ludic.npc (18.2): a person a crowd moves

npc_set_crowd hands a person to a crowd. Its walk no longer steps or asks the way: its want is goal_x / goal_z / goal_speed (0 when it is not walking). npc_moved hands back the crowd's place: position, ground, heading from velocity, gait. Arrival, the act and the give-up after twenty seconds without progress are unchanged. Nothing allocates. npc 16/16.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.npc/way.ludic

@@ -56,3 +56,21 @@ function np_stuck(npc_st: mut NpcState, p: NpcPerson) -> void {
     npc_plan(npc_st, p)
   }
 }
+
+# the crowd's side (phase 18): a crowd walker says where it is going and how fast, and is handed
+# back where the crowd put it; nothing allocates, since this runs for every walker every frame
+function np_crowd_want(p: NpcPerson, speed: float) -> void {
+  p.goal_x = p.tx
+  p.goal_z = p.tz
+  p.goal_speed = speed
+}
+export function npc_set_crowd(p: NpcPerson, on: bool) -> void { p.crowd = on }
+export function npc_moved(p: NpcPerson, x: float, z: float, vx: float, vz: float) -> void {
+  let dx = x - p.x
+  let dz = z - p.z
+  p.x = x
+  p.z = z
+  p.y = NpcWorld.ground(x, z)
+  if vx * vx + vz * vz > 0.01 { p.yaw = Math.atan2(-vx, -vz) }
+  p.phase = p.phase + Math.sqrt(dx * dx + dz * dz) * 2.6
+}