Real AI masters: rivals, AI seats and the co-op partner play by the player's rules (imps dig, mine and claim, rooms, towers, tunnels and the attack flag); other masters are saved; portals belong to whoever claims them

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/MULTIPLAYER.md

@@ -67,8 +67,10 @@ per turn. Fog of war, particles and the camera are local and not part of the sha
 - **Menu**: *Multiplayer* in the title menu with the match list, create (versus or co-op mission), join by code,
   seat choice, AI seat toggles for the host, ready/start, chat; the match keeps running in the background while
   menus are open.
-- **AI seats** (`Game::sync_ai_sides`): empty seats marked by the host and seats of players who left are played
-  by the simplified rival AI on every client, so they stay deterministic.
+- **AI seats** (`Game::sync_ai_sides`): empty seats marked by the host and seats of players who left keep their
+  master (dungeon, gold, creatures) and are played by the AI brain (`src/ai.rs`) on every client - the same
+  orders a player gives (dig, rooms, imps, towers, the attack flag, shields), from the shared state and the
+  shared random numbers, so they stay deterministic. Free-play and campaign rivals are such AI masters too.
 - **Co-op** (`Game::coop`): the master sides are allies against the heroes; allied creatures never target each
   other, allied ground does not block claims. Co-op campaign matches use `campaign::start_coop_mission`.
 - **Editor campaigns in co-op**: on the Match page the host can switch from the built-in campaign to the