fix(operator): StatefulSet 显式保留世界卷，同名旧世界卷仍在时建服回 409 world_volume_exists，文档写明孤儿卷查找与单节点约束

internal/operator/builders.go

@@ -320,6 +320,16 @@ func buildStatefulSet(server *v1alpha1.MinecraftServer, replicas int32, felisIma
 				},
 			},
 			VolumeClaimTemplates: []corev1.PersistentVolumeClaim{pvc},
+			// The world outlives its StatefulSet: deleting the CR (and with it,
+			// by owner reference, the StatefulSet) keeps the claim, so a CR that
+			// comes back under the same name mounts the same world. The reaper is
+			// the one path that deletes a world, after its final backup. Stated
+			// here although it is the API default, so the semantics never ride on
+			// a default.
+			PersistentVolumeClaimRetentionPolicy: &appsv1.StatefulSetPersistentVolumeClaimRetentionPolicy{
+				WhenDeleted: appsv1.RetainPersistentVolumeClaimRetentionPolicyType,
+				WhenScaled:  appsv1.RetainPersistentVolumeClaimRetentionPolicyType,
+			},
 		},
 	}
 	return sts, nil

internal/operator/probes_internal_test.go

@@ -54,3 +54,17 @@ func TestGameContainerProbes(t *testing.T) {
 		t.Fatalf("login-gate startup = %+v", p)
 	}
 }
+
+// Deleting a server's StatefulSet, or scaling it to zero, keeps the world claim.
+func TestWorldClaimOutlivesTheStatefulSet(t *testing.T) {
+	srv := &v1alpha1.MinecraftServer{ObjectMeta: metav1.ObjectMeta{Name: "survival", Namespace: "minecraft"}}
+	srv.Spec.Image = "itzg/minecraft-server:java21"
+	sts, err := buildStatefulSet(srv, 1, "felis:test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	p := sts.Spec.PersistentVolumeClaimRetentionPolicy
+	if p == nil || p.WhenDeleted != "Retain" || p.WhenScaled != "Retain" {
+		t.Fatalf("retention policy = %+v, want Retain on delete and on scale", p)
+	}
+}