- A messenger's `registerActionHandler` slot typed `(...args: any[]) => any`: it receives strongly-typed handler callbacks inward at registration _and_ is invoked with strongly-typed argument tuples outward at dispatch. `unknown[]` fails registration; `never[]` fails dispatch.
- A `coerces` map sitting between a library signature and a caller's own config — see [`metamask-extension#41104 (r3045807022)`](https://github.com/MetaMask/metamask-extension/pull/41104#discussion_r3045807022).
Originally posted by @MajorLift in MetaMask/contributor-docs#170 (comment)