File to use when typing new store properties

[Viicos]

I have followed the following #1092 (comment) to add the router as a property on my store, and I'm trying to use https://pinia.vuejs.org/core-concepts/plugins.html#typing-new-store-properties so that Typescript doesn't complain.

I've created a pinia.d.ts file containing the custom PiniaCustomProperties extension, but then TS (or my IDE, VSCode) doesn't seem to know anything about pinia anymore: