fix(frontend): share one ThemeGuessGame instance across solo/matchmaking/rooms

ThemeGuessGame's constructor permanently binds click/mousemove/document
listeners onto the single shared #code-canvas/#category-panel. Solo,
matchmaking, and private-room flows each independently constructed their
own instance, so using more than one mode in the same page load (e.g.
Solo then Find Match) left multiple instances double-bound to the same
DOM, corrupting whichever mode was used first.

Add game/sharedGame.ts: a single lazily-constructed instance, reused via
setTheme/setSnippet and now-mutable onCategoryAssigned across every
flow. main.ts, matchmakingFlow.ts, and privateRoomFlow.ts now call
getSharedGame() instead of `new ThemeGuessGame(...)`.

Verified via CDP DOMDebugger.getEventListeners against a live session:
exactly one click/mousemove listener on #code-canvas after playing a
Solo round followed by a real matched Matchmaking round in the same
page load (previously would have been two of each).

frontend/src/game/ThemeGuessGame.ts

@@ -59,18 +59,26 @@ export class ThemeGuessGame {
   private height = 0;
   private categories!: CategoryStateMap;
 
-  /** `onCategoryAssigned`, when provided, fires at the end of every
-   * `applyColor` with the category and hex just assigned — multiplayer
-   * uses it to relay a bare `round:progress` and to track the local
-   * player's running color map for `round:submit`, without this class
-   * needing to know anything about the network. */
+  /** Fires at the end of every `applyColor` with the category and hex
+   * just assigned — multiplayer uses it to relay a bare
+   * `round:progress` and to track the local player's running color map
+   * for `round:submit`, without this class needing to know anything
+   * about the network. Mutable (not just constructor-set) because the
+   * app keeps a single shared `ThemeGuessGame` instance across
+   * solo/matchmaking/private-room (see `game/sharedGame.ts`) — whichever
+   * flow is currently active swaps this in rather than a new instance
+   * being constructed (which would double-bind canvas/document
+   * listeners onto the same DOM). */
+  onCategoryAssigned?: (id: CategoryId, hex: string) => void;
+
   constructor(
     themeId: ThemeId,
     snippetIndex: number = pickRandomSnippetIndex(),
-    private readonly onCategoryAssigned?: (id: CategoryId, hex: string) => void,
+    onCategoryAssigned?: (id: CategoryId, hex: string) => void,
   ) {
     this.themeId = themeId;
     this.snippetIndex = snippetIndex;
+    this.onCategoryAssigned = onCategoryAssigned;
     this.build();
     this.bindEvents();
     requestAnimationFrame((t) => this.loop(t));

frontend/src/game/sharedGame.ts

@@ -0,0 +1,40 @@
+// A single `ThemeGuessGame` bound to the page's one `#code-canvas` /
+// `#category-panel` / `#reveal-btn` / document-level listeners for its
+// entire lifetime. `ThemeGuessGame`'s constructor permanently binds
+// fresh event listeners onto those shared, singleton DOM elements and
+// never tears them down — constructing a *second* instance while a
+// first is still alive would double-bind every click/keydown/mousemove
+// handler onto the same elements, corrupting whichever mode the player
+// used first (e.g. two live color pickers fighting over the same
+// popover).
+//
+// Solo (`ui/soloConfigFlow.ts`), matchmaking (`ui/matchmakingFlow.ts`),
+// and private rooms (`ui/privateRoomFlow.ts`) each start their own
+// rounds/matches against the *same* canvas, so they must all share one
+// instance rather than each constructing their own — this module is
+// that shared instance's sole owner. Call `getSharedGame` every time a
+// flow is about to start a round: on the very first call it constructs
+// the instance; on every later call it reconfigures the existing one
+// (`setTheme`/`setSnippet`) and swaps in the caller's own
+// `onCategoryAssigned`, so exactly one set of DOM listeners ever exists,
+// always dispatching to whichever flow is currently active.
+
+import { ThemeGuessGame } from './ThemeGuessGame';
+import type { CategoryId, ThemeId } from '../types';
+
+let instance: ThemeGuessGame | null = null;
+
+export function getSharedGame(
+  themeId: ThemeId,
+  snippetIndex: number,
+  onCategoryAssigned?: (id: CategoryId, hex: string) => void,
+): ThemeGuessGame {
+  if (!instance) {
+    instance = new ThemeGuessGame(themeId, snippetIndex, onCategoryAssigned);
+    return instance;
+  }
+  instance.setTheme(themeId);
+  instance.setSnippet(snippetIndex);
+  instance.onCategoryAssigned = onCategoryAssigned;
+  return instance;
+}

frontend/src/main.ts

@@ -1,5 +1,5 @@
 import './style.css';
-import { ThemeGuessGame } from './game/ThemeGuessGame';
+import { getSharedGame } from './game/sharedGame';
 import { THEMES } from './data/themes';
 import { sound } from './engine/sound';
 import { createThemeGrid } from './ui/themeGrid';
@@ -56,8 +56,6 @@ function showView(name: ScreenName | null): void {
   }
 }
 
