Ionic 4 + Stencil custom component: "error TS2304: Cannot find name"

My Stencil folder is part of the overall Ionic 4 app/project.
The Stencil part works flawless and produces a 100% correct components.d.ts file with global declarations, such as HTMLMyCustomCompElement.

Going by:

I should be able to use the components HTML* type in any part of the Ionic 4 app code, right?

vscode thinks it’s cool and shows no errors, in fact it shows proper linkage to components.d.ts when hovering over the type used in the app’s TS file.

Very different to ng which throws an error TS2304: Cannot find name - apparently it can’t find the type?!?

A bug? …or not sufficiently documented? …am I missing something?