diff --git a/scripts/chunk.gd b/scripts/chunk.gd
index 1cbc21d..bb9d8cf 100644
--- a/scripts/chunk.gd
+++ b/scripts/chunk.gd
@@ -1,82 +1,105 @@
 class_name Chunk
-extends Node2D
-## A single loaded chunk in the world.
+extends Node3D
+## A single world chunk. Holds the chunk coordinate, bounds, and the
+## visual/gameplay content for that region of 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.
+## Chunks are the atomic unit of world geometry, gameplay objects, and
+## persistence (see docs/architecture/world.md). The server loads and saves
+## whole chunks; clients stream the chunks around them.
 
-## 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
+## Default chunk dimensions in world units (tiles). Matches the constants in
+## docs/architecture/world.md section 2.2.
+const CHUNK_SIZE_X: int = 32
+const CHUNK_SIZE_Y: int = 32
+const CHUNK_SIZE_Z: int = 1
 
-## Canonical chunk key: "{world_id}:{room_id}:{cx}:{cy}:{cz}".
+## World-space origin of chunk coordinate (0,0).
+const CHUNK_ORIGIN := Vector3(0.0, 0.0, 0.0)
+
+## Chunk coordinate (cx, cy, cz) in chunk space.
+var coord := Vector3i.ZERO
+
+## The canonical chunk key: "{world_id}:{room_id}:{cx}:{cy}:{cz}".
 var key: String = ""
-## World id this chunk belongs to.
+
+## World and room identifiers 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
+## Format version of the chunk payload (currently 1).
+var format_version: int = 1
 
-## 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)
+## Revision counter, incremented on every write. Used for optimistic
+## concurrency and change detection.
+var revision: int = 0
+
+## Whether this chunk has been modified in memory but not yet flushed.
+var dirty: bool = false
+
+## Container for static objects (props, geometry) in this chunk.
+var objects: Array[Node3D] = []
+
+## Container for dynamic object templates (spawnable entities).
+var dynamic_templates: Array[Node3D] = []
+
+## The world-space bounding box of this chunk.
+var bounds: AABB
 
 
-## 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]
+func _init(p_coord: Vector3i = Vector3i.ZERO, p_world_id: String = "", p_room_id: String = "") -> void:
+	coord = p_coord
+	world_id = p_world_id
+	room_id = p_room_id
+	key = build_key(world_id, room_id, coord)
+	bounds = compute_bounds(coord)
 
 
-## Compute the world-space origin (min corner) of this chunk.
-func world_origin() -> Vector2:
-	return Vector2(cx * CHUNK_SIZE_X, cy * CHUNK_SIZE_Y)
+## Build the canonical chunk key from its components.
+static func build_key(p_world_id: String, p_room_id: String, p_coord: Vector3i) -> String:
+	return "%s:%s:%d:%d:%d" % [p_world_id, p_room_id, p_coord.x, p_coord.y, p_coord.z]
 
 
-## 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 world-space bounding box for a chunk coordinate.
+static func compute_bounds(p_coord: Vector3i) -> AABB:
+	var min_pos := Vector3(
+		CHUNK_ORIGIN.x + p_coord.x * CHUNK_SIZE_X,
+		CHUNK_ORIGIN.y + p_coord.y * CHUNK_SIZE_Y,
+		CHUNK_ORIGIN.z + p_coord.z * CHUNK_SIZE_Z
+	)
+	return AABB(min_pos, Vector3(CHUNK_SIZE_X, CHUNK_SIZE_Y, CHUNK_SIZE_Z))
 
 
-## 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 chunk coordinate that contains a world-space position.
+static func coord_for_position(p_pos: Vector3) -> Vector3i:
+	return Vector3i(
+		int(floor((p_pos.x - CHUNK_ORIGIN.x) / CHUNK_SIZE_X)),
+		int(floor((p_pos.y - CHUNK_ORIGIN.y) / CHUNK_SIZE_Y)),
+		int(floor((p_pos.z - CHUNK_ORIGIN.z) / CHUNK_SIZE_Z))
 	)
 
 
-## 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]
+## Add a static object to this chunk.
+func add_object(p_object: Node3D) -> void:
+	objects.append(p_object)
+	add_child(p_object)
 
 
-## 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)
+## Add a dynamic object template to this chunk.
+func add_dynamic_template(p_template: Node3D) -> void:
+	dynamic_templates.append(p_template)
+	add_child(p_template)
 
 
-## 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
+## Remove all objects from this chunk.
+func clear_objects() -> void:
+	for obj in objects:
+		if is_instance_valid(obj):
+			obj.queue_free()
+	objects.clear()
+	dynamic_templates.clear()
+
+
+## Mark this chunk as dirty (modified but not yet persisted).
+func mark_dirty() -> void:
+	dirty = true
+	revision += 1