Under the hood
MCP poll_event now rejects malformed kind values, not just reserved names
What
The MCP (Model Context Protocol, the standard Claude Code uses to talk to external tools) poll_event control request now validates the format of the kind value it's given before checking whether that name is reserved. A valid kind must start with a lowercase letter and contain only lowercase letters, digits, and hyphens after that, up to 64 characters. The wording used when a kind is rejected as reserved has also changed.
Why
This catches malformed event kinds earlier and more clearly, rather than only rejecting names that happen to collide with reserved ones.