test: browser suite flake 'Failed to fetch dynamically imported module' on a test file during test:full #640

Seen in the 4.6.0 release run (test:full, components): src/lib/forms/PhoneField.svelte.test.ts failed to import with TypeError: Failed to fetch dynamically imported module (Vite browser server). All 2188 tests passed; the file passes alone (9/9). No optimizer reload is logged. It happened while the site build ran in parallel with the components (#617 overlap). Likely cause: a Vite server-side transform or a request timeout under load. Needs a reproducer: the full suite under the same overlap, repeatedly.