-let game: ThemeGuessGame | null = null;
-
 const themeGrid = createThemeGrid(themeGridEl, 'gruvbox', () => sound.playOpen());
 
 const soloConfigFlow = createSoloConfigFlow(
@@ -72,16 +70,7 @@ const soloConfigFlow = createSoloConfigFlow(
   (config) => {
     showView(null);
     runThemePreview(previewElements, config.themeId, () => {
-      if (game) {
-        game.setTheme(config.themeId);
-        game.setSnippet(config.snippetIndex);
-      } else {
-        game = new ThemeGuessGame(
-          config.themeId,
-          config.snippetIndex,
-          (id, hex) => soloConfigFlow.handleLocalAssignment(id, hex),
-        );
-      }
+      getSharedGame(config.themeId, config.snippetIndex, (id, hex) => soloConfigFlow.handleLocalAssignment(id, hex));
       themeNameBadge.textContent = THEMES[config.themeId].name;
       sound.playApply();
       soloConfigFlow.startTimer(config.timeMode);

frontend/src/ui/matchmakingFlow.ts

@@ -8,18 +8,15 @@
 // sends them in the opposite order — see the `foundAt`/`roundStartPayload`
 // handling below, which treats both orderings identically.
 //
-// Owns a single `OpponentView` / `ThemeGuessGame` / `MultiplayerMatch`
-// trio for the lifetime of the page, constructed lazily on the first
-// matchmaking round and reused (`setTheme`/`setSnippet`) on every
-// subsequent one — mirroring how `ui/soloConfigFlow.ts` reuses a single
-// `ThemeGuessGame` across solo replays. `ThemeGuessGame`'s constructor
-// binds fresh DOM listeners every time it's called, so constructing a
-// second one while a first is still alive (e.g. mixing solo/bot play
-// with matchmaking in the same page load) would double up event
-// handling; out of scope here, same single-orchestrator assumption
-// `game/multiplayerMatch.ts`'s header documents.
+// Owns a single `OpponentView` / `MultiplayerMatch` pair for the
+// lifetime of the page, constructed lazily on the first matchmaking
+// round and reused on every subsequent one. The `ThemeGuessGame` itself
+// is *not* owned here — it's the one shared instance from
+// `game/sharedGame.ts` (solo, matchmaking, and private rooms all start
+// rounds against the same `#code-canvas`, so exactly one instance must
+// ever exist; see that module's header for why).
 
-import { ThemeGuessGame } from '../game/ThemeGuessGame';
+import { getSharedGame } from '../game/sharedGame';
 import { MultiplayerMatch } from '../game/multiplayerMatch';
 import { OpponentView } from '../game/opponentView';
 import { THEMES } from '../data/themes';
@@ -103,7 +100,6 @@ export function createMatchmakingFlow(
   // every subsequent one this page load — see this module's header.
   let opponentView: OpponentView | null = null;
   let match: MultiplayerMatch | null = null;
-  let game: ThemeGuessGame | null = null;
 
   function clearBanTimers(): void {
     stopBanBanner?.();
@@ -194,14 +190,10 @@ export function createMatchmakingFlow(
     themeNameBadge.textContent = THEMES[payload.themeId].name;
 
     if (!opponentView) opponentView = new OpponentView('opponent-canvas', payload.snippetIndex);
+    const isNewMatch = !match;
     if (!match) match = new MultiplayerMatch(client, opponentView, handleLocalQuit);
-    if (!game) {
-      game = new ThemeGuessGame(payload.themeId, payload.snippetIndex, (id, hex) => match!.handleLocalAssignment(id, hex));
-      match.bindGame(game);
-    } else {
-      game.setTheme(payload.themeId);
-      game.setSnippet(payload.snippetIndex);
-    }
+    const game = getSharedGame(payload.themeId, payload.snippetIndex, (id, hex) => match!.handleLocalAssignment(id, hex));
+    if (isNewMatch) match.bindGame(game);
 
     hooks.showBoard();
     match.startRound(payload);

