Hey Kenny,
This is a good question. At the moment, because our React boilerplate doesn't use TypeScript by default, the TectonContext is declared in vanilla JavaScript. Since we can't use Type Annotations in plain JS/X, we are little limited at the time.
If you have already converted your codebase to use TypeScript, doing the following should get you what you want:
// frontend/src/contexts/tecton.ts
import { IActions, ISources } from "q2-tecton-sdk";
const TectonContext = createContext({
actions: {},
sources: {},
}, {actions: IActions, sources: ISources});