> How do you import to a specific version?

Simply specify the version in the URL. For example, this URL fully specifies the code being run: https://unpkg.com/liltest@0.0.5/dist/liltest.js. Combined with the aforementioned technique of setting $DENO_DIR in production to stored code, one can fully specify the exact code being run, and execute the code without network access.

> It seems unwieldy to import URLs everywhere. What if one of the URLs links to a subtly different version of a library?

Isn't it error prone to maintain URLs everywhere in a large project? The solution is to import and re-export your external libraries in a central deps.ts file (which serves the same purpose as Node's package.json file). For example, let's say you were using the above assertion library across a large project. Rather than importing "https://deno.land/std/testing/asserts.ts" everywhere, you could create a deps.ts file that exports the third-party code.