Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the behavioral burden. 'Disposable' and 'from the Markdown vault' add useful context that the index is derived and reconstructable. However, it does not disclose whether the rebuild is destructive to the current index, whether it blocks, or any time/resource implications.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.