Module tools 

The tools an agent may call, named once.

Why the registry is here rather than in the server

Prompts tell agents to call these tools. Before this existed, the names in prompts, in the book and in the code disagreed — eleven were documented and none were implemented — because nothing could check. A name is only useful if the thing answering to it exists.

Putting the list in the domain crate means layover validate can read a prompt, find every tool it mentions, and refuse a factory that tells an agent to call something that is not there. That check is worth more than it sounds: an agent instructed to use a tool it does not have will improvise, and improvising is exactly what a factory is meant not to do unattended.

What is deliberately absent

There is no layover_spawn. A mode = "spawn" route already opens one itinerary per flight, and a tool that did the same would be a second permission model over the same graph — two places to look when asking what an agent is allowed to start, which is one too many.

Enums

Tool

A tool an agent can call over MCP.

Functions

unknown_tools_in

Every layover_* name mentioned in text that is not a tool.