diff --git a/scripts/chunk.gd b/scripts/chunk.gd
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+class_name Chunk
+extends Node2D
+## A single loaded chunk in the world.
+##
+## A chunk is a fixed-size, axis-aligned region of a room. It is the atomic
+## unit of load, save, and stream. This node is instantiated by the
+## [ChunkStreamer] when a chunk is loaded from the server and freed when the
+## chunk is unloaded.
+
+## World-space size of a chunk along X (world units / tiles).
+const CHUNK_SIZE_X := 32.0
+## World-space size of a chunk along Y (world units / tiles).
+const CHUNK_SIZE_Y := 32.0
+## World-space size of a chunk along Z (world units / tiles).
+const CHUNK_SIZE_Z := 1.0
+
+## Canonical chunk key: "{world_id}:{room_id}:{cx}:{cy}:{cz}".
+var key: String = ""
+## World id this chunk belongs to.
+var world_id: String = ""
+## Room id this chunk belongs to.
+var room_id: String = ""
+## Integer chunk coordinate along X.
+var cx: int = 0
+## Integer chunk coordinate along Y.
+var cy: int = 0
+## Integer chunk coordinate along Z.
+var cz: int = 0
+
+## Whether this chunk is currently loaded and active in the scene tree.
+var is_loaded := false
+
+## Emitted when the chunk has finished loading its content.
+signal chunk_loaded(chunk: Chunk)
+## Emitted when the chunk is about to be unloaded.
+signal chunk_unloaded(chunk: Chunk)
+
+
+## Build the canonical chunk key from the chunk's coordinates.
+func build_key() -> String:
+	return "%s:%s:%d:%d:%d" % [world_id, room_id, cx, cy, cz]
+
+
+## Compute the world-space origin (min corner) of this chunk.
+func world_origin() -> Vector2:
+	return Vector2(cx * CHUNK_SIZE_X, cy * CHUNK_SIZE_Y)
+
+
+## Compute the world-space bounding box of this chunk.
+func world_bounds() -> Rect2:
+	var origin := world_origin()
+	return Rect2(origin, Vector2(CHUNK_SIZE_X, CHUNK_SIZE_Y))
+
+
+## Compute the integer chunk coordinate for a world-space position.
+static func coord_for_position(pos: Vector2) -> Vector2i:
+	return Vector2i(
+		floori(pos.x / CHUNK_SIZE_X),
+		floori(pos.y / CHUNK_SIZE_Y)
+	)
+
+
+## Compute the canonical key for a world-space position.
+static func key_for_position(pos: Vector2, p_world_id: String, p_room_id: String) -> String:
+	var c := coord_for_position(pos)
+	return "%s:%s:%d:%d:0" % [p_world_id, p_room_id, c.x, c.y]
+
+
+## Load this chunk's content. In a real deployment this would fetch the chunk
+## payload from the server (see world.md §5.3 `request_chunk` / `chunk_data`)
+## and instantiate tiles/objects. For now it just marks the chunk loaded.
+func load_chunk() -> void:
+	is_loaded = true
+	chunk_loaded.emit(self)
+
+
+## Unload this chunk's content and free any child nodes.
+func unload_chunk() -> void:
+	chunk_unloaded.emit(self)
+	for child in get_children():
+		child.queue_free()
+	is_loaded = false