[CAL-4996] better error when required field is required in router but not present

[PeerRich]

currently:

_{From SyncLinear.com | CAL-4996}

[retrogtx]

I assume this error is for the form?

[renderhq]

Hey team 👋

Just linking back for clarity this PR #22050 fixes the issue mentioned here (#18529 / CAL-4996) by returning structured JSON responses, proper HTTP status codes (400, 409, 500), and handling edge cases more gracefully.

Let me know if you'd like any changes or clarification.
Appreciate the review!

Thanks 🙌