Hatch a ghastling with its own setup, not an adult's

DriedGhastBlock.spawnGhastling calls setBaby(true) before addFreshEntity.
AgeableMob.setBaby -> setAge crosses the age boundary there, so
HappyGhast.ageBoundaryReached runs babyGhastSetup while the mob is still
being hatched: its box, its flying navigation and its brain are a
ghastling's before it joins the level.

Horizon's hatch path wrote extra.age directly after spawn_mob had already
registered the adult's goals (HappyGhastFloat, the tempt goal,
FloatAround) with a ground navigation and the brain stopped, so the
ghastling spent its first tick flying adult goals and only its first
aiStep (ensure_setup) corrected that. age_boundary_reached also had no
HappyGhast arm, so the crossing ran nothing for it at all.

The hatch now goes through finalize::set_age, which dispatches the
crossing to happy_ghast::ensure_setup like the other ageable species'
ageBoundaryReached arms.

The port_map row for HappyGhast.ageBoundaryReached named ensure_setup
without the dispatch that reaches it; it now points at the dispatch.

crates/horizon-client/src/game/ghasts.rs

@@ -155,7 +155,12 @@ impl Game<'_> {
         if let Some(id) = self.spawn_mob("minecraft:happy_ghast", at, true)
             && let Some(m) = self.mobs.iter_mut().find(|m| m.id == id)
         {
-            m.extra.age = -24000;
+            // DriedGhastBlock.spawnGhastling sets the baby age before
+            // addFreshEntity, so ageBoundaryReached runs the ghastling setup
+            // (`babyGhastSetup`) while the mob is still being hatched: its
+            // goals, navigation and brain are a ghastling's before its first
+            // tick, not an adult's until the next aiStep.
+            horizon_client::mobs::finalize::set_age(m, -24000);
             m.yaw = yaw;
             m.body_yaw = yaw;
             m.head_yaw = yaw;

crates/horizon-client/src/mobs/finalize.rs

@@ -863,6 +863,11 @@ fn age_boundary_reached(m: &mut Mob) {
         Species::Goat => set_base(m, Attr::AttackDamage, if baby { 1.0 } else { 2.0 }),
         Species::Hoglin => set_base(m, Attr::AttackDamage, if baby { 0.5 } else { 6.0 }),
         Species::SulfurCube if !baby => sulfur_size(m, 2),
+        // HappyGhast.ageBoundaryReached: adultGhastSetup or babyGhastSetup,
+        // then Animal's no-op. A hatched ghastling needs it before it is in
+        // the level (DriedGhastBlock.spawnGhastling sets the baby age before
+        // addFreshEntity), or its first tick flies the adult goals.
+        Species::HappyGhast => super::happy_ghast::ensure_setup(m),
         _ => {}
     }
 }

crates/horizon-client/src/mobs/happy_ghast.rs

@@ -667,4 +667,40 @@ mod tests {
     fn travel_speed_is_five_thirds_of_the_flying_speed() {
         assert!((f64::from(AIR_SPEED) - FLYING_SPEED * 5.0 / 3.0).abs() < 1e-7);
     }
+
+    /// `HappyGhast.ageBoundaryReached` runs the setup at the age crossing, not
+    /// at the next tick: `DriedGhastBlock.spawnGhastling` makes its ghastling a
+    /// baby before `addFreshEntity`, and `AgeableMob.setAge` calls
+    /// `ageBoundaryReached` there. Without it the hatched ghastling joins the
+    /// level with the adult's three goals, its ground navigation and its brain
+    /// stopped, and only its first `aiStep` (`ensure_setup`) fixes that.
+    #[test]
+    fn a_hatched_ghastling_is_set_up_as_one_at_the_age_crossing() {
+        use crate::mobs::Species;
+        let mut t = (*crate::mobs::sensor_scan_tests::kind()).clone();
+        t.species = Species::HappyGhast;
+        let mut m = Mob::new(
+            1,
+            std::sync::Arc::new(t),
+            horizon_core::geometry::Vec3::ZERO,
+            0.0,
+        );
+        // `Mob::new` registers the adult's goals (HappyGhastFloat, its tempt
+        // goal and FloatAround) for the age-zero ghast it makes.
+        assert_eq!(m.extra.scratch[0], 2, "an adult's setup at construction");
+        assert!(m.ai.goals.has("HappyGhastFloatGoal"));
+
+        crate::mobs::finalize::set_age(&mut m, -24000);
+
+        assert!(m.is_baby());
+        assert_eq!(m.extra.scratch[0], 1, "babyGhastSetup ran");
+        assert!(
+            !m.ai.goals.has("HappyGhastFloatGoal")
+                && !m.ai.goals.has("RandomFloatAroundGoal")
+                && !m.ai.goals.has("ForNonPathfinders"),
+            "a ghastling has no goals: its brain drives it"
+        );
+        assert_eq!(m.ai.nav.kind, crate::mobs::nav::NavKind::Flying);
+        assert!(m.ai.nav.can_float);
+    }
 }

tools/port_map/game-012.tsv

@@ -115,7 +115,7 @@ HappyGhast.setServerStillTimeout	inline	crates/horizon-client/src/mobs/happy_gha
 HappyGhast.registerGoals	port	crates/horizon-client/src/mobs/happy_ghast.rs::setup	adult goals: float, tempt (harness and food for a bare adult, food otherwise), float around within 16
 HappyGhast.adultGhastSetup	port	crates/horizon-client/src/mobs/happy_ghast.rs::setup	adult half: ghast move control, happy ghast look control, goals, brain stopped
 HappyGhast.babyGhastSetup	port	crates/horizon-client/src/mobs/happy_ghast.rs::setup	baby half: flying move control, baby flying navigation, no goals, timeout cleared
-HappyGhast.ageBoundaryReached	port	crates/horizon-client/src/mobs/happy_ghast.rs::ensure_setup	reruns setup when the age sign changes
+HappyGhast.ageBoundaryReached	port	crates/horizon-client/src/mobs/finalize.rs::age_boundary_reached	reruns the setup (happy_ghast::ensure_setup) when the age sign changes, so a hatched ghastling flies its own goals before its first tick
 HappyGhast.createAttributes	skip:data		attributes come from entity-types.json
 HappyGhast.getAmbientSoundInterval	port	crates/horizon-client/src/mobs.rs::Mob::ambient_interval	six times as long while it carries a rider
 HappyGhast.canUseSlot	inline	crates/horizon-client/src/game/ghasts.rs::Game::interact_happy_ghast	a harness goes only on a living adult without one; shears take it off