diff --git a/R/app.R b/R/app.R
index 2f21832a..2aa1d1d2 100644
--- a/R/app.R
+++ b/R/app.R
@@ -35,24 +35,6 @@ configure_logger <- function() {
   }
 }
 
-load_main_module <- function() {
-  # Silence "no visible binding" notes raised by `box::use()` on R CMD check.
-  app <- NULL
-  main <- NULL
-  box::use(app/main)
-  main
-}
-
-as_top_level <- function(app_env) {
-  list(
-    # Wrap the UI in a function to support Shiny bookmarking.
-    ui = function(request) app_env$main$ui("app"),
-    server = fix_server_reloading(function(input, output) {
-      app_env$main$server("app")
-    })
-  )
-}
-
 fix_server_reloading <- function(server) {
   reparse(curly_wrap(server))
 }
@@ -124,6 +106,24 @@ with_head_tags <- function(ui) {
   }
 }
 
+call_ui <- function(ui, request) {
+  if (!is.function(ui)) {
+    ui
+  } else if (length(formals(ui)) == 0) {
+    ui()
+  } else {
+    ui(request)
+  }
+}
+
+call_server <- function(server, input, output, session) {
+  if ("session" %in% formalArgs(server)) {
+    server(input, output, session)
+  } else {
+    server(input, output)
+  }
+}
+
 #' Rhino application
 #'
 #' The entrypoint for a Rhino application.
@@ -170,7 +170,6 @@ with_head_tags <- function(ui) {
 #' @export
 app <- function() {
   setup_box_path()
-  box::purge_cache()
   configure_logger()
   shiny::addResourcePath("static", fs::path_wd("app", "static"))
 
@@ -185,17 +184,27 @@ app <- function() {
       server = main$server
     )
   } else if (identical(entrypoint, "box_top_level")) {
-    main <- load_main_module()
+    app_env <- load_app()
+    ui <- function(request) {
+      call_ui(app_env$main$ui, request)
+    }
+    server <- function(input, output, session) {
+      call_server(app_env$main$server, input, output, session)
+    }
     shiny::shinyApp(
-      ui = with_head_tags(main$ui),
-      server = main$server
+      ui = with_head_tags(ui),
+      server = reparse(server)
     )
   } else if (is.null(entrypoint)) {
     app_env <- load_app()
-    main <- as_top_level(app_env)
+    # Wrap the UI in a function to support Shiny bookmarking.
+    ui <- function(request) app_env$main$ui("app")
+    server <- function(input, output) {
+      app_env$main$server("app")
+    }
     shiny::shinyApp(
-      ui = with_head_tags(main$ui),
-      server = main$server
+      ui = with_head_tags(ui),
+      server = fix_server_reloading(server)
     )
   } else {
     stop()