feat(client): upgrade protocol decoder and GameState for v2 snapshot

Server shipped ObserverSnapshot v2 with game_time, player_facing,
visible_tiles (with visibility sectors), and per-entity visibility.
Protocol decoder was silently ignoring these fields. Now extracts
all v2 data with null defaults for backward compatibility.

GameState gains game_time, player_facing, visibility_sectors vars.
Derives visible_positions from visible_tiles when present (for real
server mode). Test snapshot updated with v2 fields.

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

client/scripts/protocol/protocol.gd

@@ -13,7 +13,9 @@ class_name Protocol
 # -- Decode: bytes from server → GDScript types --------------------------------
 
 ## Decode an ObserverSnapshot from MessagePack bytes.
-## Returns { "tick": int, "entities": Array[Dictionary] } or null on error.
+## Returns decoded snapshot Dictionary or null on error.
+## 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)
 	if result.status != null:
@@ -41,10 +43,41 @@ static func decode_snapshot(bytes: PackedByteArray) -> Variant:
 	# GDScript int is signed 64-bit. Rust tick is u64 but will not exceed 2^63
 	# in any realistic scenario (would require ~29 billion years at 10 ticks/game-minute per D-031).
 	var tick: int = raw["tick"]
+
+	# v2 fields — optional for backward compatibility
+	var version: Variant = raw.get("version")
+	var game_time: Variant = raw.get("game_time")
+
+	# player_facing: FacingDirection is a unit enum → bare string in rmp_serde
+	var player_facing: Variant = null
+	var raw_facing: Variant = raw.get("player_facing")
+	if raw_facing is String:
+		player_facing = raw_facing
+
+	# visible_tiles: Array of {x, y, z, visibility}
+	var visible_tiles: Array = []
+	var raw_vtiles: Variant = raw.get("visible_tiles")
+	if raw_vtiles is Array:
+		for raw_tile in raw_vtiles:
+			if raw_tile is Dictionary and raw_tile.has("x") and raw_tile.has("y") and raw_tile.has("z"):
+				var tile_entry := {
+					"x": int(raw_tile["x"]),
+					"y": int(raw_tile["y"]),
+					"z": int(raw_tile["z"]),
+				}
+				var vis: Variant = raw_tile.get("visibility")
+				if vis is String:
+					tile_entry["visibility"] = vis
+				visible_tiles.append(tile_entry)
+
 	return {
 		"tick": tick,
 		"entities": entities,
 		"decode_errors": dropped,
+		"version": version,
+		"game_time": game_time,
+		"player_facing": player_facing,
+		"visible_tiles": visible_tiles,
 	}
 
 
@@ -56,12 +89,20 @@ static func _decode_entity(raw: Dictionary) -> Variant:
 		return null
 
 	var entity_id: int = raw["entity_id"]
+
+	# v2: visibility sector (Forward/Peripheral). null for v1 entities.
+	var visibility: Variant = null
+	var raw_vis: Variant = raw.get("visibility")
+	if raw_vis is String:
+		visibility = raw_vis
+
 	return {
 		"entity_id": entity_id,
 		"x": float(raw["x"]),
 		"y": float(raw["y"]),
 		"z": int(raw["z"]),
 		"kind": _decode_enum_variant(raw["kind"]),
+		"visibility": visibility,
 	}