The Streaming Response That Committed Before the User Said Yes
The user is reading the agent's reasoning as it streams in. Around token 1200, the model decides to call send_email, then create_ticket, then kick_off_deploy. The user, watching the partial output and realizing the agent has misread the request, hits the stop button half a second too late. The email is already sent. The ticket is already filed. The deploy is already running. The stop button cancelled the next token, not the consequences of the last one.
The bug is not in the cancel handler. The bug is the assumption — borrowed from every other streaming UI on the team's roadmap — that an incrementally rendered output is an incrementally reversible one. Tool calls do not honor that contract. They are point-in-time commits that the streaming layer happily fires while the rest of the response is still being generated, and the cancel button has no way to chase them down the wire.
This is one of those failure modes that nobody owns because it lives in the seam between two teams that each shipped their half cleanly. The UX team shipped streaming because it tested better in user studies. The platform team shipped tool calls because the framework supports them. Neither team had a meeting where someone asked: what is "stop" supposed to mean when the response has already left the building?
