A launch response can be lost in transit — a media-heavy study outlives Heroku's 30s router cap, the browser gets a 503, and the run it started is invisible to the only client that wanted it. The winning launch already publishes its response to Redis for LAUNCH_RESULT_TTL_S; this is how a client reads it back, so a dropped response becomes a reconnect rather than a duplicate study.

Scoped to the caller: the key is only ever looked up under the requesting user's own namespace.