UI-tests und fixes aus tests

public/js/modules/editor.js

@@ -232,7 +232,8 @@ function getMirror() {
     mirror.style.paddingRight = cs.paddingRight;
     mirror.style.borderLeft = cs.borderLeft;
     mirror.style.borderRight = cs.borderRight;
-    mirror.style.width = body.offsetWidth + 'px';
+    // Use clientWidth to exclude scrollbar, matching the actual text flow area
+    mirror.style.width = body.clientWidth + 'px';
     return mirror;
 }
 
@@ -260,12 +261,16 @@ function updateGutter() {
     sentinel.textContent = '\u200b';
     m.appendChild(sentinel);
 
+    // Use the first short line's height as the base line height
+    const baseH = divs[0] ? (divs.length > 1 ? divs[1].offsetTop - divs[0].offsetTop : sentinel.offsetTop - divs[0].offsetTop) : 22;
+
     let html = '';
     for (let i = 0; i < divs.length; i++) {
         const top = divs[i].offsetTop;
         const nextTop = (i + 1 < divs.length) ? divs[i + 1].offsetTop : sentinel.offsetTop;
         const h = nextTop - top;
-        html += `<div style="height:${h}px" class="${i + 1 === active ? 'gutter-active' : ''}">${i + 1}</div>`;
+        // Outer div: exact height, no line-height influence. Inner span: base line-height so number sits on first line.
+        html += `<div style="display:block;height:${h}px;line-height:0;overflow:hidden" class="${i + 1 === active ? 'gutter-active' : ''}"><span style="display:inline-block;line-height:${baseH}px">${i + 1}</span></div>`;
     }
     gutter.innerHTML = html;
     currentLine = active;