Caqti and unique violation error

Learning
1

I have a function that returns ('a, Caqti_error.t) result and I’m trying to catch unique violation error

  | Ok _ -> ....
  | Error err -> (
      match err with
      | `Response_failed err -> (
          let cause = `Response_failed err |> Caqti_error.cause in
          match cause with
          | `Integrity_constraint_violation__don't_match ->
              print_string "intercepted!"
          | _ -> ())
      | _ -> ())

After launching I see in the console “intercepted!”, Am I doing the type narrowing correctly? Why is the uniqueness error in Response_failed and not in Request_failed? Or is this a feature of the sqlite3 driver?