ws: server connection callback does not fire after successful upgrade #10898

Summary

After fixing #10888 so a custom-connection HTTP upgrade preserves Connection: Upgrade and hands the live socket to the client, the public ws@8.21.1 fixture advances through HTTP 101 and emits the client open event, but the WebSocketServer never emits connection. The end-to-end message exchange therefore remains blocked.

This is a distinct post-upgrade defect; the original Unexpected server response: 426 symptom is fixed.

Reproduction shape

1. Install ws@8.21.1 and compile the public ws entry from source.
2. Start new WebSocketServer({ port }).
3. Register a connection listener that registers a message listener.
4. Connect with new WebSocket(...) and send from its open listener.
5. Run with the fix(runtime): preserve dynamic parent for spread super #10886 and ws: public client/server fixture receives unexpected HTTP 426 response #10888 fixes applied.

Actual

A verbose run reports:

server listening
client initial nodebuffer 1006 false 0 0 0
client upgrade 101 websocket
client open
done

There is no server connection event. The end-to-end fixture reports:

serverGot=null
clientGot=null
RESULT: FAIL

Expected

The server emits connection, receives the client message, and the client receives the echo.

Provenance

Split from #10888 after its HTTP-layer 426 blocker was fixed. A direct node:http upgrade fixture now passes and verifies that the same detached socket receives bytes after the 101 response; this remaining failure is in the subsequent ws server connection/event path.