Fix #194: gutter alignment and doubled line spacing in paste viewer

- paste-lines.js: join .codeline spans with no separator; newline text
  nodes between display:block spans in the white-space:pre container each
  rendered as an extra empty line box, doubling visual line spacing and
  desyncing the gutter in both wrap and no-wrap modes
- number only real lines: a paste ending in newline produced a phantom
  trailing number (6 for 5 lines)

internal/web/static/paste-lines.js

@@ -12,8 +12,10 @@
     return document.documentElement.hasAttribute('data-wrap');
   };
 
-  // Wrap each logical line (split on newline; spans never contain newlines
+  // #194: join with NO separator. .codeline is display:block, so a '\n'
-  // because HighlightCode highlights per line) in a .codeline block.
+  // text node between spans is an extra line box in the white-space:pre
+  // container — that doubled the visual line spacing and desynced the
+  // gutter in BOTH modes.
   function splitLines() {
     var html = body.innerHTML;
     var parts = html.split('\n');
@@ -21,13 +23,17 @@
     for (var i = 0; i < parts.length; i++) {
       out.push('<span class="codeline">' + parts[i] + '</span>');
     }
-    body.innerHTML = out.join('\n');
+    body.innerHTML = out.join('');
   }
 
   function renumber() {
     var lines = body.querySelectorAll('.codeline');
+    // #194: a paste ending in '\n' produces one trailing empty .codeline;
+    // number only real lines (like every editor) so the count matches.
+    var count = lines.length;
+    if (count > 1 && lines[count - 1].textContent === '') count--;
     var s = '';
-    if (wrapOn() && lines.length) {
+    if (wrapOn() && count) {
       // 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.
@@ -37,7 +43,7 @@
       var lh = parseFloat(getComputedStyle(body).lineHeight) || 1;
       gutter.textContent = '';
       var frag = document.createDocumentFragment();
-      for (var i = 0; i < lines.length; i++) {
+      for (var i = 0; i < count; i++) {
         var num = document.createElement('span');
         num.className = 'gutline';
         num.textContent = String(i + 1);
@@ -52,8 +58,8 @@
       }
       gutter.appendChild(frag);
     } else {
-      for (var k = 1; k <= lines.length; k++) s += k + '\n';
+      for (var k = 1; k <= count; k++) s += k + '\n';
-      gutter.textContent = lines.length ? s.slice(0, -1) : '1';
+      gutter.textContent = count ? s.slice(0, -1) : '1';
     }
   }