Discriminated Reducer

Write reduceRequest(state, action) for a request state machine. State is { kind: "idle" } | { kind: "loading" } | { kind: "success", data } | { kind: "error", message }. Actions: { type: "start" } → loading; { type: "resolve", data } → success; { type: "reject", message } → error; { type: "reset" } → idle. RETURN the new state; never mutate.

Difficulty: intermediate