fix(protocol): drop PROTOCOL_VERSION lockstep — D-192 (#875)

Removes the version-mismatch guard from Protocol.decode_snapshot() and the
PROTOCOL_VERSION constant from the client (server side done in #874).

Core changes:
- protocol.gd: remove const PROTOCOL_VERSION, remove version mismatch guard,
  remove "version" from return dict, add gauntlet_mode/room_id decode
- sim_bridge.gd: remove handshake version check; relax handshake guard to
  require only a valid Dictionary (server no longer sends protocol_version);
  emit handshake_complete(0) for API compat
- loading_screen.gd: drop "· protocol N" suffix from version label
- test_harness.gd: replace Protocol.PROTOCOL_VERSION with literal 23

Test updates (21 files): replace "version": Protocol.PROTOCOL_VERSION with
"version": 23 in all snapshot bytes dicts; remove snapshot.version == N
assertions; remove version-rejection tests (test_rejects_version_6,
test_decode_snapshot_rejects_missing_version, test_decode_snapshot_rejects_old_version,
test_protocol_rejects_version_mismatch, test_sim_bridge_test_snapshot_uses_current_protocol_version).

Also includes: #872 bookmark_catalog carry-forward regression test, and
#873 merge-path flow tests (test_merge_path_flows_sprint37.gd).

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

client/scripts/protocol/protocol.gd

@@ -9,13 +9,6 @@ extends Node
 ##   Unit enum variants (no data) → bare strings ("MoveNorth", "Npc")
 ##   Data enum variants → single-element maps ({"UsePerceptionMode": "thermal"})
 
-## Protocol version — must match server PROTOCOL_VERSION in bridge/types.rs.
-## Reject snapshots where version != this value.
-## v20: adds settings_response field to ObserverSnapshot (#627, D-138).
-## v21: adds economy_snapshot field to ObserverSnapshot (#822, D-181).
-## v23: adds bookmark_catalog field to ObserverSnapshot (#614).
-const PROTOCOL_VERSION: int = 23
-
 # -- Decode: bytes from server → GDScript types --------------------------------
 
 
@@ -34,17 +27,6 @@ static func decode_snapshot(bytes: PackedByteArray) -> Variant:
 		push_error("Protocol: snapshot missing required fields")
 		return null
 
-	# Version check: reject snapshots from incompatible server
-	var version: Variant = raw.get("version")
-	if version != PROTOCOL_VERSION:
-		push_error(
-			(
-				"Protocol: version mismatch (got %s, expected %s). Server and client are out of sync."
-				% [version, PROTOCOL_VERSION]
-			)
-		)
-		return null
-
 	var entities: Array[Dictionary] = []
 	var raw_entities: Array = raw["entities"]
 	var dropped := 0
@@ -67,7 +49,7 @@ static func decode_snapshot(bytes: PackedByteArray) -> Variant:
 	# in any realistic scenario (would require ~29 billion years at 10 ticks/game-minute per D-031).
 	var tick: int = raw["tick"]
 
-	# version already checked above; game_time for HUD display
+	# game_time for HUD display
 	var game_time: Variant = raw.get("game_time")
 
 	# player_facing: FacingDirection is a unit enum → bare string in rmp_serde
@@ -223,6 +205,18 @@ static func decode_snapshot(bytes: PackedByteArray) -> Variant:
 			"speaker_entity_id": int(raw_dr.get("speaker_entity_id", -1)),
 		}
 
+	# v8: gauntlet_mode and room_id (#496) — present only in Gauntlet sessions.
+	# gauntlet_mode is a bool flag; room_id is a String room identifier or absent.
+	# Snapshot handler (snapshot_handler.gd) reads these via snapshot.has() guards.
+	var gauntlet_mode: bool = false
+	var raw_gauntlet: Variant = raw.get("gauntlet_mode")
+	if raw_gauntlet == true:
+		gauntlet_mode = true
+	var room_id: Variant = null
+	var raw_room_id: Variant = raw.get("room_id")
+	if raw_room_id is String:
+		room_id = raw_room_id
+
 	# v9: conversation_events (#535, D-078) — overheard NPC-to-NPC dialogue lines.
 	# Each event carries pre-occluded text plus speaker/target attribution.
 	var conversation_events: Array = []
@@ -484,7 +478,6 @@ static func decode_snapshot(bytes: PackedByteArray) -> Variant:
 		"tick": tick,
 		"entities": entities,
 		"decode_errors": dropped,
-		"version": version,
 		"game_time": game_time,
 		"player_facing": player_facing,
 		"player_stance": player_stance,
@@ -508,6 +501,8 @@ static func decode_snapshot(bytes: PackedByteArray) -> Variant:
 		"current_ticker": current_ticker,
 		"settings_response": settings_response,
 		"bookmark_catalog": bookmark_catalog,
+		"gauntlet_mode": gauntlet_mode,
+		"room_id": room_id,
 	}
 
 

client/scripts/protocol/test_harness.gd

@@ -272,7 +272,7 @@ func snapshot() -> Dictionary:
 
 	return {
 		"tick": tick,
-		"version": Protocol.PROTOCOL_VERSION,
+		"version": 23,
 		"game_time":
 		{
 			"day": 0,