qunitx run was pointed at a file that is not there.

Checked here rather than left to esbuild: the entry is reached through a generated import(...), and esbuild treats an unresolvable DYNAMIC import as a warning, leaving it in the bundle as a runtime fetch. The browser then 404s and reports "failed to load dynamically imported module", which names the bundler's URL instead of the user's typo.

import { ScriptNotFound } from './run.ts';

ScriptNotFound({ entry: '/proj/seed.ts' }).message; // 'no such script: /proj/seed.ts'