declarationMap sources not following src filename

Describe the bug

When using SvelteKit with TypeScript declaration maps enabled, the generated .d.ts files for .svelte components correctly include a .d.ts.map file.
However, IDEs like VSCode do not follow the .d.ts.map back to the original .svelte source, even though the map exists and points to the right file.

This breaks TypeScript navigation (“Go to definition”) and makes debugging or inspection of Svelte component types harder.

Reproduction

Open this minimal reproduction:
👉 StackBlitz – SvelteKit declarationMap issue reproduction

Build the Svelte component to generate .d.ts and .d.ts.map.

In an editor (e.g. VSCode), Ctrl/Cmd + click on the imported component.

Logs

System Info

System:
    OS: Linux 6.8 Ubuntu 24.04.3 LTS 24.04.3 LTS (Noble Numbat)
    CPU: (8) x64 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz
    Memory: 11.41 GB / 31.07 GB
    Shell: 5.9
  Binaries:
    Node: 22.14.0 
    npm: 10.9.2
    pnpm: 10.14.0 
  Browsers:
    Chrome: 141.0.7390.65

Severity

annoyance

Additional Information

Actual

{"version":3,"file":"Toto.svelte.d.ts","sourceRoot":"","sources":["../src/lib/Toto.svelte.ts"],

Expected

{"version":3,"file":"Toto.svelte.d.ts","sourceRoot":"","sources":["../src/lib/Toto.svelte"],

Run the linked StackBlitz reproduction and build the component to inspect dist/Toto.svelte.d.ts.map. Compare its sources entry with the reported actual and expected paths, including src/lib/Toto.svelte.ts and src/lib/Toto.svelte; done means editors can follow the declaration map to the .svelte source.