diff --git a/internal/verify/replay_determinism_test.go b/internal/verify/replay_determinism_test.go
new file mode 100644
index 0000000..d955557
--- /dev/null
+++ b/internal/verify/replay_determinism_test.go
@@ -0,0 +1,48 @@
+package verify
+
+import (
+	"path/filepath"
+	"testing"
+
+	snapshotpkg "digiemu-core/pkg/snapshot"
+)
+
+func TestReplayV1Idempotent(t *testing.T) {
+	root := repoRoot(t)
+
+	fixtureRoot := filepath.Join(root, "data", "test-fixtures")
+	dataRoot := filepath.Join(root, "data")
+
+	bundleRoot, _, err := FindBundleRoot("demo", fixtureRoot, dataRoot, false)
+	if err != nil {
+		t.Fatalf("FindBundleRoot: %v", err)
+	}
+
+	bundle, _, err := LoadBundleRootV1(bundleRoot)
+	if err != nil {
+		t.Fatalf("LoadBundleRootV1: %v", err)
+	}
+
+	var first snapshotpkg.HashV1
+
+	for i := 0; i < 10; i++ {
+		replayed, err := ReplayV1(bundle, []string{"test-replay-idempotent"})
+		if err != nil {
+			t.Fatalf("ReplayV1 iteration %d: %v", i, err)
+		}
+
+		hash, err := snapshotpkg.HashV1FromState(replayed.StateV1)
+		if err != nil {
+			t.Fatalf("HashV1FromState iteration %d: %v", i, err)
+		}
+
+		if i == 0 {
+			first = hash
+			continue
+		}
+
+		if hash != first {
+			t.Fatalf("ReplayV1 must be idempotent: iteration 0 hash=%s iteration %d hash=%s", first, i, hash)
+		}
+	}
+}