Replace split textarea/preview editor with a single CodeMirror Markdown editor

tests/selftest-scenario.js

@@ -82,6 +82,33 @@ const BOOK_DIR = __BOOKDIR_VALUE__;
     out.uiCreated = metaAfterUi.chapterOrder.length === countBefore + 1 &&
       Object.values(metaAfterUi.chapters).some((c) => c.title === "Via Modal");
 
+    // CodeMirror editor: typing, cursor/selection, autosave persistence
+    const cm = window.__folioEditor;
+    out.hasEditor = !!cm;
+    out.editorLoaded = cm ? cm.state.doc.toString() : null;
+    if (cm) {
+      cm.dispatch({
+        changes: {
+          from: 0,
+          to: cm.state.doc.length,
+          insert: "# Heading One\n\n**bold** and *italic* text\n\n- bullet one\n- bullet two\n\n> quoted line\n\n[link](https://example.com) and `inline code`\n\n---",
+        },
+      });
+      cm.dispatch({ selection: { anchor: cm.state.doc.length } });
+    }
+    await new Promise((r) => setTimeout(r, 1200));
+    out.editorDocAfterType = cm ? cm.state.doc.toString() : null;
+    const typedId = metaAfterUi.chapterOrder[metaAfterUi.chapterOrder.length - 1];
+    const typedContent = await window.folio.getChapterContent(typedId);
+    out.editorAutosaved =
+      !!cm &&
+      cm.state.doc.toString().includes("**bold** and *italic*") &&
+      typedContent.includes("# Heading One") &&
+      typedContent.includes("- bullet two") &&
+      typedContent.includes("> quoted line") &&
+      typedContent.includes("[link](https://example.com)") &&
+      typedContent.includes("`inline code`");
+
     out.all = true;
   } catch (e) {
     out.error = String((e && e.message) || e);