Action schemas for the messages tool. The notes surface through the help tool and are the worker-facing contract: what a handle and a thread are, what a check takes away and a read does not, and how a page ends.

The body carries no maxLength: the cap is in bytes, and the context refuses an oversized body with where to put the content instead. A handle or a thread name carries one of 128 characters; the context refuses one over 512 bytes, which no name the gate lets through reaches, for a call that never meets the gate.