$ dune build
Internal error, please report upstream including the contents of _build/log.
Description:
  ("Unexpected find result", { found = Not_found; lib.name = "lib_core" })
Raised at Stdune__code_error.raise in file "otherlibs/stdune/code_error.ml",
  line 11, characters 30-62
Called from Fiber__scheduler.exec in file "src/fiber/scheduler.ml", line 69,
  characters 8-11
-> required by ("<unnamed>", ())
-> required by ("<unnamed>", ())
-> required by ("<unnamed>", ())
-> required by ("load-dir", In_build_dir "default/bin")
-> required by ("<unnamed>", ())
-> required by ("build-alias", { dir = "default"; name = "default" })
-> required by ("toplevel", ())

I must not crash.  Uncertainty is the mind-killer. Exceptions are the
little-death that brings total obliteration.  I will fully express my cases.
Execution will pass over me and through me.  And when it has gone past, I
will unwind the stack along its path.  Where the cases are handled there will
be nothing.  Only I will remain.