Walk me through how you would build a multi step form with validation and the ability to resume.

Keep one schema for the whole form and validate each step against its slice, so the same rules run on the client and again on the server. Hold answers in a single object above the steps, drive the current step from the URL so back and forward work, and persist progress on step change. Validate on blur and on submit, and never trust client validation as the only gate.

I start with a single schema for the whole thing, then each step validates its own slice of it. That way there is one definition of what valid means, and I can run the exact same schema on the server, because client validation is a convenience and not a guarantee. The collected answers live in one object in a parent, or a small store if the steps are far apart in the tree, and each step gets its slice and a way to write back. The current step goes in the URL, which sounds like a detail but it fixes several things at once: back and forward work, someone can refresh without losing their place, and support can ask which URL they are on. I persist the draft on each step transition, usually to the server if the user is signed in and to storage if not. Validation runs on blur and again on next, and on final submit I handle server errors by mapping the field paths back to the right step and jumping the user there with focus on the offending input.