I was wondering how about privide an message type like Disconnect or something else before you send the PoisonPill  to the websocket Actor?
This would be nice one the webSocketActor could forward this message to the handler.then the handle know what hapend.
and seems like when you send the PosionPill to the websocketActor,then the handler may loose message that still in its mailbox.

Could you send the disconnect message to websocketActor and then forward to the handler,when the websocketActor received the disconnected message ,it forward the message to the handler actor and then following an PoisionPill message.when the handler actor received the disconnect message and I will know what happend ,and then I will stop by the PoisionPill message.
and the websocketActor will stop it finally cause it was wathing the handler.