- Remove all velocityChanged=true flags from mount movement code
(NPCMountUtil, EntityNPCInterface, EntityNPCFlying)
- Make performMountedMovement physics server-side only like vanilla horse
- Remove syncMountedRiderVelocity method that forced rider velocity packets
- Fix ground movement to not reset motionY every tick
- Let Minecraft's entity tracker handle position sync naturally
The jitter was caused by S12PacketEntityVelocity being sent every tick,
which constantly reset client interpolation. Vanilla horses/boats never
set velocityChanged and rely on the entity tracker for smooth sync.
Claude