fix(ai): 🐛 update capital walls priority logic

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/game/engine/src/modules/ai/simple_heuristic_ai.gd

@@ -553,6 +553,20 @@ static func _decide_production(
 		if not rush_unit.is_empty():
 			return _prod_unit(city_index, rush_unit)
 
+	# Capital walls interject: non-threatened 1-city capital, >20 turns old,
+	# with at least 2 defenders gets walls slotted in before early_mil_floor
+	# and founders. Walls were previously starved by mil-floor then founder
+	# priorities, deferring walls indefinitely even when gold was plentiful.
+	var capital_age: int = GameState.turn_number - int(city.turn_founded)
+	var capital_needs_walls: bool = (
+		not threatened and city_count == 1 and city_index == 0
+		and military_count >= 2 and capital_age > 20
+		and not city.has_building("walls")
+		and city.can_build("walls", player)
+	)
+	if capital_needs_walls:
+		return _prod_building(city_index, "walls")
+
 	# Priority 0: Early military floor — maintain 4 warriors during the
 	# first 80 turns before committing to walls/happiness/founder. Early
 	# combat attrition (p0 harasses) was dropping mil to 1-2 by T75; this

src/simulator/crates/mc-ecology/src/engine.rs

@@ -1,4 +1,4 @@
-use std::collections::{BTreeMap, HashMap, HashSet};
+use std::collections::{BTreeMap, BTreeSet, HashMap};
 
 use mc_core::algorithms::hex;
 use mc_core::grid::GridState;