Hii @BittuChan, thanks for writing it up so clearly. I ran into this exact problem migrating a Next.js app from v3 to v4. I had cross-field validation everywhere password confirmations, date range pickers, conditional required fields based on a toggle and all of it broke overnight when ctx.parent was removed.

What I tried (and why each fell short):

• Object-level .superRefine() - Works for validation logic, but React Hook Form maps errors by field path. When the error lives on the parent object, the individual field doesn't show it. We had to write custom error-mapping glue code that felt wrong.
• Splitting validation into Zod + manual checks - Ended up with validation logic in two places. Bugs crept in because the Zod schema said the form was valid but our manual check disagreed.
• Using .transform() to sneak in validation - Technically works but it's a hack. Transforms are for data shaping, not validation, and it makes the schema harder to read.

Why I think the dependsOn API is the right direction:
The dependsOn approach from the proposal is interesting because it makes the dependency between fields explicit and declarative. The validation engine could use that information to:

• Run dependent validations only after the dependency field passes
• Produce field-level errors that form libraries can map correctly
• Keep the schema readable so that anyone looking at it immediately understands the relationship

That said, I'd add one thing to the proposal which is support for depending on multiple fields:

const schema = z.object({
role: z.enum(["admin", "user"]),
department: z.string(),
accessLevel: z.number().dependsOn(
["role", "department"],
(level, role, dept) => {
if (role === "user" && dept !== "engineering") return level <= 3;
return true;
},
{ message: "Access level too high for this role/department combination" }
),
});