Out-of-tree port of JSS src/nostr/relay.js.

plugins: [{ module: 'relay/plugin.js', prefix: '/relay',
            config: { maxEvents: 1000, rateLimit: 60, persist: true } }]

WebSocket relay at the mount prefix. EVENT/REQ/CLOSE per NIP-01, replaceable + parameterized-replaceable + ephemeral kinds, per-socket rate limiting — feature parity with core, plus one improvement core doesn't have: events persist to api.storage.pluginDir() (JSONL), so the relay survives restarts.

• api.ws.route was sufficient for the whole realtime surface — no @fastify/websocket dependency, no upgrade handling, ~10 lines less glue than core's registration.
• Wall: event verification is internal. Core's src/nostr/event.js (validate/verify/sign, the #135 nostr-tools replacement) is not a documented import, so this port vendors a trimmed copy (nip01.js). Fine for a relay (crypto is a legitimate own dependency via @noble/curves), but any plugin wanting to verify nostr events the way the host does re-implements today. Candidate seam: export it like auth.js, e.g. javascript-solid-server/nostr.js.
• api.storage.pluginDir() immediately earned its keep — persistence was a 15-line add that core never grew.