Set exittype for error exit as well as the error string.

client.c

@@ -219,9 +219,12 @@ client_main(struct client_ctx *cctx)
 	case CCTX_DETACH:
 		printf("[detached]\n");
 		return (0);
-	default:
+	case CCTX_ERROR:
 		printf("[error: %s]\n", cctx->errstr);
 		return (1);
+	default:
+		printf("[error: unknown error]\n");
+		return (1);
 	}
 }
 
@@ -275,6 +278,7 @@ client_msg_dispatch(struct client_ctx *cctx)
 
 			printdata.msg[(sizeof printdata.msg) - 1] = '\0';
 			cctx->errstr = xstrdup(printdata.msg);
+			cctx->exittype = CCTX_ERROR;
 			imsg_free(&imsg);
 			return (-1);
 		case MSG_EXIT:

tmux.h

@@ -974,6 +974,7 @@ struct client_ctx {
 		CCTX_EXIT,
 		CCTX_DIED,
 		CCTX_SHUTDOWN,
+		CCTX_ERROR
 	} exittype;
 	const char	*errstr;
 };