feat: auto-start listed lobbies after 5 minutes

Hosts can't sit on a public listing: setListed(true) records listedAt,
and once listedAt + HOSTED_LOBBY_AUTO_START_MS passes, GameManager's
tick arms the normal start countdown (same path as the host's Start
button, honoring startDelay). Cancelling the countdown re-arms on the
next tick; unlisting cancels the deadline and relisting starts a fresh
one. Duplicate setListed(true) calls don't extend it.

The deadline rides to the host as autoStartAt in lobby info, rendered
as an amber countdown next to the Public/Private switch in the host
modal header (hidden once the real start countdown takes over).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/client/HostLobbyModal.ts

@@ -1,4 +1,4 @@
-import { html } from "lit";
+import { html, nothing } from "lit";
 import { customElement, property, state } from "lit/decorators.js";
 import { ClientEnv } from "src/client/ClientEnv";
 import {
@@ -112,6 +112,8 @@ export class HostLobbyModal extends BaseModal {
   @state() private canListPublicly: boolean = false;
   @state() private publiclyListed: boolean = false;
   @state() private showSubscriptionRequired: boolean = false;
+  // Server timestamp when the listed lobby auto-starts (from lobby info).
+  @state() private autoStartAt: number | null = null;
 
   @property({ attribute: false }) eventBus: EventBus | null = null;
   // Timers for debouncing slider changes
@@ -146,6 +148,7 @@ export class HostLobbyModal extends BaseModal {
     if (!this.listingRequestInFlight && lobby.listed !== undefined) {
       this.publiclyListed = lobby.listed;
     }
+    this.autoStartAt = lobby.autoStartAt ?? null;
   };
 
   private getRandomString(): string {
@@ -248,9 +251,32 @@ export class HostLobbyModal extends BaseModal {
         ${segment("host_modal.visibility_private", false)}
         ${segment("host_modal.visibility_public", true)}
       </div>
+      ${this.renderAutoStartTimer()}
     `;
   }
 
+  // Countdown until the listed lobby starts automatically (hosts can't sit
+  // on a public listing). Hidden once the real start countdown is running —
+  // the Start button shows that one.
+  private renderAutoStartTimer() {
+    if (
+      !this.publiclyListed ||
+      this.autoStartAt === null ||
+      this.lobbyStartAt !== null
+    ) {
+      return nothing;
+    }
+    const seconds = getSecondsUntilServerTimestamp(
+      this.autoStartAt,
+      this.serverTimeOffset,
+    );
+    return html`<span
+      class="text-amber-300 text-xs font-bold tabular-nums shrink-0"
+      title=${translateText("host_modal.auto_start_timer")}
+      >${renderDuration(seconds)}</span
+    >`;
+  }
+
   private handleVisibilitySelect(isPublic: boolean) {
     if (
       this.listingRequestInFlight ||
@@ -738,6 +764,7 @@ export class HostLobbyModal extends BaseModal {
     this.hostCheatStartingGoldValue = undefined;
     this.publiclyListed = false;
     this.showSubscriptionRequired = false;
+    this.autoStartAt = null;
 
     this.leaveLobbyOnClose = true;
   }

src/core/Schemas.ts

@@ -176,6 +176,11 @@ export type ScheduledPublicGameType = z.infer<
 // and delists any overflow as the authoritative backstop.
 export const MAX_HOSTED_LOBBIES = 10;
 
+// How long a lobby may stay publicly listed before it starts automatically,
+// so hosts can't sit on a listing indefinitely. Unlisting cancels the
+// deadline; relisting starts a fresh one.
+export const HOSTED_LOBBY_AUTO_START_MS = 5 * 60 * 1000;
+
 export const UsernameSchema = z
   .string()
   .regex(/^(?=.*\S)[a-zA-Z0-9_ üÜ.]+$/u)
@@ -207,6 +212,9 @@ export const GameInfoSchema = z.object({
   // UI stays in sync when the server delists (whitelist enabled, duplicate
   // creator resolved by the master).
   listed: z.boolean().optional(),
+  // Listed lobbies only: server timestamp when the lobby starts
+  // automatically (hosts can't sit on a public listing indefinitely).
+  autoStartAt: z.number().optional(),
 });
 
 // Browser-facing lobby info. Master/worker-internal fields (the creator hash

src/server/GameManager.ts

@@ -126,6 +126,9 @@ export class GameManager {
     const active = new Map<GameID, GameServer>();
     for (const [id, game] of this.games) {
       const phase = game.phase();
+      if (phase === GamePhase.Lobby) {
+        game.maybeAutoStartListed();
+      }
       if (phase === GamePhase.Active) {
         if (!game.hasStarted()) {
           // Prestart tells clients to start loading the game.

src/server/GameServer.ts

@@ -15,6 +15,7 @@ import {
   GameInfo,
   GameStartInfo,
   GameStartInfoSchema,
+  HOSTED_LOBBY_AUTO_START_MS,
   Intent,
   LiveStats,
   PlayerLiveStats,
@@ -149,6 +150,9 @@ export class GameServer {
   // only the authenticated /api/game/:id/listing endpoint may (it verifies
   // the creator's subscription).
   private listed = false;
+  // When the lobby was listed; drives the auto-start deadline. Cleared on
+  // delist, so relisting starts a fresh deadline.
+  private listedAt?: number;
 
   private lobbyInfoIntervalId: ReturnType<typeof setInterval> | null = null;
 
@@ -274,7 +278,7 @@ export class GameServer {
       // A join whitelist and public listing are mutually exclusive: a listed
       // lobby must be joinable by anyone who finds it in the lobby browser.
       if (this.listed && this.hasJoinWhitelist()) {
-        this.listed = false;
+        this.setListed(false);
         this.log.info("delisted lobby: join whitelist enabled");
       }
     }
@@ -1154,6 +1158,7 @@ export class GameServer {
       serverTime: Date.now(),
       publicGameType: this.publicGameType,
       listed: this.isPublic() ? undefined : this.listed,
+      autoStartAt: this.autoStartAt(),
     };
   }
 
@@ -1183,7 +1188,38 @@ export class GameServer {
   }
 
   public setListed(listed: boolean): void {
+    if (this.listed === listed) {
+      // Duplicate toggles must not extend the auto-start deadline.
+      return;
+    }
     this.listed = listed;
+    this.listedAt = listed ? Date.now() : undefined;
+  }
+
+  // Deadline after which a listed lobby starts automatically, so hosts
+  // can't sit on a public listing indefinitely.
+  public autoStartAt(): number | undefined {
+    return this.listed && this.listedAt !== undefined
+      ? this.listedAt + HOSTED_LOBBY_AUTO_START_MS
+      : undefined;
+  }
+
+  // Called from GameManager's tick while in the Lobby phase: once the
+  // listed deadline passes, arm the normal start countdown (same path as
+  // the host's Start button). Cancelling the countdown re-arms it on the
+  // next tick, so the only way out is to unlist.
+  public maybeAutoStartListed(): void {
+    if (this.hasStarted() || this.startsAt !== undefined) {
+      return;
+    }
+    const deadline = this.autoStartAt();
+    if (deadline === undefined || Date.now() < deadline) {
+      return;
+    }
+    this.log.info("listed lobby reached auto-start deadline, starting", {
+      gameID: this.id,
+    });
+    this.setStartsAt(Date.now() + (this.gameConfig.startDelay ?? 0) * 1000);
   }
 
   // Whether joining is restricted to an allowlist of publicIds. A lobby with