diff --git a/src/game/engine/src/modules/empire/happiness.gd b/src/game/engine/src/modules/empire/happiness.gd
index 542852e0..5ab2e806 100644
--- a/src/game/engine/src/modules/empire/happiness.gd
+++ b/src/game/engine/src/modules/empire/happiness.gd
@@ -60,7 +60,12 @@ static func process_turn(player: RefCounted, _game_map: RefCounted) -> void:
 	var ascension_active: bool = bool(player.ascension_active)
 	var growth_tier: String = player.growth_tier if player.growth_tier != "" else "balanced"
 
-	var unique_luxuries: int = _count_unique_luxuries(player, _game_map)
+	# Collect the set of distinct luxury resource IDs accessible to this
+	# player. The Rust side expects `owned_luxuries: BTreeSet<String>` and
+	# sums per-resource happiness_per_unique_copy values. Previously this
+	# was `unique_luxury_count: i32` — rename and payload shape both changed
+	# when luxury happiness moved from a flat count to a per-resource lookup.
+	var owned_luxuries: Array[String] = _collect_unique_luxury_ids(player, _game_map)
 
 	var input_dict: Dictionary = {
 		"city_count": player.cities.size(),
@@ -68,7 +73,7 @@ static func process_turn(player: RefCounted, _game_map: RefCounted) -> void:
 		"units_in_enemy_territory": units_in_enemy_territory,
 		"ascension_active": ascension_active,
 		"building_happiness": building_happiness,
-		"unique_luxury_count": unique_luxuries,
+		"owned_luxuries": owned_luxuries,
 		"growth_tier": growth_tier,
 	}
 
@@ -127,11 +132,15 @@ const LUXURY_DEPOSITS: Array[String] = [
 ]
 
 
-static func _count_unique_luxuries(player: RefCounted, game_map: RefCounted) -> int:
-	## Count unique luxury resources on tiles owned by the player's cities.
+static func _collect_unique_luxury_ids(player: RefCounted, game_map: RefCounted) -> Array[String]:
+	## Collect the set of distinct luxury resource IDs accessible to the
+	## player via owned tiles. Returns a sorted Array[String] suitable for
+	## JSON-serialising to Rust's `BTreeSet<String>` (sorted order preserves
+	## determinism across runs).
+	var result: Array[String] = []
 	if game_map == null:
-		return 0
-	var found: Dictionary = {}  # resource_id → true
+		return result
+	var found: Dictionary = {}  # resource_id → true (dedupe)
 	for city: Variant in player.cities:
 		for tile_pos: Vector2i in city.owned_tiles:
 			var tile: Resource = game_map.get_tile(tile_pos)
@@ -139,7 +148,11 @@ static func _count_unique_luxuries(player: RefCounted, game_map: RefCounted) ->
 				continue
 			if tile.resource_id in LUXURY_DEPOSITS and tile.resource_id not in found:
 				found[tile.resource_id] = true
-	return found.size()
+	var ids: Array = found.keys()
+	ids.sort()
+	for id_: Variant in ids:
+		result.append(String(id_))
+	return result
 
 
 static func _count_units_in_enemy_territory(player: RefCounted) -> int: