Looks like using Svelte via import maps got a lot more gnarly between v4 and v5, unfortunately.
(via https://generator.jspm.io/)
{ "imports": { "svelte": "https://unpkg.com/svelte@4.2.19/src/runtime/index.js" } } "> 
{ "imports": { "svelte": "https://unpkg.com/svelte@5.19.10/src/index-client.js" }, "scopes": { "https://unpkg.com/": { "clsx": "https://unpkg.com/clsx@2.1.1/dist/clsx.mjs", "esm-env": "https://unpkg.com/esm-env@1.2.2/index.js", "esm-env/browser": "https://unpkg.com/esm-env@1.2.2/true.js", "esm-env/development": "https://unpkg.com/esm-env@1.2.2/false.js", "esm-env/node": "https://unpkg.com/esm-env@1.2.2/false.js" } } } ">