fix: skip completing placeholder on readonly editors

frontend/src/core/codemirror/placeholder/extensions.ts

@@ -1,6 +1,7 @@
 /* Copyright 2024 Marimo. All rights reserved. */
 import type { Extension } from "@codemirror/state";
 import { EditorView, keymap, placeholder } from "@codemirror/view";
+import { isEditorReadonly } from "../readonly/extension";
 
 /**
  * A placeholder that will be shown when the editor is empty and support
@@ -25,6 +26,10 @@ export function smartPlaceholderExtension(text: string): Extension[] {
 }
 
 function acceptPlaceholder(cm: EditorView, text: string) {
+  if (isEditorReadonly(cm.state)) {
+    return false;
+  }
+
   // if empty, insert the placeholder
   const docLength = cm.state.doc.length;
   if (docLength === 0) {

frontend/src/core/network/requests-network.ts

@@ -2,8 +2,9 @@
 
 import { once } from "lodash-es";
 import { getRuntimeManager } from "../runtime/config";
+import { store } from "../state/jotai";
 import { API, createClientWithRuntimeManager } from "./api";
-import { waitForConnectionOpen } from "./connection";
+import { isConnectedAtom, waitForConnectionOpen } from "./connection";
 import type { EditRequests, RunRequests } from "./types";
 
 const { handleResponse, handleResponseReturnNull } = API;
@@ -83,7 +84,11 @@ export function createNetworkRequests(): EditRequests & RunRequests {
         .then(handleResponseReturnNull);
     },
     sendRun: async (request) => {
-      await waitForConnectionOpen();
+      // Rather than waiting, we just drop all sendRun requests if the connection is not open.
+      // Otherwise we can get into a weird state of sending requests for cells that no longer exist.
+      if (!store.get(isConnectedAtom)) {
+        return null;
+      }
       return getClient()
         .POST("/api/kernel/run", {
           body: request,