For agents, on top of README.md, which they read first.

Notes for agents

Depend on serde only. This crate is compiled into the mod's JavaScript; anything that needs an OS breaks just mod.

A change here is a change to both sides. Rebuild the mod (just mod, commit plugin/hooks/jevhooks.js) and the daemon (just daemon) together, and update plugin/types/index.d.ts if Decision changed.