @@ def bind_parameters(
         """
         param_names = set(p.name for p in self.__params)
         for name in bound_params.keys():
+            if name in self.__bound_parameters:
+                raise ValueError(
+                    f"cannot re-bind parameter: parameter '{name}' is already bound"
+                )
+
             if name not in param_names:
                 raise Exception(f"unable to bind parameters: no parameter named {name}")