Maintain normal column layout while editing.

frontend/src/pagerite.js

@@ -269,22 +269,19 @@ import "overlayscrollbars/overlayscrollbars.css";
     // created page has no pen for commitPending's handover click.
     renderAuthUi();
     placeEditPen();
+    // Preview swaps also wipe the .colseg wrappers (the server render has
+    // none), which would drop the multi-column layout until a full reload;
+    // re-split so columns survive both live editing and closing the editor.
+    const main = document.getElementById("main");
+    if (main) applyMulticol(main);
   });
 
-  function applyEffects() {
-    (window.requestIdleCallback || setTimeout)(preload);
-    const main = document.getElementById("main");
-    addCopyButtons(main);
-    // Fetch-navigation swaps #main, discarding the article pen and corner
-    // buttons; re-add whichever auth UI is appropriate for this session.
-    renderAuthUi();
-    placeEditPen();
-    fitNav();
   // Multi-column layout only when there is enough text to justify it.
   // Split the body into columned segments: h1s, h2s and wide figures are
   // full-width separators and never go inside columns.
+  function applyMulticol(main) {
     const article = main.querySelector("article");
-    if (article) {
+    if (!article) return;
     const body = article.querySelector(".body");
     article.classList.toggle(
       "multicol",
@@ -318,6 +315,17 @@ import "overlayscrollbars/overlayscrollbars.css";
       }
     }
   }
+
+  function applyEffects() {
+    (window.requestIdleCallback || setTimeout)(preload);
+    const main = document.getElementById("main");
+    addCopyButtons(main);
+    // Fetch-navigation swaps #main, discarding the article pen and corner
+    // buttons; re-add whichever auth UI is appropriate for this session.
+    renderAuthUi();
+    placeEditPen();
+    fitNav();
+    applyMulticol(main);
     if (reduceMotion.matches) return;
     for (const el of main.querySelectorAll(
       "h2, h3, figure, img, pre, blockquote, table, dl, .task-list-item",