fix(substrate): degrade gracefully when ate.dev CRDs are absent

GET /api/substrate/status returned 500 on clusters without the agent-substrate
CRDs installed because listSubstrateCRs propagated the REST mapper NoKindMatchError
as a server error. Treat IsNoMatchError as an empty result so the endpoint returns
200 with Enabled:false when substrate is not configured.

Signed-off-by: QuentinBisson <quentin@giantswarm.io>

Author: QuentinBisson

go/core/internal/httpserver/handlers/substrate.go

@@ -13,6 +13,7 @@ import (
 	"github.com/kagent-dev/kagent/go/core/internal/httpserver/errors"
 	"github.com/kagent-dev/kagent/go/core/pkg/auth"
 	"github.com/kagent-dev/kagent/go/core/pkg/sandboxbackend/substrate"
+	"k8s.io/apimachinery/pkg/api/meta"
 	utilvalidation "k8s.io/apimachinery/pkg/util/validation"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 	ctrllog "sigs.k8s.io/controller-runtime/pkg/log"
@@ -110,10 +111,16 @@ func (h *SubstrateHandler) listSubstrateCRs(ctx context.Context, namespace strin
 
 	wpList := &atev1alpha1.WorkerPoolList{}
 	if err := h.KubeClient.List(ctx, wpList, listOpts...); err != nil {
+		if meta.IsNoMatchError(err) {
+			return nil, nil, nil
+		}
 		return nil, nil, err
 	}
 	tmplList := &atev1alpha1.ActorTemplateList{}
 	if err := h.KubeClient.List(ctx, tmplList, listOpts...); err != nil {
+		if meta.IsNoMatchError(err) {
+			return nil, nil, nil
+		}
 		return nil, nil, err
 	}
 

go/core/internal/httpserver/handlers/substrate_test.go

@@ -16,13 +16,50 @@ import (
 	"github.com/stretchr/testify/require"
 	"google.golang.org/grpc"
 	corev1 "k8s.io/api/core/v1"
+	apimeta "k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
 	clientgoscheme "k8s.io/client-go/kubernetes/scheme"
+	"sigs.k8s.io/controller-runtime/pkg/client"
 	"sigs.k8s.io/controller-runtime/pkg/client/fake"
 )
 
+// noMatchKubeClient is a minimal client.Client stub whose List always returns
+// a *meta.NoKindMatchError, simulating a cluster where the listed CRDs are absent.
+type noMatchKubeClient struct {
+	client.Client
+}
+
+func (noMatchKubeClient) List(_ context.Context, _ client.ObjectList, _ ...client.ListOption) error {
+	return &apimeta.NoKindMatchError{}
+}
+
+// TestHandleGetSubstrateStatus_NoCRDs verifies that the endpoint returns 200 with
+// Enabled:false and empty slices when the ate.dev CRDs are not installed on the cluster.
+func TestHandleGetSubstrateStatus_NoCRDs(t *testing.T) {
+	t.Parallel()
+
+	// AteClient is nil — substrate is not configured.
+	base := &handlers.Base{KubeClient: noMatchKubeClient{}, Authorizer: &auth.NoopAuthorizer{}}
+	h := handlers.NewSubstrateHandler(base, nil)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/substrate/status?namespace=kagent", nil)
+	req = setUser(req, "test-user")
+	rec := httptest.NewRecorder()
+	h.HandleGetSubstrateStatus(&testErrorResponseWriter{ResponseWriter: rec}, req)
+
+	require.Equal(t, http.StatusOK, rec.Code)
+
+	var wrapped api.StandardResponse[api.SubstrateStatusResponse]
+	require.NoError(t, json.Unmarshal(rec.Body.Bytes(), &wrapped))
+	require.False(t, wrapped.Data.Enabled)
+	require.Empty(t, wrapped.Data.WorkerPools)
+	require.Empty(t, wrapped.Data.ActorTemplates)
+	require.Empty(t, wrapped.Data.Actors)
+	require.Empty(t, wrapped.Data.Workers)
+}
+
 type stubAteControl struct {
 	ateapipb.ControlClient
 	actors  []*ateapipb.Actor