docs(react): add Action constraint to redux middleware signature

[TheSeydiCharyyev]

The redux middleware signature in the reference docs is missing the Action constraint that's present in src/middleware/redux.ts:

// src/middleware/redux.ts
type Action = { type: string }

type Redux = <
  T,
  A extends Action,    // ← constraint
  Cms extends [StoreMutatorIdentifier, unknown][] = [],
>(
  reducer: (state: T, action: A) => T,
  initialState: T,
) => StateCreator<Write<T, ReduxState<A>>, Cms, [['zustand/redux', A]]>

Without the constraint, the docs allow A to be any type. With the constraint, TypeScript enforces that action.type is accessible — which is the whole point of the redux pattern (action discriminator).

Diff

- redux<T, A>(reducerFn: (state: T, action: A) => T, initialState: T): StateCreator<T & { dispatch: (action: A) => A }, [['zustand/redux', A]], []>
+ redux<T, A extends { type: string }>(reducerFn: (state: T, action: A) => T, initialState: T): StateCreator<T & { dispatch: (action: A) => A }, [['zustand/redux', A]], []>

Single change: <T, A> → <T, A extends { type: string }>.

This is part of an ongoing pass over the reference docs to align signatures with source — see #3487, #3489, #3491.

Docs-only — no changeset needed.

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Project	Deployment	Actions	Updated (UTC)
zustand-demo	Ready	Preview, Comment	May 19, 2026 11:48am

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