import { type Filter } from "https://dotland.deno.dev/x/grammy@v1.18.3/mod.ts";

This type infers which properties will be present on the given context object provided it matches the given filter query. If the filter query is a union type, the produced context object will be a union of possible combinations, hence allowing you to narrow down manually which of the properties are present.

In some sense, this type computes matchFilter on the type level.