.tip

In most setups a regular import of an interface gets erased at compile time. That holds until a bundler or the isolatedModules flag needs to know without looking, and then it's either an error or a leftover runtime import.

import type { Post } from "./types";
import { format, type Options } from "./format";

Biome and the TypeScript compiler can both enforce it. It keeps the dependency graph honest too, since a type-only edge doesn't pull the module into the bundle.