Return 409 Conflict for duplicate email registration
Duplicate email registration now returns 409 Conflict with a dedicated AUTH_EMAIL_EXISTS error code. Previously, all registration failures returned 400 Bad Request with AUTH_REGISTRATION_FAILED, forcing callers to pattern-match on the details string to detect duplicates.
Callers can now match on the code field directly:
{ "code": "AUTH_EMAIL_EXISTS", "message": "A user with this email already exists.", "details": null, "hint": "Try logging in instead."}Other registration failures continue to return 400 with AUTH_REGISTRATION_FAILED.
For the full error code reference, see User Tokens — Error Codes.