fix broadcast id mismatch for matchmaking channel

main-server/app/channels/matchmaking_channel.rb

@@ -8,7 +8,10 @@
 #   5. Disconnecting (or sending { action: "stop" }) cancels the search.
 class MatchmakingChannel < ApplicationCable::Channel
   def subscribed
-    stream_for current_user
+    # NB: must mirror MatchmakingService.broadcast, which uses
+    # broadcast_to(user_id) → "matchmaking:<id>". stream_for(current_user)
+    # would use the GlobalID-based name and never receive those broadcasts.
+    stream_from "matchmaking:#{current_user.id}"
 
     # If a match was found while this user had no subscription
     # (e.g. brief reconnect), deliver it now — exactly once.