feat(world): ✨ Add new biome types (tundra, savanna) with temperature/humidity rules and enhance classification logic

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

engine/src/models/world/biome.gd

@@ -16,6 +16,7 @@ var flora_climax: Dictionary = {
 }  # target values at peak quality
 var fauna_capacity: int = 10  # max creatures per tile
 var food_web_tier: String = ""
+var tags: Array[String] = []  # semantic tags (is_water, is_elevated, etc.)
 
 
 static func from_dict(data: Dictionary) -> BiomeModel:
@@ -43,6 +44,9 @@ static func from_dict(data: Dictionary) -> BiomeModel:
 	b.flora_climax = data.get("flora_climax", {"canopy": 0.0, "undergrowth": 0.0, "fungi": 0.0})
 	b.fauna_capacity = data.get("fauna_capacity", 10)
 	b.food_web_tier = data.get("food_web_tier", "")
+	b.tags = []
+	for t: Variant in data.get("tags", []):
+		b.tags.append(String(t))
 	return b
 
 
@@ -57,4 +61,5 @@ func to_dict() -> Dictionary:
 		"flora_climax": flora_climax,
 		"fauna_capacity": fauna_capacity,
 		"food_web_tier": food_web_tier,
+		"tags": tags,
 	}

engine/src/models/world/biome_classifier.gd

@@ -29,6 +29,12 @@ static func classify(tile: Variant) -> String:
 ## Aquatic classification: water body type + temperature + depth.
 ## Falls back to biome_id when water_body_type is not set (TS guide tiles).
 static func _classify_aquatic(tile: Variant) -> String:
+	# Boil threshold: water-substrate tile too hot for liquid water → volcanic basin.
+	# Normalized temperature 0.82 ≈ 800°C surface temp — pre-ocean Hadean conditions.
+	const WATER_BOIL_TEMP: float = 0.82
+	if _get_temperature(tile) >= WATER_BOIL_TEMP:
+		return "volcanic"
+
 	var wb_type: String = _get_water_body_type(tile)
 	var biome: String = _get_biome_id(tile)
 
@@ -70,7 +76,7 @@ static func _classify_land(tile: Variant) -> String:
 
 	# Wetland override: saturated moisture on lowland
 	# (mangrove already handled in classify() before water/land split)
-	if moisture > 0.7 and elevation < 0.4:
+	if moisture > 0.7 and elevation < 0.4 and canopy > 0:
 		if temp > 0.4:
 			return "swamp"
 		return "bog"
@@ -78,36 +84,41 @@ static func _classify_land(tile: Variant) -> String:
 	# Elevation-driven
 	if elevation > 0.85:
 		if temp < 0.1:
-			return "permanent_ice"
+			return "glacial"
 		return "alpine_tundra"
 
 	if elevation > 0.70:
-		if moisture > 0.3:
+		if canopy > 0 and moisture > 0.3:
 			return "alpine_meadow"
 		return "alpine_tundra"
 
 	if elevation > 0.55:
 		if canopy > 0.4:
 			return "montane_forest"
-		if moisture > 0.7 and temp > 0.3:
+		if canopy > 0 and moisture > 0.7 and temp > 0.3:
 			return "cloud_forest"
-		return "alpine_meadow"
+		if canopy > 0 and moisture > 0.3:
+			return "alpine_meadow"
+		return "alpine_tundra"
 
 	# Temperature-driven (lowland/midland)
 	if temp > 0.55:
 		if moisture > 0.7 and canopy > 0.6:
 			return "tropical_rainforest"
-		if moisture > 0.4:
-			return "tropical_dry_forest"
-		if moisture > 0.2:
-			return "savanna"
+		# Without biology, warm moist land is bare rock — not savanna or dry forest
+		if canopy > 0:
+			if moisture > 0.4:
+				return "tropical_dry_forest"
+			if moisture > 0.2:
+				return "savanna"
 		return "desert"
 
 	# Temperate
 	if temp > 0.25:
 		if canopy > 0.5:
 			return "temperate_forest"
-		if moisture > 0.3:
+		# Without biology, temperate moist land is bare rock — not grassland
+		if moisture > 0.3 and canopy > 0:
 			return "temperate_grassland"
 		return "chaparral"
 
@@ -115,7 +126,9 @@ static func _classify_land(tile: Variant) -> String:
 	if temp > 0.1:
 		if canopy > 0.3:
 			return "boreal_forest"
-		return "tundra"
+		if canopy > 0:
+			return "tundra"
+		return "polar_desert"
 
 	return "polar_desert"