MountSeat
Represents a single seat on a mount-point bone.
Uses an Interaction entity (1.19.4+) as the vehicle. Interaction has no model on either Java or Bedrock by design, which bypasses Geyser's armor-stand renderer entirely — that renderer continued to draw the seat for Bedrock viewers no matter which Java-side visibility flag was set (setVisible, setInvisible, marker, hideEntity all proven ineffective for the rider-vehicle case).