fix(preview): exclude the panel from tab order while closed (real Shift+Tab root cause)

index.html

@@ -123,13 +123,13 @@ <h2 id="empty-title"></h2>
         <div class="file-preview-panel" id="file-preview-modal">
           <div class="file-preview-head">
             <span class="file-preview-title" id="file-preview-title"></span>
-            <button class="btn" id="file-preview-copy" data-i18n-title="copy">
+            <button class="btn" id="file-preview-copy" data-i18n-title="copy" tabindex="-1">
               <svg viewBox="0 0 24 24" width="14" height="14"><path fill="currentColor" d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg>
             </button>
-            <button class="btn" id="file-preview-edit" data-i18n-title="edit">
+            <button class="btn" id="file-preview-edit" data-i18n-title="edit" tabindex="-1">
               <svg viewBox="0 0 24 24" width="14" height="14"><path fill="currentColor" d="M3 17.25V21h3.75L17.81 9.94l-3.75-3.75L3 17.25zM20.71 7.04a1 1 0 0 0 0-1.41l-2.34-2.34a1 1 0 0 0-1.41 0l-1.83 1.83 3.75 3.75 1.83-1.83z"/></svg>
             </button>
-            <button class="btn" id="file-preview-close" data-i18n-title="close">
+            <button class="btn" id="file-preview-close" data-i18n-title="close" tabindex="-1">
               <svg viewBox="0 0 24 24" width="14" height="14"><path fill="currentColor" d="m6.4 5 5.6 5.6L17.6 5 19 6.4 13.4 12l5.6 5.6-1.4 1.4-5.6-5.6L6.4 19 5 17.6 10.6 12 5 6.4z"/></svg>
             </button>
           </div>

src/main.ts

@@ -3428,6 +3428,23 @@ function showLinkToast(text: string) {
 const filePreviewModal = $("#file-preview-modal");
 const filePreviewTitle = $("#file-preview-title");
 const filePreviewBody = $("#file-preview-body");
+// The panel stays in the DOM (translated off-screen) rather than
+// display:none, so its CSS slide transition can animate — but that also
+// keeps its buttons in the page's normal tab order while "closed". xterm.js
+// deliberately leaves Shift+Tab uncancelled (so app-level Shift+Tab chords
+// like Claude Code's plan-mode toggle still reach the pty), which means the
+// browser's native reverse-tab-order focus navigation runs — and can land
+// right here, scrolling the off-screen panel into view. tabindex="-1" while
+// closed removes it from that path entirely; restored while open so the
+// panel itself is still keyboard-navigable.
+const filePreviewFocusables = [
+  $("#file-preview-copy"),
+  $("#file-preview-edit"),
+  $("#file-preview-close"),
+];
+function setFilePreviewFocusable(focusable: boolean) {
+  for (const el of filePreviewFocusables) el.tabIndex = focusable ? 0 : -1;
+}
 
 // Tracks the live Three.js scene/renderer for the currently open model
 // preview (if any) so it can be torn down before the next preview replaces
@@ -3440,6 +3457,7 @@ function disposeModelPreview() {
 
 function closeFilePreview() {
   filePreviewModal.classList.remove("open");
+  setFilePreviewFocusable(false);
   disposeModelPreview();
   setPreviewEditing(false);
   // Release state immediately rather than leaving the last-viewed file
@@ -3569,6 +3587,7 @@ async function openFilePreview(raw: string, cwd: string | null) {
   filePreviewBody.className = "file-preview-body plain";
   filePreviewBody.textContent = "…";
   filePreviewModal.classList.add("open");
+  setFilePreviewFocusable(true);
   // Move focus off the terminal and onto the panel: xterm's own keydown
   // handler treats Escape as a key it must own (cancels the browser event
   // unconditionally), which stops it from ever reaching our document-level