frontend/src/ui/privateRoomFlow.ts

@@ -16,33 +16,17 @@
 // its own listeners on the same client, so this flow must never react
 // to a round that belongs to a matchmaking match.
 //
-// Session component lifetime: exactly one `ThemeGuessGame` + one
-// `OpponentView` + one `MultiplayerMatch` are constructed, lazily, the
-// first time a room's first `round:start` arrives, then reused for
-// every subsequent match in that room's up-to-5-match series by calling
-// `match.startRound()` again — `MultiplayerMatch.startRound()` already
-// tears down and re-subscribes its own per-round listeners/timer, so
-// it's safe to call repeatedly on the same instance (confirmed by
-// reading its source; no fix needed there for this). Constructing a
-// *second* `ThemeGuessGame` for a later room, or for matchmaking, would
-// double-bind its canvas/document event listeners onto the single
-// shared `#code-canvas` — so this module's `game`/`opponentView`/`match`
-// are deliberately never rebuilt once created, only reconfigured via
-// `startRound`.
-//
-// Known cross-flow gap (see this ticket's final report): main.ts's own
-// solo-mode `game` singleton is *separately* constructed by
-// `soloConfigFlow`, hardcoding its `onCategoryAssigned` callback to
-// `soloConfigFlow.handleLocalAssignment` forever. If a player plays Solo
-// and then enters a private room in the same page load, this module
-// necessarily constructs its *own* `ThemeGuessGame`, which double-binds
-// listeners on the same `#code-canvas`/`#category-panel`/`document`
-// solo's instance already bound. Fixing this needs a shared, swappable
-// dispatch for `game`'s callback at the main.ts composition-root level
-// (mirroring how `soloConfigFlow` already multiplexes "alone" vs "vs
-// bot" internally) — out of this ticket's edit scope (main.ts's
-// `game`/`soloConfigFlow` construction block is off-limits here, see
-// this ticket's report).
+// Session component lifetime: one `OpponentView` + one `MultiplayerMatch`
+// are constructed, lazily, the first time a room's first `round:start`
+// arrives, then reused for every subsequent match in that room's
+// up-to-5-match series by calling `match.startRound()` again —
+// `MultiplayerMatch.startRound()` already tears down and re-subscribes
+// its own per-round listeners/timer, so it's safe to call repeatedly on
+// the same instance. The `ThemeGuessGame` itself is *not* owned here —
+// it's the one shared instance from `game/sharedGame.ts` (solo,
+// matchmaking, and this flow all start rounds against the same
+// `#code-canvas`, so exactly one instance must ever exist across the
+// whole page; see that module's header for why).
 
 import { THEMES } from '../data/themes';
 import type { GameClient } from '../net/client';
@@ -56,7 +40,7 @@ import type {
 } from '../net/messages';
 import { MultiplayerMatch } from '../game/multiplayerMatch';
 import { OpponentView } from '../game/opponentView';
-import { ThemeGuessGame } from '../game/ThemeGuessGame';
+import { getSharedGame } from '../game/sharedGame';
 import { openThemeVote, type ThemeVoteHandle } from './themeVote';
 
 export interface PrivateRoomFlowElements {
@@ -133,7 +117,6 @@ export function createPrivateRoomFlow(
   let transitionTimeoutId: number | null = null;
 
   let opponentView: OpponentView | null = null;
-  let game: ThemeGuessGame | null = null;
   let match: MultiplayerMatch | null = null;
   const splitView = requireEl<HTMLElement>('split-view');
 
@@ -335,9 +318,9 @@ export function createPrivateRoomFlow(
    * `multiplayerMatch.ts`'s documented two-phase-init order, then reuses
    * them for every later `round:start` this room sends. */
   function ensureMatch(payload: RoundStartMessage): MultiplayerMatch {
-    if (match && game) return match;
-
-    opponentView = new OpponentView('opponent-canvas', payload.snippetIndex);
+    if (!opponentView) opponentView = new OpponentView('opponent-canvas', payload.snippetIndex);
+    const isNewMatch = !match;
+    if (!match) {
       match = new MultiplayerMatch(client, opponentView, () => {
         // Local player quit mid-round: per PROTOCOL.md "Quit", the
         // quitter gets no room:closed of their own (only the remaining
@@ -347,8 +330,9 @@ export function createPrivateRoomFlow(
         callbacks.showMenu();
         render({ kind: 'hidden' });
       });
-    game = new ThemeGuessGame(payload.themeId, payload.snippetIndex, (id, hex) => match!.handleLocalAssignment(id, hex));
-    match.bindGame(game);
+    }
+    const game = getSharedGame(payload.themeId, payload.snippetIndex, (id, hex) => match!.handleLocalAssignment(id, hex));
+    if (isNewMatch) match.bindGame(game);
     return match;
   }