Touch-up codespaces exporting functionality

internal/codespaces/api/api.go

@@ -177,6 +177,7 @@ type CodespaceConnection struct {
 	HostPublicKeys []string `json:"hostPublicKeys"`
 }
 
+// CodespaceFields is the list of exportable fields for a codespace.
 var CodespaceFields = []string{
 	"name",
 	"owner",

pkg/cmd/codespace/ports.go

@@ -158,6 +158,8 @@ func (pi *portInfo) ExportData(fields []string) *map[string]interface{} {
 			data[f] = pi.Label()
 		case "browseUrl":
 			data[f] = pi.BrowseURL()
+		default:
+			panic("unkown field: " + f)
 		}
 	}