Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description does disclose the key state change: the session corpus is discarded and discovery mode reverts to cwd/config. It does not say whether closing an already-closed corpus is an error, whether the corpus state is recoverable, or what is returned, which matters for a state-clearing operation.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.