Derived Configs for a sealed trait does not search for other implicits

[steinybot]

Implicits are not resolved when automatically deriving Configs for a sealed trait:

case class A1(b: B1)

object A1 {

  implicit val cConfigs: Configs[C1] = {
    (c, _) => c.get[String]("d").map(C1.make)
  }
  implicit val bConfigs: Configs[B1] = Configs.autoDeriveConfigs[B1]
  implicit val aConfigs: Configs[A1] = Configs.autoDeriveConfigs[A1]
}

sealed trait B1

class C1 private(val d: String) extends B1

object C1 {

  def make(d: String): C1 = new C1(d)
}

This fails with:

[error] C1 has no public constructor
[error]   implicit val bConfigs: Configs[B1] = Configs.autoDeriveConfigs[B1]
[error]                                                                 ^

The simple case works:

case class A2(b: B2)

object A2 {

  implicit val aConfigs: Configs[A2] = Configs.autoDeriveConfigs[A2]
}

sealed trait B2

case class C2(d: String) extends B2

We can show that implicits are resolved when automatically deriving Configs for a case class:

case class A3(b: C3)

object A3 {

  implicit val cConfigs: Configs[C3] = {
    (c, _) => c.get[String]("d").map(C3.make)
  }
  implicit val aConfigs: Configs[A3] = Configs.autoDeriveConfigs[A3]
}

class C3 private(val d: String)

object C3 {

  def make(d: String): C3 = new C3(d)
}