Harvestman
The Harvestman is a large climbing mob that walks on walls and ceilings and can be ridden.
Riding is broken
Riding a harvestman is currently unreliable. The mount spins on ceilings and turning it is difficult. This is a regression and is being repaired.
Mechanism
Movement is driven by HarvestmanMoveControl over the climb net. Riding lives in climb/HarvestmanRiding.kt, which owns the seat position, the ridden tick, climb steering, the jump excursion and the landing settle. Three client hooks are installed by client/HarvestmanClient.kt from SporkClient: the seat provider, jump input and camera frame.
Rider yaw is taken from ClimbFrame.riddenAxisYaw and the rider's body rotation from ClimbFrame.riderBodyYaw, both in the surface frame rather than the world frame.