Fix the Steppable CEK machine to correctly "pause/step" in case of SO…

…Ps. (#6790)

Co-authored-by: Nikolaos Bezirgiannis <[email protected]>

plutus-core/changelog.d/20250114_110640_bezirg_steppable_sop_fix.md

@@ -0,0 +1,3 @@
+### Fixed
+
+- Fix the Steppable CEK machine to correctly "pause/step" in case of SOPs.

plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Evaluation/Machine/SteppableCek/Internal.hs

@@ -157,13 +157,13 @@ computeCek !ctx !_ (Builtin _ bn) = do
 -- s ; ρ ▻ constr I T0 .. Tn  ↦  s , constr I _ (T1 ... Tn, ρ) ; ρ ▻ T0
 computeCek !ctx !env (Constr ann i es) = do
     stepAndMaybeSpend BConstr
-    case es of
-        (t : rest) -> computeCek (FrameConstr ann env i rest EmptyStack ctx) env t
-        []         -> returnCek ctx $ VConstr i EmptyStack
+    pure $ case es of
+        (t : rest) -> Computing (FrameConstr ann env i rest EmptyStack ctx) env t
+        []         -> Returning ctx $ VConstr i EmptyStack
 -- s ; ρ ▻ case S C0 ... Cn  ↦  s , case _ (C0 ... Cn, ρ) ; ρ ▻ S
 computeCek !ctx !env (Case ann scrut cs) = do
     stepAndMaybeSpend BCase
-    computeCek (FrameCases ann env cs ctx) env scrut
+    pure $ Computing (FrameCases ann env cs ctx) env scrut
 -- s ; ρ ▻ error A  ↦  <> A
 computeCek !_ !_ (Error _) =
     throwing_ _EvaluationFailure