Element Bound

Multiplayer client entry point

Multiplayer mode is additive and activates only when the player interacts with the Online Match panel or the page has a roomId query parameter, for example /?roomId=manual-test-room. The browser initializes the Firebase compat SDK and signs the player in anonymously before enabling Create/Join. Single-player startup remains unchanged.

The deployment must define the public Firebase Web configuration variables FIREBASE_WEB_API_KEY and FIREBASE_PROJECT_ID. Optional values are FIREBASE_AUTH_DOMAIN, FIREBASE_STORAGE_BUCKET, FIREBASE_MESSAGING_SENDER_ID, and FIREBASE_APP_ID. The /api/firebase-config endpoint exposes only these public client settings; Admin credentials remain server-only. Anonymous Authentication must also be enabled in Firebase Console under Authentication → Sign-in method.

Server endpoints also require FIREBASE_PROJECT_ID, FIREBASE_CLIENT_EMAIL, and a Firebase Admin private key. Prefer the single-line FIREBASE_PRIVATE_KEY_B64 setting in Vercel; generate it from a downloaded service-account JSON file with jq -jr '.private_key' service-account.json | base64 | tr -d '\n'. The legacy FIREBASE_PRIVATE_KEY setting remains supported for raw PEM values and values containing escaped \\n newlines.

Test hosts may instead define window.EB_MULTIPLAYER_DEPS before js/game.js loads with {user, db, fetchImpl?}. The user must expose uid and getIdToken(), while db must expose the Firestore compat collection().doc().onSnapshot() interface.

In multiplayer mode, moves are posted to /api/submit-move and the board is rendered only from rooms/{roomId}/views/{uid} snapshots. Without a roomId, the existing single-player startup and local game loop are unchanged.

Authenticated players can create a direct-invite room from the home screen after choosing a deck. The creator receives a ?join=ROOMID share link; the invited player chooses their own deck and joins, after which both clients transition to the existing ?roomId=ROOMID live-view flow. A playable authoritative state is created only when both deck selections are known.