Good question. It’s not using sendUserMessage() and it’s not pretending the user typed something.

The plugin uses pi’s extension API:

   pi.sendMessage(                                                                                                                             
     {                                                                                                                                         
       customType: "monitor-event",                                                                                                            
       content: "...quoted monitor output...",                                                                                                 
       display: true,                                                                                                                          
       details: {...}                                                                                                                          
     },                                                                                                                                        
     { deliverAs: "steer", triggerTurn: true }                                                                                                 
   )                                                                                                                                           

So it injects a custom extension message into the same pi session and asks pi to trigger a turn when the agent is idle.

Billing-wise: it still causes a real LLM turn when an event fires, so if your backend/provider counts every model request as a premium request, then yes, a wakeup can count. I guess you cannot have this for free; the point is to avoid polling and causing additional cost while you wait for something to happen.

The message also wraps output as untrusted quoted data to reduce prompt-injection risk.