As a higher-level alternative to bwrap, I sometimes use `flatpak run --filesystem=$PWD --command=bash org.freedesktop.Platform`. This is kind of an abuse of flatpaks but works just fine to make a sandbox. And unlike bwrap, it has sane defaults (no extra permissions, not even network, though it does allow xdg-desktop-portal).
To be honest - and I can't really believe I'm saying it - what I really want is something more like Android permissions. (Except more granular file permissions, which Android doesn't do at all well.) Like: start with nothing, app is requesting x access, allow it this time; oh alright fine always allow it. Central place to manage it later. Etc.
Maybe I misunderstood this point. But the ssh socket also gives access to your private keys, so I see no security gain in that point. Better to have a password protected key.