anchor.diff:                  GotoActions = GotoActions.ToImmutable()
               }
   
  -        let itemTry (arr: ImmutableArray.Builder<_>) idx =
  +        let itemTry (arr: ImmutableArray<_>.Builder) idx =
               let idx = int idx
               if idx < arr.Count then
                   arr.[idx]
               else
                   invalidEGT()
   
  -        let readAndAssignIndexed fRead (arr: ImmutableArray.Builder<_>) mem =
  +        let readAndAssignIndexed fRead (arr: ImmutableArray<_>.Builder) mem =
               lengthMustBeAtLeast mem 1
               let index = wantUInt16 mem 0
               let content = mem.Slice(1)
  
positive.code:             | AnyGroupEnd of GroupEnd
              | AnyError
  
          let createSafeIndexed<'a> (arr: ImmutableArray.Builder<'a>) idx =
              if int idx <= arr.Capacity then
                  idx |> uint32
              else
  
negative.code:             | 7us -> AnyError
              | _ -> invalidEGT()
  
          let readGroup (symbols: ImmutableArray<_>.Builder) fSymbol fGroup index mem =
              lengthMustBeAtLeast mem 7
              let name = wantString mem 0
              let container = wantUInt16 mem 1 |> fSymbol |> wantGroupContainer
  