diff --git a/internal/web/static/app.css b/internal/web/static/app.css
index 16a77c1..8c2b963 100644
--- a/internal/web/static/app.css
+++ b/internal/web/static/app.css
@@ -319,8 +319,10 @@ html[data-wrap] .float { overflow-x: hidden; }
 .codebody { padding: 0 18px; white-space: pre; overflow-x: auto; }
 /* #167: each logical line is its own block so offsetTop identifies its first visual row */
 .codeline { display: block; }
-/* #167 rev: gutter number spans must stack one per visual row (wrap on) */
-.code .gutter .gutline { display: block; }
+/* #167: gutter number spans must stack one per visual row (wrap on).
+   #274: the /new editor gutter uses the same .gutline blocks when its own
+   wrap toggle is on, so scope the rule to any gutter, not just .code. */
+.code .gutter .gutline, .editor-wrap .gutter .gutline { display: block; }
 /* #194: codeline blocks are adjacent (no '\n' text between them), so an
    empty block (blank source line) needs its own line box to stay one row */
 .codeline:empty::before { content: "\200B"; }
diff --git a/internal/web/static/new.js b/internal/web/static/new.js
index 0782762..3b4453f 100644
--- a/internal/web/static/new.js
+++ b/internal/web/static/new.js
@@ -2,13 +2,71 @@
 const $ = id => document.getElementById(id);
 const content = $('content'), gutter = $('gutter');
 
+// #274: with wrap on, a logical line occupies several VISUAL rows in the
+// textarea, so one number per logical line drifts off its text (same bug the
+// paste view fixed in #167). A textarea can't be split into spans, so the
+// wrapped row count per logical line is measured with a hidden mirror div
+// that shares the editor's font, line metrics and wrapping rules, and the
+// gutter renders one .gutline block per visual row with the number on the
+// FIRST row of its logical line (fillers elsewhere).
+let mirror = null;
+function measureRows(lines) {
+  if (!mirror) {
+    mirror = document.createElement('div');
+    mirror.style.position = 'absolute';
+    mirror.style.visibility = 'hidden';
+    mirror.style.top = '0';
+    mirror.style.left = '-9999px';
+    document.body.appendChild(mirror);
+  }
+  const cs = getComputedStyle(content);
+  mirror.style.font = cs.font;
+  mirror.style.lineHeight = cs.lineHeight;
+  mirror.style.whiteSpace = 'pre-wrap';
+  mirror.style.overflowWrap = 'anywhere';
+  mirror.style.wordBreak = 'break-all';
+  mirror.style.width = (content.clientWidth - parseFloat(cs.paddingLeft) - parseFloat(cs.paddingRight)) + 'px';
+  const lh = parseFloat(cs.lineHeight) || 1;
+  const starts = [];
+  let total = 0;
+  const n = Math.max(lines.length, 1);
+  for (let i = 0; i < n; i++) {
+    // A trailing newline yields an empty last line: it still occupies one row.
+    mirror.textContent = lines[i] + '\n';
+    let rows = Math.max(1, Math.round(mirror.getBoundingClientRect().height / lh));
+    starts.push(total);
+    total += rows;
+  }
+  return { starts, total };
+}
+
 function updateGutter() {
-  const lines = content.value.split('\n').length;
-  let s = '';
-  for (let i = 1; i <= Math.max(lines, 1); i++) s += i + '\n';
-  gutter.textContent = s;
+  const lines = content.value.split('\n');
+  const n = Math.max(lines.length, 1);
+  if (!document.documentElement.hasAttribute('data-wrap')) {
+    let s = '';
+    for (let i = 1; i <= n; i++) s += i + '\n';
+    gutter.textContent = s.slice(0, -1);
+    return;
+  }
+  const { starts, total } = measureRows(lines);
+  gutter.textContent = '';
+  const frag = document.createDocumentFragment();
+  const spans = [];
+  for (let r = 0; r < total; r++) {
+    const c = document.createElement('span');
+    c.className = 'gutline';
+    c.textContent = '\u00a0';
+    spans.push(c);
+    frag.appendChild(c);
+  }
+  gutter.appendChild(frag);
+  for (let j = 0; j < starts.length; j++) spans[starts[j]].textContent = String(j + 1);
 }
 content.addEventListener('input', updateGutter);
+// #274: the wrap toggle and width changes re-wrap the textarea; re-measure.
+new MutationObserver(updateGutter).observe(document.documentElement, { attributes: true, attributeFilter: ['data-wrap'] });
+window.addEventListener('resize', updateGutter);
 // #259: the editor scrolls itself; keep the gutter's numbers in step with it.
 content.addEventListener('scroll', () => { gutter.scrollTop = content.scrollTop; });
 updateGutter();