fix: transfer host when lobby creator disconnects

When the host of a private lobby disconnects, transfer host role to the
next active player. The new host's JoinLobbyModal automatically converts
to a HostLobbyModal with full controls (edit settings, kick, start).
Nation count and other config values are preserved from the original host.

resources/lang/en.json

@@ -432,7 +432,8 @@
     "starting_gold": "Starting gold",
     "crowded": "Crowded modifier",
     "hard_nations": "Hard Nations",
-    "leave_confirmation": "Are you sure you want to leave the lobby?"
+    "leave_confirmation": "Are you sure you want to leave the lobby?",
+    "you_are_now_host": "You are now the host of this lobby."
   },
   "team_colors": {
     "red": "Red",

src/client/HostLobbyModal.ts

@@ -35,6 +35,7 @@ import {
   getNationsForCompactMap,
   getRandomMapType,
   getUpdatedDisabledUnits,
+  nationsConfigToSlider,
   parseBoundedFloatFromInput,
   parseBoundedIntegerFromInput,
   preventDisallowedKeys,
@@ -393,6 +394,71 @@ export class HostLobbyModal extends BaseModal {
     this.loadNationCount();
   }
 
+  /**
+   * Open the host modal for an existing lobby (e.g. after host transfer).
+   * Unlike normal open(), this does NOT create a new lobby or emit join-lobby.
+   */
+  public openExisting(
+    lobbyId: string,
+    gameConfig: GameConfig,
+    clients: ClientInfo[],
+  ): void {
+    super.open();
+    this.startLobbyUpdates();
+    this.lobbyId = lobbyId;
+
+    // Hydrate form state from the existing game config
+    this.selectedMap = gameConfig.gameMap;
+    this.selectedDifficulty = gameConfig.difficulty;
+    this.gameMode = gameConfig.gameMode;
+    this.teamCount = gameConfig.playerTeams ?? 2;
+    this.bots = gameConfig.bots;
+    this.infiniteGold = gameConfig.infiniteGold;
+    this.donateGold = gameConfig.donateGold;
+    this.infiniteTroops = gameConfig.infiniteTroops;
+    this.donateTroops = gameConfig.donateTroops;
+    this.instantBuild = gameConfig.instantBuild;
+    this.randomSpawn = gameConfig.randomSpawn;
+    this.compactMap = gameConfig.gameMapSize === GameMapSize.Compact;
+    this.disabledUnits = gameConfig.disabledUnits ?? [];
+    this.spawnImmunity =
+      gameConfig.spawnImmunityDuration !== undefined &&
+      gameConfig.spawnImmunityDuration > 0;
+    this.spawnImmunityDurationMinutes = this.spawnImmunity
+      ? Math.round((gameConfig.spawnImmunityDuration ?? 0) / (60 * 10))
+      : undefined;
+    this.maxTimer =
+      gameConfig.maxTimerValue !== undefined && gameConfig.maxTimerValue > 0;
+    this.maxTimerValue = gameConfig.maxTimerValue;
+    this.goldMultiplier =
+      gameConfig.goldMultiplier !== undefined && gameConfig.goldMultiplier > 0;
+    this.goldMultiplierValue = gameConfig.goldMultiplier;
+    this.startingGold =
+      gameConfig.startingGold !== undefined && gameConfig.startingGold > 0;
+    this.startingGoldValue =
+      gameConfig.startingGold !== undefined
+        ? gameConfig.startingGold / 1_000_000
+        : undefined;
+
+    this.clients = clients;
+
+    // Set up URL and invite button
+    void (async () => {
+      crazyGamesSDK.showInviteButton(this.lobbyId);
+      const url = await this.constructUrl();
+      this.updateHistory(url);
+    })();
+
+    if (this.modalEl) {
+      this.modalEl.onClose = () => {
+        this.close();
+      };
+    }
+    // Load default nation count from map, then restore the actual nation
+    // value from the existing config (instead of resetting to the default).
+    this.loadNationCountThenRestore(gameConfig.nations);
+  }
+
   private leaveLobby() {
     if (!this.lobbyId) {
       return;
@@ -857,6 +923,26 @@ export class HostLobbyModal extends BaseModal {
       // Leave existing values unchanged so the UI stays consistent
     }
   }
+
+  /**
+   * Load the default nation count from the map manifest, then restore
+   * the nation slider to the value from an existing GameConfig.
+   */
+  private async loadNationCountThenRestore(
+    nations: GameConfig["nations"],
+  ): Promise<void> {
+    const currentMap = this.selectedMap;
+    try {
+      const mapData = this.mapLoader.getMapData(currentMap);
+      const manifest = await mapData.manifest();
+      if (this.selectedMap === currentMap) {
+        this.defaultNationCount = manifest.nations.length;
+        this.nations = nationsConfigToSlider(nations, this.defaultNationCount);
+      }
+    } catch (error) {
+      console.warn("Failed to load nation count for restore", error);
+    }
+  }
 }
 
