[vite] warning: Could not resolve import "#runtime/svelte/component/core"

I haven't seen this error before.

WelcomeAppShell.svelte

WelcomeAppShell.svelte

  import { ApplicationShell }   from '#runtime/svelte/component/core';

  import { ApplicationShell }   from '#runtime/svelte/component/core';

Foundry v12, developing a new system.

Any clues?

[vite] warning: Could not resolve import "#runtime/svelte/component/core" - TyphonJS