diff --git a/internal/web/static/paste-lines.js b/internal/web/static/paste-lines.js
index 0eac3d3..98eda6a 100644
--- a/internal/web/static/paste-lines.js
+++ b/internal/web/static/paste-lines.js
@@ -1,7 +1,13 @@
 // #167: with line wrapping on, a logical line can occupy several visual
-// lines; the gutter must show one number per VISUAL line. Per-line spans
-// give each logical line its own box so offsetTop order stays correct even
-// when highlighting spans cross no line boundaries.
+// lines; the gutter must show one number per logical line, aligned with its
+// FIRST visual row, and blank rows below it so later numbers don't drift.
+//
+// Row accounting must be based on actual rendered geometry, not per-span
+// height: in a pre-wrap container the newline text nodes BETWEEN the
+// .codeline blocks each render as their own anonymous-block row, so a
+// logical line's visual footprint is (next line's top - this line's top),
+// not this line's own box height. Measuring the gap between consecutive
+// line tops captures both the wrapped rows and the newline row.
 (function () {
   var body = document.getElementById('codebody');
   var gutter = document.getElementById('gutter');
@@ -28,21 +34,32 @@
     var lines = body.querySelectorAll('.codeline');
     var s = '';
     if (wrapOn() && lines.length) {
-      // Each logical line block occupies rows = height / line-height when
-      // wrapped; its number sits on the first row and the remaining rows get
-      // blank gutter lines so numbers stay aligned with line starts.
-      // The code column width must not change while measuring (the gutter is
-      // flex-shrink:0 so its own row count never affects it), and renumber
-      // must be idempotent to avoid a ResizeObserver feedback loop.
+      // Rows per logical line = rendered vertical gap to the next line's
+      // first row (wrapped rows + the pre-wrap newline row between blocks),
+      // divided by line-height. The last line has no following newline, so
+      // its own box height is correct. The code column width must not
+      // change while measuring (the gutter is flex-shrink:0 so its own row
+      // count never affects it), and renumber must be idempotent to avoid a
+      // ResizeObserver feedback loop: only width changes re-trigger it.
       var lh = parseFloat(getComputedStyle(body).lineHeight) || 1;
+      var tops = [];
+      for (var i = 0; i < lines.length; i++) {
+        tops.push(lines[i].getBoundingClientRect().top);
+      }
       gutter.textContent = '';
       var frag = document.createDocumentFragment();
-      for (var i = 0; i < lines.length; i++) {
+      for (var j = 0; j < lines.length; j++) {
+        var span;
+        if (j < lines.length - 1) {
+          span = tops[j + 1] - tops[j];
+        } else {
+          span = lines[j].getBoundingClientRect().height;
+        }
+        var rows = Math.max(1, Math.round(span / lh));
         var num = document.createElement('span');
         num.className = 'gutline';
-        num.textContent = String(i + 1);
+        num.textContent = String(j + 1);
         frag.appendChild(num);
-        var rows = Math.max(1, Math.round(lines[i].getBoundingClientRect().height / lh));
         for (var r = 1; r < rows; r++) {
           var blank = document.createElement('span');
           blank.className = 'gutline';