RivetKit Core WebSocket

Async close handlers

• Rivet actor WebSockets intentionally support async close handlers even though browser WebSocket close listeners are fire-and-forget.
• TypeScript actor code may return a Promise from ws.addEventListener("close", async handler) or ws.onclose = async handler.
• While a close handler promise is in flight, sleep readiness must report active WebSocket callback work and the actor must not finish sleeping.
• Core wraps close-event delivery in WebSocketCallbackRegion; the TypeScript native adapter opens one additional region per promise-returning user handler and closes that exact region when the promise settles.
• This is separate from onDisconnect gating. Close handlers are WebSocket event work; onDisconnect is connection lifecycle work.

Testing

• Core coverage lives in rivetkit-core websocket and sleep tests.
• Driver coverage lives in rivetkit-typescript/packages/rivetkit/tests/driver/actor-sleep.test.ts and actor-sleep-db.test.ts.