W0: terrain from worldlet building blocks (Valley in data/worldlets, identical heights), WorldInfo API, worldlet in saves and servers; the cliff tunnel plan

scripts/world/world.gd

@@ -895,6 +895,44 @@ func water_at(x: float, z: float) -> Dictionary:
 		return {"type": "sea", "surface": terrain.sea_level, "depth": terrain.sea_level - ground}
 	return {}
 
+# --- the worldlet (docs/WORLDLETS_DESIGN.md: the WorldInfo API) --------------------
+# What a system outside the terrain should ask about this place, rather than
+# reading the terrain's numbers: which worldlet it is, its water, its climate,
+# and its ways out. (W0 adds these; systems move over to them as each worldlet
+# needs them to be different.)
+
+## This worldlet's id ("valley") and its whole definition.
+func worldlet_id() -> String:
+	return terrain.worldlet_id
+
+func worldlet() -> Dictionary:
+	return terrain.worldlet
+
+## Its bodies of water: [{"type", "surface", "center" (x, z; the sea's is a
+## point on its coast), "radius" (a lake's; the sea's is 0)}].
+func water_bodies() -> Array:
+	var out: Array = []
+	for b in terrain._blocks:
+		match String(b.type):
+			"lake":
+				out.append({"type": "lake", "surface": terrain.water_level,
+					"center": terrain.lake_center, "radius": terrain.lake_radius})
+			"sea_cliff":
+				out.append({"type": "sea", "surface": terrain.sea_level,
+					"center": terrain.coast_point(terrain.sea_angle_deg, 20.0), "radius": 0.0})
+	return out
+
+## Its climate: {"snowline": m, ...} (more as worldlets differ).
+func climate() -> Dictionary:
+	var c: Dictionary = terrain.worldlet.get("climate", {}).duplicate()
+	c["snowline"] = terrain.snow_height
+	return c
+
+## Its ways on to other worldlets (the journey): [{"to", "by", "where"}].
+## Planned in the definition; travel comes with J1.
+func crossings() -> Array:
+	return terrain.worldlet.get("next", [])
+
 # --- multiplayer -----------------------------------------------------------------
 
 ## Joined a server: start where it says, follow its clock, show the others.