[alexlarsson]

Runtimes are not package dependencies. They are not separated from the app to allow dependency resolution. They are separated out in order to allow a different entity to maintain and update them. The idea is that they are pretty minimal (to some degree) and come with a well defined ABI and stability/lifetime guarantee.

If, above this, you need more dependencies, in the flatpak model you need to bundle them yourself. Such bundling can be done however you want. For instance you can reuse existing packages from some distro, you can build the yourselves, or whatever.

Technically you have to specify a runtime, or things will not run. But if you want you can create your own runtime that is empty and use that. This means you have to supply everything though, as you won't even have an ld.so.