Add IsDuplicate to game state (#6173)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

op-challenger/fault/agent.go

@@ -49,9 +49,8 @@ func (a *Agent) move(claim, parent Claim) error {
 	if err != nil || move == nil {
 		return err
 	}
-	// TODO(CLI-4123): Don't send duplicate responses
-	// if a.game.IsDuplicate(move) {
-	// 	return nil
-	// }
+	if a.game.IsDuplicate(*move) {
+		return nil
+	}
 	return a.responder.Respond(context.TODO(), *move)
 }

op-challenger/fault/game.go

@@ -22,6 +22,8 @@ type Game interface {
 		claim  Claim
 		parent Claim
 	}
+
+	IsDuplicate(claim Claim) bool
 }
 
 // Node is a node in the game state tree.
@@ -33,17 +35,21 @@ type Node struct {
 // gameState is a struct that represents the state of a dispute game.
 // The game state implements the [Game] interface.
 type gameState struct {
-	root Node
+	root   Node
+	claims map[ClaimData]Claim
 }
 
 // NewGameState returns a new game state.
 // The provided [Claim] is used as the root node.
 func NewGameState(root Claim) *gameState {
+	claims := make(map[ClaimData]Claim)
+	claims[root.ClaimData] = root
 	return &gameState{
 		root: Node{
 			self:     root,
 			children: make([]*Node, 0),
 		},
+		claims: claims,
 	}
 }
 
@@ -116,10 +122,16 @@ func (g *gameState) Put(claim Claim) error {
 
 	// Add the node to the tree.
 	found.children = append(found.children, &node)
+	g.claims[claim.ClaimData] = claim
 
 	return nil
 }
 
+func (g *gameState) IsDuplicate(claim Claim) bool {
+	_, ok := g.claims[claim.ClaimData]
+	return ok
+}
+
 // recurseTreePairs recursively walks down the tree from the root node
 // returning a list of claim and parent pairs.
 func (g *gameState) recurseTreePairs(current *Node) []struct {

op-challenger/fault/game_test.go

@@ -35,6 +35,21 @@ func createTestClaims() (Claim, Claim, Claim) {
 	return top, middle, bottom
 }
 
+func TestIsDuplicate(t *testing.T) {
+	// Setup the game state.
+	top, middle, bottom := createTestClaims()
+	g := NewGameState(top)
+	err := g.Put(middle)
+	require.NoError(t, err)
+
+	// Top + Middle should be duplicates
+	require.True(t, g.IsDuplicate(top))
+	require.True(t, g.IsDuplicate(middle))
+
+	// Bottom should not be a duplicate
+	require.False(t, g.IsDuplicate(bottom))
+}
+
 // TestGame_Put_RootAlreadyExists tests the [Game.Put] method using a [gameState]
 // instance errors when the root claim already exists in state.
 func TestGame_Put_RootAlreadyExists(t *testing.T) {