Cannot load Scala 2 library TASTy with CC annotations

[nicolasstucki]

Minimized example

// Test.scala
def test: Option[Int] = Some(1)

sbt> set ThisBuild/Build.scala2Library := Build.Scala2LibraryCCTasty
sbt> scala3-bootstrapped/scalac Test.scala

See http://dotty.epfl.ch/docs/contributing/testing.html#scala-2-library-tasty-tests-1 for info on using the Scala 2 TASTy library.

Output

-- Error: Test.scala:1:10 ----------------------------------------------------
1 |def test: Option[Int] = Some(1)
  |          ^
  |Could not read definition class Option in ./scala2-library-cc-tasty/../out/bootstrap/scala2-library-cc-tasty/scala-3.4.0-RC1-bin-SNAPSHOT-nonbootstrapped/scala2-library-cc-tasty_3-3.4.0-RC1-bin-SNAPSHOT.jar(scala/Option.tasty). Caused by the following exception:
  |dotty.tools.dotc.core.UnpicklingError: Could not read definition type IterableOnce in ./scala2-library-cc-tasty/../out/bootstrap/scala2-library-cc-tasty/scala-3.4.0-RC1-bin-SNAPSHOT-nonbootstrapped/scala2-library-cc-tasty_3-3.4.0-RC1-bin-SNAPSHOT.jar(scala/package.tasty). Caused by the following exception:
  |dotty.tools.dotc.core.UnpicklingError: Could not read definition trait IterableOnce in ./scala2-library-cc-tasty/../out/bootstrap/scala2-library-cc-tasty/scala-3.4.0-RC1-bin-SNAPSHOT-nonbootstrapped/scala2-library-cc-tasty_3-3.4.0-RC1-bin-SNAPSHOT.jar(scala/collection/IterableOnce.tasty). Caused by the following exception:
  |dotty.tools.dotc.core.UnpicklingError: Could not read definition trait Iterable in ./scala2-library-cc-tasty/../out/bootstrap/scala2-library-cc-tasty/scala-3.4.0-RC1-bin-SNAPSHOT-nonbootstrapped/scala2-library-cc-tasty_3-3.4.0-RC1-bin-SNAPSHOT.jar(scala/collection/immutable/Iterable.tasty). Caused by the following exception:
  |dotty.tools.dotc.core.UnpicklingError: Could not read definition trait Iterable in ./scala2-library-cc-tasty/../out/bootstrap/scala2-library-cc-tasty/scala-3.4.0-RC1-bin-SNAPSHOT-nonbootstrapped/scala2-library-cc-tasty_3-3.4.0-RC1-bin-SNAPSHOT.jar(scala/collection/Iterable.tasty). Caused by the following exception:
  |dotty.tools.dotc.core.CyclicReference: Cyclic reference involving trait Seq
  |
  |Run with -Ydebug-unpickling to see full stack trace.
1 error found

[odersky]

What needs to be done if the library is changed:

scala2-library-cc/clean
scala2-library-cc-tasty/clean
scala2-library-cc/compile

set ThisBuild/Build.scala2Library := Build.Scala2LibraryCCTasty
scala3-bootstrapped/scalac Test.scala // + options