This is kind of a minimal example of the tags failure. Works with the commented variation.

tabulaInANutshell.scala

import ohnosequences.pointless._, AnyTaggedType._

trait AnyAct {
  type Itm <: AnyTaggedType
  val  itm: Itm

  // type Out[I <: Itm] = Tagged[I]
  type Out = Tagged[Itm]
}

trait AnyExec {
  type Act <: AnyAct
  
  // type O <: Act#Out[Act#Itm]
  type O = Act#Out
  def apply: O
}

class FooExec[F <: AnyAct](act: F)(result: F#Itm#Raw)
    extends AnyExec {

  type Act = F
  // type O = Tagged[F#Itm]

  def apply: O =
    // act.itm =>> result
    (act.itm: F#Itm) =>> result
}