Tightly couple indexing of online metadata
Currently the out-of-process miners (from gnome-online-miners), used to index and cache the metadata of remote content, are accessed as D-Bus session services. It was done this way because consuming D-Bus session services is so easy.
However, this is wrong because the miners aren't intended to be services shipped by the operating system. They are part of the application and often need to be updated in lock step. eg., the API offered by the miners doesn't have any promise of stability. Fortunately, this hasn't been a problem so far because applications were shipped as part of the OS and the distributor ensured that the versions matched.
It is now a problem with Flatpak, though. The Flatpak-ed application is decoupled from the OS, and one can't expect them to have matching versions. In such a scenario, the miners should be used as private helpers and bundled with the application. Peer-to-peer D-Bus, like we use for the thumbnailer, is a good option instead of the hub-and-spoke session D-Bus.
This needs to be solved before we can enable online content in the Flatpak-ed builds. Otherwise things won't reliably work and break in subtle ways.