Fix mount movement jitter by following vanilla horse/boat sync pattern

- 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.

src/main/java/noppes/npcs/entity/EntityNPCFlying.java

@@ -84,7 +84,6 @@ public abstract class EntityNPCFlying extends EntityNPCInterface {
         }
 
         this.updateLimbSwing();
-        this.velocityChanged = true;
     }
 
     public void updateLimbSwing() {
@@ -136,7 +135,6 @@ public abstract class EntityNPCFlying extends EntityNPCInterface {
 
         if (flightModeActive) {
             super.performMountedMovement(strafe, forward, moveSpeed);
-            this.velocityChanged = true;
             return;
         }
 
@@ -149,6 +147,5 @@ public abstract class EntityNPCFlying extends EntityNPCInterface {
         }
 
         this.updateLimbSwing();
-        this.velocityChanged = true;
     }
 }

src/main/java/noppes/npcs/entity/EntityNPCInterface.java

@@ -2130,35 +2130,21 @@ public abstract class EntityNPCInterface extends EntityCreature implements IEnti
         this.moveForward = forward;
 
         boolean flightMode = isMountFlightModeActive();
-        double prevMotionX = this.motionX;
         double prevMotionY = this.motionY;
-        double prevMotionZ = this.motionZ;
-        float previousJumpFactor = this.jumpMovementFactor;
-        float appliedJumpFactor = getMountedAirStrafeFactor(moveSpeed, flightMode);
-
-        this.jumpMovementFactor = appliedJumpFactor;
-
-        this.setAIMoveSpeed(moveSpeed);
-
-        super.moveEntityWithHeading(strafe, forward);
-
-        if (flightMode) {
-            this.motionY = prevMotionY;
-            this.isAirBorne = true;
-        }
-
-        this.jumpMovementFactor = previousJumpFactor;
 
+        // Server-side only physics (like vanilla horse)
         if (!worldObj.isRemote) {
-            double newMotionX = this.motionX;
-            double newMotionY = this.motionY;
-            double newMotionZ = this.motionZ;
-            if (Math.abs(newMotionX - prevMotionX) > 1.0E-5D || Math.abs(newMotionY - prevMotionY) > 1.0E-5D || Math.abs(newMotionZ - prevMotionZ) > 1.0E-5D) {
-                this.velocityChanged = true;
+            this.jumpMovementFactor = getMountedAirStrafeFactor(moveSpeed, flightMode);
+            this.setAIMoveSpeed(moveSpeed);
+            super.moveEntityWithHeading(strafe, forward);
+
+            if (flightMode) {
+                this.motionY = prevMotionY;
+                this.isAirBorne = true;
             }
         }
 
-        syncMountedRiderVelocity();
+        // Both sides do animation (like vanilla horse)
         updateMountedLimbSwing();
     }
 
@@ -2176,28 +2162,6 @@ public abstract class EntityNPCInterface extends EntityCreature implements IEnti
         return moveSpeed * 0.5F;
     }
 
-    private void syncMountedRiderVelocity() {
-        if (!(this.riddenByEntity instanceof EntityLivingBase)) {
-            return;
-        }
-        EntityLivingBase rider = (EntityLivingBase) this.riddenByEntity;
-        double riderPrevMotionX = rider.motionX;
-        double riderPrevMotionY = rider.motionY;
-        double riderPrevMotionZ = rider.motionZ;
-
-        rider.motionX = this.motionX;
-        rider.motionY = this.motionY;
-        rider.motionZ = this.motionZ;
-        rider.fallDistance = 0.0F;
-        rider.isAirBorne = !this.onGround;
-
-        if (!worldObj.isRemote) {
-            if (Math.abs(rider.motionX - riderPrevMotionX) > 1.0E-5D || Math.abs(rider.motionY - riderPrevMotionY) > 1.0E-5D || Math.abs(rider.motionZ - riderPrevMotionZ) > 1.0E-5D) {
-                rider.velocityChanged = true;
-            }
-        }
-    }
-
     private void updateMountedLimbSwing() {
         this.prevLimbSwingAmount = this.limbSwingAmount;
         double deltaX = this.posX - this.prevPosX;

src/main/java/noppes/npcs/util/NPCMountUtil.java

@@ -122,49 +122,22 @@ public final class NPCMountUtil {
                 npc.isAirBorne = true;
                 npc.fallDistance = 0.0F;
 
