#260: .swapbtn grid for copy feedback (fix attempt 2)

Label and checkmark stack in one grid cell (inline-grid, grid-area 1/1,
checkmark visibility-hidden until .ok), so the button width is static by
construction across the click. Replaces the min-width pin from fix attempt
1, which enlarged buttons by up to 0.64px (ceil of fractional width) and
leaked the pin after restore.

Applies to paste-view Copy/Link (paste.html + paste.js copyFeedback) and
the /new result-box copy button (new.js). Verified with CDP bounding-box
probes: Copy width/x identical before/during/after at 1400x900 and
375x812 (including the previously failing 52.36px mobile case), Link
button static, checkmark visible during feedback, no minWidth pin set.

internal/web/static/app.css

@@ -580,6 +580,14 @@ a.admin-link:hover { color: var(--fg); text-decoration: underline; }
   outline-offset: 1px;
 }
 
+/* swapbtn (#260): the label and the checkmark occupy the same grid cell, so
+   toggling feedback never changes the button's width — no pinning needed */
+.swapbtn { display: inline-grid; }
+.swapbtn > * { grid-area: 1 / 1; }
+.swapbtn .btn-check { visibility: hidden; }
+.swapbtn.ok .btn-check { visibility: visible; }
+.swapbtn.ok .btn-label { visibility: hidden; }
+
 /* in-place copy success feedback (#53) */
 .iconbtn.ok, .btn.ok {
   color: var(--ok);

internal/web/static/new.js

@@ -192,18 +192,14 @@ async function create() {
 // button, password auto-unlock, then redirect to the paste.
 function finishCreate(data) {
   const url = location.origin + '/' + (data.custom_slug || data.id);
-  showResult('<a href="' + url + '">' + url + '</a> <button class="btn btn-icon" id="result-copy" title="Copy URL" type="button">⧉</button>', 'ok');
+  showResult('<a href="' + url + '">' + url + '</a> <button class="btn btn-icon swapbtn" id="result-copy" title="Copy URL" type="button"><span class="btn-label">⧉</span><span class="btn-check">✓</span></button>', 'ok');
   $('result').dataset.token = data.deletion_token || '';
   const copyBtn = document.getElementById('result-copy');
   copyBtn.addEventListener('click', () => {
     try {
       navigator.clipboard.writeText(url);
       copyBtn.classList.add('ok');               // in-place success feedback (#53)
-      // #260: pin the pre-swap width so the wider/narrower glyph never
-      // shifts neighbouring elements; release it when the label restores.
-      copyBtn.style.minWidth = Math.ceil(copyBtn.getBoundingClientRect().width) + 'px';
-      copyBtn.textContent = '✓';
-      setTimeout(() => { copyBtn.classList.remove('ok'); copyBtn.textContent = '⧉'; copyBtn.style.minWidth = ''; }, 2000);
+      setTimeout(() => copyBtn.classList.remove('ok'), 2000);
     } catch(e) { toast('Copy failed', 'error'); }
   });
   // token carried via sessionStorage, never in the URL (#143)

internal/web/static/paste.js

@@ -18,17 +18,11 @@ function toggleStats() {
 }
 function copyFeedback(btn) {
   if (!btn) return;
-  if (!btn.dataset.label) btn.dataset.label = btn.textContent; // remember the original label (Copy/Link)
-  // #260: keep the button width static during the feedback so surrounding
-  // elements never jump. Pin the pre-swap width, release it on restore.
-  if (!btn.dataset.pinned) {
-    btn.style.minWidth = Math.ceil(btn.getBoundingClientRect().width) + 'px';
-    btn.dataset.pinned = '1';
-  }
+  // #260: the .swapbtn grid stacks label + checkmark in one cell, so the
+  // width is static by construction — feedback is a pure class toggle.
   btn.classList.add('ok');
-  btn.textContent = '✓';
   clearTimeout(btn._okh);
-  btn._okh = setTimeout(() => { btn.classList.remove('ok'); btn.textContent = btn.dataset.label; }, 2000);
+  btn._okh = setTimeout(() => btn.classList.remove('ok'), 2000);
 }
 function copyContent(btn) {
   navigator.clipboard.writeText(document.getElementById('raw-content').value)

internal/web/templates/paste.html

@@ -8,8 +8,8 @@
       <div class="spacer"></div>
       <button type="button" class="iconbtn wrap-toggle" title="Toggle line wrap" aria-pressed="false">Wrap</button>
       <a class="iconbtn" href="/raw/{{.ID}}">Raw</a>
-      <a class="iconbtn" href="#" id="copy-link-btn">Link</a>
-      <a class="iconbtn" href="#" id="copy-btn">Copy</a>
+      <a class="iconbtn swapbtn" href="#" id="copy-link-btn"><span class="btn-label">Link</span><span class="btn-check">✓</span></a>
+      <a class="iconbtn swapbtn" href="#" id="copy-btn"><span class="btn-label">Copy</span><span class="btn-check">✓</span></a>
       {{if .DeletionToken}}<a class="iconbtn danger" href="#" id="delete-btn">Delete</a>{{end}}
     </div>
   </div>