Ok, now I have a new seat molding (big thanks to BlackStridaAustria!)!
I have moved the saddle forward as much as possible to prevent such breaking in future.
Interestingly, strida manual does not provide tightening torque for regular (non-QR) seat molding saddle bolt, only for the QR one (25-35Nm), but I think that both are built from pretty much the same material, so I used 30Nm to tighten.
As for the knees clearance - I’ve inverted the eccentric bottom bracket as described here. Knees still touch handlebars, but don’t bump into them. So, it seems to be fine even with flat handlebars (will try those later).