-                if (!npc.worldObj.isRemote && Math.abs(previousMotionY - newMotionY) > 1.0E-4D) {
-                    npc.velocityChanged = true;
-                }
-
-                if (!npc.worldObj.isRemote && rider instanceof EntityPlayer) {
-                    EntityPlayer player = (EntityPlayer) rider;
-                    if (!player.capabilities.isFlying) {
-                        double playerPrevMotion = player.motionY;
-                        player.motionY = npc.motionY;
-                        if (Math.abs(playerPrevMotion - player.motionY) > 1.0E-4D) {
-                            player.velocityChanged = true;
-                        }
-                    }
-                }
                 return;
             }
 
             if (jumpPressed && npc.onGround) {
-                double previousMotionY = npc.motionY;
                 npc.motionY = jumpFactor;
                 npc.setNpcJumpingState(true);
                 npc.isAirBorne = true;
                 npc.fallDistance = 0.0F;
                 if (!npc.worldObj.isRemote) {
-                    if (Math.abs(previousMotionY - npc.motionY) > 1.0E-4D) {
-                        npc.velocityChanged = true;
-                    }
                     net.minecraftforge.common.ForgeHooks.onLivingJump(npc);
                 }
                 return;
             }
 
             if (!npc.onGround) {
-                double previousMotionY = npc.motionY;
-                double limitedMotionY = Math.max(npc.motionY, -descendSpeed);
-                if (Math.abs(previousMotionY - limitedMotionY) > 1.0E-4D) {
-                    npc.motionY = limitedMotionY;
-                    if (!npc.worldObj.isRemote) {
-                        npc.velocityChanged = true;
-                    }
-                } else {
-                    npc.motionY = limitedMotionY;
-                }
+                npc.motionY = Math.max(npc.motionY, -descendSpeed);
                 npc.setNpcFlyingState(!npc.isInWater());
             } else {
                 npc.setNpcFlyingState(false);
@@ -174,20 +147,14 @@ public final class NPCMountUtil {
         }
 
         if (npc.onGround) {
-            double previousMotionY = npc.motionY;
             if (rider.isJumping) {
                 npc.motionY = jumpFactor;
                 npc.setNpcJumpingState(true);
                 npc.isAirBorne = true;
                 npc.fallDistance = 0.0F;
                 if (!npc.worldObj.isRemote) {
-                    if (Math.abs(previousMotionY - npc.motionY) > 1.0E-4D) {
-                        npc.velocityChanged = true;
-                    }
                     net.minecraftforge.common.ForgeHooks.onLivingJump(npc);
                 }
-            } else {
-                npc.motionY = 0.0D;
             }
             return;
         }
@@ -239,9 +206,6 @@ public final class NPCMountUtil {
     }
 
     public static void haltMountedMotion(EntityNPCInterface npc, MountState state) {
-        double prevMotionX = npc.motionX;
-        double prevMotionY = npc.motionY;
-        double prevMotionZ = npc.motionZ;
         npc.motionX = 0.0D;
         npc.motionY = 0.0D;
         npc.motionZ = 0.0D;
@@ -254,9 +218,6 @@ public final class NPCMountUtil {
         npc.limbSwing = 0.0F;
         npc.getNavigator().clearPathEntity();
         npc.fallDistance = 0.0F;
-        if (!npc.worldObj.isRemote && (Math.abs(prevMotionX) > 1.0E-4D || Math.abs(prevMotionY) > 1.0E-4D || Math.abs(prevMotionZ) > 1.0E-4D)) {
-            npc.velocityChanged = true;
-        }
         resetMountedFlightState(npc, state);
     }
 
@@ -283,16 +244,11 @@ public final class NPCMountUtil {
             return;
         }
 
-        double desired = -descendSpeed;
-        double previousMotionY = npc.motionY;
-        npc.motionY = desired;
+        npc.motionY = -descendSpeed;
         npc.isAirBorne = true;
         npc.fallDistance = 0.0F;
         npc.setNpcFlyingState(true);
         npc.setNpcJumpingState(false);
-        if (!npc.worldObj.isRemote && Math.abs(previousMotionY - desired) > 1.0E-4D) {
-            npc.velocityChanged = true;
-        }
     }
 
     public static void stabilizeDismountedRider(Entity rider) {
@@ -314,8 +270,6 @@ public final class NPCMountUtil {
             rider.motionZ = previousMotionZ;
             rider.fallDistance = previousFall;
         }
-
-        rider.velocityChanged = true;
     }
 
     private static void updateMountedFlightState(EntityNPCInterface npc, MountState state, RoleMount mount, EntityPlayer rider) {