 async function createLobby(gameID: string): Promise<GameInfo> {

src/client/JoinLobbyModal.ts

@@ -50,6 +50,7 @@ export class JoinLobbyModal extends BaseModal {
   private leaveLobbyOnClose = true;
   private countdownTimerId: number | null = null;
   private handledJoinTimeout = false;
+  private hostTransferDispatched = false;
 
   private isPrivateLobby(): boolean {
     return this.gameConfig?.gameType === GameType.Private;
@@ -66,6 +67,27 @@ export class JoinLobbyModal extends BaseModal {
       ...lobby,
       startsAt: lobby.startsAt ?? undefined,
     });
+    // If this client has become the host of a private lobby, switch to HostLobbyModal
+    if (
+      !this.hostTransferDispatched &&
+      this.isPrivateLobby() &&
+      this.currentClientID &&
+      lobby.lobbyCreatorClientID &&
+      this.currentClientID === lobby.lobbyCreatorClientID
+    ) {
+      this.hostTransferDispatched = true;
+      this.dispatchEvent(
+        new CustomEvent("host-transfer", {
+          detail: {
+            lobbyId: this.currentLobbyId,
+            gameConfig: this.gameConfig,
+            clients: this.players,
+          },
+          bubbles: true,
+          composed: true,
+        }),
+      );
+    }
   };
 
   render() {
@@ -329,6 +351,7 @@ export class JoinLobbyModal extends BaseModal {
     this.lobbyCreatorClientID = null;
     this.isConnecting = true;
     this.handledJoinTimeout = false;
+    this.hostTransferDispatched = false;
     this.startLobbyUpdates();
     if (lobbyInfo) {
       this.updateFromLobby(lobbyInfo);
@@ -378,6 +401,7 @@ export class JoinLobbyModal extends BaseModal {
     this.lobbyCreatorClientID = null;
     this.isConnecting = true;
     this.leaveLobbyOnClose = true;
+    this.hostTransferDispatched = false;
   }
 
   disconnectedCallback() {

src/client/Main.ts

@@ -212,6 +212,7 @@ declare global {
   interface DocumentEventMap {
     "join-lobby": CustomEvent<JoinLobbyEvent>;
     "kick-player": CustomEvent;
+    "host-transfer": CustomEvent;
     "join-changed": CustomEvent;
     "open-matchmaking": CustomEvent<undefined>;
   }
@@ -313,6 +314,10 @@ class Client {
     document.addEventListener("join-lobby", this.handleJoinLobby.bind(this));
     document.addEventListener("leave-lobby", this.handleLeaveLobby.bind(this));
     document.addEventListener("kick-player", this.handleKickPlayer.bind(this));
+    document.addEventListener(
+      "host-transfer",
+      this.handleHostTransfer.bind(this),
+    );
     document.addEventListener(
       "update-game-config",
       this.handleUpdateGameConfig.bind(this),
@@ -895,6 +900,29 @@ class Client {
     }
   }
 
+  private handleHostTransfer(event: CustomEvent) {
+    const { lobbyId, gameConfig, clients } = event.detail;
+    if (!lobbyId || !gameConfig) {
+      console.warn("host-transfer event missing required data");
+      return;
+    }
+    // Close JoinLobbyModal without leaving the lobby (we're staying in the same game)
+    this.joinModal?.closeWithoutLeaving();
+    // Switch to the HostLobbyModal page and open with existing lobby state
+    window.showPage?.("page-host-lobby");
+    this.hostModal?.openExisting(lobbyId, gameConfig, clients ?? []);
+    // Notify the new host
+    window.dispatchEvent(
+      new CustomEvent("show-message", {
+        detail: {
+          message: translateText("host_modal.you_are_now_host"),
+          color: "green",
+          duration: 4000,
+        },
+      }),
+    );
+  }
+
   private handleUpdateGameConfig(event: CustomEvent) {
     const { config } = event.detail;
 

src/server/GameServer.ts

@@ -503,6 +503,7 @@ export class GameServer {
       this.activeClients = this.activeClients.filter(
         (c) => c.clientID !== client.clientID,
       );
+      this.maybeTransferHost(client);
     });
     client.ws.on("error", (error: Error) => {
       if ((error as any).code === "WS_ERR_UNEXPECTED_RSV_1") {
@@ -522,6 +523,30 @@ export class GameServer {
     }
   }
 
+  private maybeTransferHost(disconnectedClient: Client): void {
+    // Only transfer host in the lobby phase for private games
+    if (this._hasStarted || this._hasEnded || this.isPublic()) {
+      return;
+    }
+    // Only transfer if the disconnected client was the host
+    if (disconnectedClient.clientID !== this.lobbyCreatorID) {
+      return;
+    }
+    const newHost = this.activeClients[0];
+    if (!newHost) {
+      return;
+    }
+    this.creatorPersistentID = newHost.persistentID;
+    this.log.info("Transferred lobby host", {
+      oldHostClientID: disconnectedClient.clientID,
+      newHostClientID: newHost.clientID,
+      newHostPersistentID: newHost.persistentID,
+      gameID: this.id,
+    });
+    // Immediately broadcast updated lobby info so clients see the new host
+    this.broadcastLobbyInfo();
+  }
+
   public setStartsAt(startsAt: number) {
     this.startsAt = startsAt;
   }