Deno already analyzes the entire module graph before the application starts up, so we extract out the npm specifiers ahead of time, do the npm dependency analysis, cache any packages as needed, then start execution.
We'll have custom registry support. For local npm packages, that would be nice to have, but probably something that will be implemented later. It could actually be done in a hacky way with the existing implementation of this we have, but it would be better to have something specifically designed for this.