@nexus/backend

The composable server side of the Nexus game engine: the Gateway (REST + WS), the Room/Session service (lifecycle, caveat sanity, pots), and the Indexer (World Store events → queryable tables → WS fan-out). Everything sits behind a port with a default adapter (backend spec §2). Phases 05 + 06.

Composition root

import { createBackend, createGatewayApp, rateLimit } from "@nexus/backend";
import { DirectRelayer } from "@nexus/relayer";
import uno from "./games/uno";

const backend = createBackend({
  chain: "base",
  world: process.env.WORLD_ADDRESS,
  relayer: new DirectRelayer({ ... }),   // OneShotRelayer in prod
  games: [uno],                          // auto-mounted at /game/uno
  // indexer, facilitator, sessionStore → defaults
});
backend.use(rateLimit({ perRoom: 50 }));
await backend.start();                    // resolves capabilities, starts indexer

const app = createGatewayApp(backend);    // Hono app — mount or `serve` it

Routes (backend spec §4.1 — exhaustive)

| Method | Path | Routes to | |---|---|---| | POST | /game/:name/join | RoomService.joinRoom (validates caveats) | | POST | /game/:name/move | move lifecycle → Relayer.submitBundle | | POST | /game/:name/charge | charge lifecycle → Facilitator + Relayer | | GET | /game/:name/state/:table | IndexerAdapter.query | | WS | /game/:name/subscribe | IndexerAdapter.subscribe (WsHub fan-out) | | POST | /nexus/webhook | WebhookHandler.ingest (1Shot status) | | GET | /healthz /readyz | ops |

Adapters (ports + defaults)

• RelayerAdapter (from @nexus/relayer) — required, injected.
• FacilitatorAdapter (from @nexus/server) — default StubFacilitator; Phase 07 swaps in DelegationFacilitator with zero gateway diff.
• IndexerAdapter — default InMemoryIndexer; NexusIndexer (Postgres + WS) is a documented seam (see indexer/nexus-indexer.ts).
• SessionStore — default MemorySessionStore; Redis store documented in rooms/store.ts.
• Middleware — backend.use(mw), run in registration order, sees every request and every redemption.

Documented seams

• NexusIndexer (Postgres + WS, reorg/finality/backfill/reconcile) — phase-06.
• RedisSessionStore + Redis webhook ledger — shapes documented inline.
• EIP-1271 smart-account auth — verifyRequest({ verify1271 }) hook for deployed contract wallets (EIP-191 personal_sign verified by default).