fix(client): parse-order fixes for Protocol autoload and MetaScreen extends

Protocol.gd is an autoload — replace Messagepack class_name refs with
inline load() calls via a static helper. main_menu.gd extends MetaScreen
by class_name which fails at parse time; switch to path-based extends.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/scripts/protocol/protocol.gd

@@ -9,6 +9,9 @@ extends Node
 ##   Unit enum variants (no data) → bare strings ("MoveNorth", "Npc")
 ##   Data enum variants → single-element maps ({"UsePerceptionMode": "thermal"})
 
+static func _mp():
+	return load("res://addons/messagepack/messagepack.gd")
+
 # -- Decode: bytes from server → GDScript types --------------------------------
 
 
@@ -17,7 +20,7 @@ extends Node
 ## v2 fields (version, game_time, player_facing, visible_tiles) default to null/empty
 ## when decoding v1 snapshots for backward compatibility.
 static func decode_snapshot(bytes: PackedByteArray) -> Variant:
-	var result = Messagepack.decode(bytes)
+	var result = _mp().decode(bytes)
 	if result.status != null:
 		push_error("Protocol: msgpack decode failed: %s" % result.status)
 		return null
@@ -625,7 +628,7 @@ static func encode_startup_message(
 	}
 	if character_visual != null and character_visual.has_method("to_dict"):
 		msg["character_visual_descriptor"] = character_visual.to_dict()
-	var result = Messagepack.encode(msg)
+	var result = _mp().encode(msg)
 	if result.status != null:
 		push_error("Protocol: startup message encode failed: %s" % result.status)
 		return PackedByteArray()
@@ -646,7 +649,7 @@ static func encode_player_input(
 		"action": action_value,
 	}
 
-	var result = Messagepack.encode(input)
+	var result = _mp().encode(input)
 	if result.status != null:
 		push_error("Protocol: msgpack encode failed: %s" % result.status)
 		return PackedByteArray()
@@ -672,7 +675,7 @@ static func encode_player_inputs(inputs: Array) -> PackedByteArray:
 			)
 		)
 
-	var result = Messagepack.encode(wire_inputs)
+	var result = _mp().encode(wire_inputs)
 	if result.status != null:
 		push_error("Protocol: msgpack encode failed: %s" % result.status)
 		return PackedByteArray()
@@ -705,7 +708,7 @@ static func encode_change_settings(enabled: bool) -> PackedByteArray:
 			"action_data": {"ai_enhanced_dialogue": enabled},
 		}
 	]
-	var result = Messagepack.encode(entries)
+	var result = _mp().encode(entries)
 	if result.status != null:
 		push_error("Protocol: encode_change_settings failed: %s" % result.status)
 		return PackedByteArray()
@@ -716,7 +719,7 @@ static func encode_change_settings(enabled: bool) -> PackedByteArray:
 ## Unit variant — no payload. Server responds with bookmark_catalog in the next snapshot.
 static func encode_request_bookmark_catalog() -> PackedByteArray:
 	var entries: Array = [{"tick": 0, "action_name": "RequestBookmarkCatalog", "action_data": null}]
-	var result = Messagepack.encode(entries)
+	var result = _mp().encode(entries)
 	if result.status != null:
 		push_error("Protocol: encode_request_bookmark_catalog failed: %s" % result.status)
 		return PackedByteArray()
@@ -733,7 +736,7 @@ static func encode_confirm_bookmark(bookmark_id: String, starting_location_id: S
 			"action_data": {"bookmark_id": bookmark_id, "starting_location_id": starting_location_id},
 		}
 	]
-	var result = Messagepack.encode(entries)
+	var result = _mp().encode(entries)
 	if result.status != null:
 		push_error("Protocol: encode_confirm_bookmark failed: %s" % result.status)
 		return PackedByteArray()
@@ -743,7 +746,7 @@ static func encode_confirm_bookmark(bookmark_id: String, starting_location_id: S
 ## Decode a PlayerInput from MessagePack bytes (used in tests / echo scenarios).
 ## Returns { "tick": int, "action": { "variant": String, "data": Variant } } or null.
 static func decode_player_input(bytes: PackedByteArray) -> Variant:
-	var result = Messagepack.decode(bytes)
+	var result = _mp().decode(bytes)
 	if result.status != null:
 		push_error("Protocol: msgpack decode failed: %s" % result.status)
 		return null

client/ui/meta/screens/main_menu/main_menu.gd

@@ -1,4 +1,4 @@
-extends MetaScreen
+extends "res://ui/meta/meta_screen.gd"
 ## #258: Main menu — New Game / Continue / Load Game / Quit.
 ## New Game: opens character creation screen, then starts game.
 ## Continue: loads most recent save directory.