React async validation: the late answer problem
An earlier input can return after a later one. Example: 'taken' takes 900 ms; 'fast' takes 180 ms. If both responses blindly set the same error state, the old error can appear after the newer valid response. Network cancellation helps but does not replace a generation check.
Reproduce in the kit preview
1. Select Developer and Just me on the onboarding Workspace step. 2. Type taken into Workspace handle and leave the input to start a check. 3. Immediately replace it with fast and click Continue. 4. The latest valid input should reach Profile; the old response cannot commit. 5. With taken left unchanged, Continue should keep you at Workspace with an error.
LatestValidation increments a generation on edit/start, aborts an older check, and labels responses current only when their generation still matches. Callers must check current before changing error state or moving steps. A current thrown check error stays an infrastructure failure, rather than silently passing.
The free sample includes this guard under MIT, with a tiny browser demonstration whose mock deliberately ignores cancellation. It is independently usable; no checkout, registration or React dependency is required for that sample.
Other deliberate failures
At the last step, select Reject a field in the right-side Mock response control. Submit and follow the error-summary link. Inputs remain in memory. Change the field, select Accept request, and submit again. Rejected email sends onboarding back to Profile; the survey's rejected friction goes back to Workflow.
Connection failure preserves the inputs and enables retry. Slow request enables Cancel request. Cancellation means this UI ignores the old result; it does not prove a real server stopped. The preview mocks perform no server writes.
Save preferences, Reset inputs, then Restore preferences. Only allowed select choices return, beginning at step 1; name/email/handle/notes/consent are empty. Reload is not automatic restoration; you explicitly choose Restore preferences. Discard saved draft deletes the selected flow's draft, leaving unrelated storage.
What the free alternatives already do
Free multi-step and draft-persistence libraries exist. W3C guidance explains multi-page forms and error notifications. This kit's paid hypothesis is that a developer values complete editable example flows plus tests and adapter notes. It is not the invention of async validation or proof that buyers will pay.
Primary guidance/research, reviewed 11 October 2026: - https://www.w3.org/WAI/tutorials/forms/multi-page/ - https://www.w3.org/WAI/tutorials/forms/notifications/ - https://github.com/react-hook-form/react-hook-form/issues/10078 (historical, closed report; not a claim that the current library has this defect) - https://github.com/srdjan/react-multistep - https://github.com/mayrang/formdraft
Read INTEGRATION.md before replacing mocks with a real adapter. Browser-only checks are not server security, accessibility certification or guaranteed sales.