feat: expose WebSocket serverOptions for crossws adapter

Problem

When using WebSocket with the graphql-ws protocol (for GraphQL subscriptions), browsers reject the connection with:

WebSocket connection failed: Error during WebSocket handshake: 
Sent non-empty 'Sec-WebSocket-Protocol' header but no response was received

This happens because crossws's node adapter has handleProtocols: () => false hardcoded:

// crossws/dist/adapters/node.mjs
const wss = options.wss || new _WebSocketServer({
  noServer: true,
  handleProtocols: () => false,  // ← Problem
  ...options.serverOptions       // ← Solution exists but not exposed
});

The ws library uses handleProtocols to negotiate WebSocket subprotocols. When it returns false, browsers reject the handshake even if we manually add Sec-WebSocket-Protocol header in the upgrade hook.

Current Workaround

Adding the header manually in the upgrade hook works for Node.js clients but not for browsers:

defineWebSocketHandler({
  upgrade(request) {
    const protocol = request.headers.get('sec-websocket-protocol')
    if (protocol?.includes('graphql-transport-ws')) {
      return {
        headers: { 'Sec-WebSocket-Protocol': 'graphql-transport-ws' }
      }
    }
  }
})

Proposed Solution

Expose serverOptions in Nitro's WebSocket configuration so users can customize the crossws adapter:

// nitro.config.ts
export default defineNitroConfig({
  features: {
    websocket: true
  },
  websocket: {
    serverOptions: {
      handleProtocols: (protocols) => {
        if (protocols.has('graphql-transport-ws')) {
          return 'graphql-transport-ws'
        }
        return false
      }
    }
  }
})

Or at minimum, allow passing serverOptions to the crossws adapter in the runtime presets.

Use Case

This is needed for GraphQL subscriptions over WebSocket using the graphql-ws protocol, which is the standard for:

• GraphQL Yoga
• Apollo Server
• Any GraphQL server implementing the graphql-ws spec

Environment

• Nitro: 3.0.1-alpha.1
• crossws: 0.4.1
• Node.js: 24.x

Related

• crossws adapter code: https://github.com/unjs/crossws/blob/main/src/adapters/node.ts
• graphql-ws protocol: https://github.com/enisdenjo/graphql-ws/blob/master/PROTOCOL.md

Start by tracing the websocket configuration from nitro.config.ts into the runtime presets and the crossws adapter at src/adapters/node.ts. Verify how serverOptions can reach the adapter, then check the GraphQL subprotocol handshake; done means users can configure handleProtocols without the manual upgrade-hook workaround.