soup: SoupSession is not thread-safe but shared between element instances
This means that at least with libsoup3 we can't share the session between element instances anymore like this. We would lose connection and cookie sharing at least.
We should probably either move away from libsoup (to...?) or share not just the session between elements but a whole thread plus main context, and dispatch all operations via that main context so the session is only used from a single thread.
Not sure if this should be marked as blocker but AFAIU it's a regression compared to using
souphttpsrc with libsoup2.