One request, paused at the fork. It is held open until your handler resolves it, exactly once, and each resolver sends it somewhere different. Pick a branch and watch the same paused request take it.
GET /api/data continue_request() fail_request() fulfill_request() Browser the page that asked Server returns the real response blocked here page sees a net error 200 OK { your body, base64 } built locally, server never contacted Fetch.requestPaused PAUSED