Start game via WebSocket intent (#3794)

## Description:

Replaces the HTTP POST /api/start_game/:id endpoint with a WebSocket
intent, making private game start consistent with how kick_player and
update_game_config already work. Also verifies that only the lobby
creator can start a game.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

src/client/HostLobbyModal.ts

@@ -1011,21 +1011,12 @@ export class HostLobbyModal extends BaseModal {
     // If the modal closes as part of starting the game, do not leave the lobby
     this.leaveLobbyOnClose = false;
 
-    const config = await getRuntimeClientServerConfig();
-    const response = await fetch(
-      `${window.location.origin}/${config.workerPath(this.lobbyId)}/api/start_game/${this.lobbyId}`,
-      {
-        method: "POST",
-        headers: {
-          "Content-Type": "application/json",
-        },
-      },
+    this.dispatchEvent(
+      new CustomEvent("start-game", {
+        bubbles: true,
+        composed: true,
+      }),
     );
-
-    if (!response.ok) {
-      this.leaveLobbyOnClose = true;
-    }
-    return response;
   }
 
   private kickPlayer(clientID: string) {

src/client/Main.ts

@@ -51,6 +51,7 @@ import { TerritoryPatternsModal } from "./TerritoryPatternsModal";
 import { TokenLoginModal } from "./TokenLoginModal";
 import {
   SendKickPlayerIntentEvent,
+  SendStartGameEvent,
   SendUpdateGameConfigIntentEvent,
 } from "./Transport";
 import { UserSettingModal } from "./UserSettingModal";
@@ -215,6 +216,7 @@ declare global {
   interface DocumentEventMap {
     "join-lobby": CustomEvent<JoinLobbyEvent>;
     "kick-player": CustomEvent;
+    "start-game": CustomEvent;
     "join-changed": CustomEvent;
     "open-matchmaking": CustomEvent<undefined>;
   }
@@ -311,6 +313,7 @@ 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("start-game", this.handleStartGame.bind(this));
     document.addEventListener(
       "update-game-config",
       this.handleUpdateGameConfig.bind(this),
@@ -932,6 +935,12 @@ class Client {
     }
   }
 
+  private handleStartGame() {
+    if (this.eventBus) {
+      this.eventBus.emit(new SendStartGameEvent());
+    }
+  }
+
   private handleUpdateGameConfig(event: CustomEvent) {
     const { config } = event.detail;
 

src/client/Transport.ts

@@ -173,6 +173,8 @@ export class SendUpdateGameConfigIntentEvent implements GameEvent {
   constructor(public readonly config: Partial<GameConfig>) {}
 }
 
+export class SendStartGameEvent implements GameEvent {}
+
 export class Transport {
   private socket: WebSocket | null = null;
 
@@ -262,6 +264,8 @@ export class Transport {
     this.eventBus.on(SendUpdateGameConfigIntentEvent, (e) =>
       this.onSendUpdateGameConfigIntent(e),
     );
+
+    this.eventBus.on(SendStartGameEvent, () => this.onSendStartGame());
   }
 
   private startPing() {
@@ -644,6 +648,10 @@ export class Transport {
     });
   }
 
+  private onSendStartGame() {
+    this.sendIntent({ type: "start_game" });
+  }
+
   private sendIntent(intent: Intent) {
     if (this.isLocal || this.socket?.readyState === WebSocket.OPEN) {
       const msg = {