Small fixes

op-challenger/game/fault/solver/solver.go

@@ -108,10 +108,9 @@ func (s *claimSolver) AttemptStep(ctx context.Context, game types.Game, claim ty
 			return StepData{}, err
 		}
 	} else {
-		// We agree with the claim so Defend and use this claim as the starting point to execute the step after
-		// Thus we need the pre-state of the next step
-		defendingPosition := types.NewPosition(s.gameDepth, int(claim.TraceIndex(s.gameDepth))+1)
-		preState, proofData, oracleData, err = s.trace.GetStepData(ctx, defendingPosition)
+		// We agree with the claim so Defend and use this claim as the starting point to
+		// execute the step after. Thus we need the pre-state of the next step.
+		preState, proofData, oracleData, err = s.trace.GetStepData(ctx, claim.NextStepPosition(s.gameDepth))
 		if err != nil {
 			return StepData{}, err
 		}

op-challenger/game/fault/types/position.go

@@ -18,6 +18,13 @@ func NewPositionFromGIndex(x uint64) Position {
 	return NewPosition(depth, int(indexAtDepth))
 }
 
+func (p Position) NextStepPosition(gameDepth int) Position {
+	return Position{
+		depth:        gameDepth,
+		indexAtDepth: int(p.TraceIndex(gameDepth) + 1),
+	}
+}
+
 func (p Position) Depth() int {
 	return p.depth
 }