useMediatedState

Requirements

• Export useMediatedState(mediator, initialState) as named and default. Return a [state, setState] tuple. mediator(nextValue, previousValue) returns the value to commit.
• The initial state is stored unchanged and is not passed through the mediator. Support lazy initialization with a pure function. Later initialState argument changes do not reset the state.
• The setter accepts a value or pure functional updater. Resolve an updater against the latest pending state, then mediate its result against that same previous state.
• Batched updates compose sequentially using mediated values, avoiding stale closures. A mediator can normalize, clamp, or reject an update by returning the previous value.
• The setter identity remains stable. After mediator changes on a rerender, even an earlier saved setter uses the latest mediator for subsequent updates.
• Keep instances independent. Initializers, updaters, and mediators must be pure because React Strict Mode may repeat them. Function-valued state, asynchronous mediation, and update callbacks are outside scope.

Examples

Input: const [count, setCount] = useMediatedState(
  next => Math.max(0, Math.min(10, next)),
  0,
);
setCount(20);
Output: The next state is 10.

Input: const [value, setValue] = useMediatedState(
  (next, previous) => next < previous ? previous : next,
  5,
);
setValue(3);
Output: The mediator rejects the decrease, leaving state at 5.