fix(grpcserver): preserve projected gateway listeners

Author: mahmut-Abi

internal/grpcserver/snapshot_projection.go

@@ -157,7 +157,7 @@ func projectListeners(listeners []ir.Listener, snapshot *ir.Snapshot) []ir.Liste
 				attachedRoutes = append(attachedRoutes, routeKey)
 			}
 		}
-		if len(attachedRoutes) == 0 {
+		if len(attachedRoutes) == 0 && !isGatewayProjectedListener(listener) {
 			continue
 		}
 		listener.AttachedRoutes = attachedRoutes
@@ -166,6 +166,13 @@ func projectListeners(listeners []ir.Listener, snapshot *ir.Snapshot) []ir.Liste
 	return out
 }
 
+func isGatewayProjectedListener(listener ir.Listener) bool {
+	if listener.Metadata == nil {
+		return false
+	}
+	return listener.Metadata["gateway"] != "" && listener.Metadata["namespace"] != ""
+}
+
 func filterBackendRefs(routeNamespace string, refs []ir.BackendRef, survivingBackends map[string]struct{}) []ir.BackendRef {
 	out := make([]ir.BackendRef, 0, len(refs))
 	for _, ref := range refs {

internal/grpcserver/snapshot_projection_test.go

@@ -135,6 +135,44 @@ func TestProjectedSnapshotFullProfilePreservesAIServiceTokenPolicyWasmAndLabels(
 	}
 }
 
+func TestProjectedSnapshotPreservesListenerWhenAllAttachedRoutesArePruned(t *testing.T) {
+	t.Parallel()
+
+	projected := buildProjectedProtoSnapshot(
+		&ir.Snapshot{
+			Listeners: []ir.Listener{{
+				Name:           "listener-empty-after-projection",
+				Address:        "0.0.0.0",
+				Port:           80,
+				Protocol:       "HTTP",
+				AttachedRoutes: []string{"default/http-missing"},
+				Metadata: map[string]string{
+					"gateway":   "edge",
+					"namespace": "default",
+				},
+			}},
+			HTTPRoutes: []ir.HTTPRoute{{
+				Name:      "http-missing",
+				Namespace: "default",
+				Rules: []ir.HTTPRule{{
+					BackendRefs: []ir.BackendRef{{
+						Name:      "missing-backend",
+						Namespace: "default",
+						Port:      8080,
+					}},
+				}},
+			}},
+		},
+		effectiveProjectionProfile([]string{featureCoreV1}),
+		slog.New(slog.NewTextHandler(io.Discard, nil)),
+	)
+
+	listener := findProjectedListener(t, projected, "listener-empty-after-projection")
+	if got := listener.GetAttachedRoutes(); len(got) != 0 {
+		t.Fatalf("attached routes = %#v, want empty list", got)
+	}
+}
+
 func projectionTestSnapshot() *ir.Snapshot {
 	return &ir.Snapshot{
 		ID:          "projection-snapshot",