Replace PDF.js canvas with native browser iframe PDF viewer

- Browser renders PDF exactly as-is using its built-in viewer (Chrome/Edge/Firefox)
- No external dependencies - just a blob URL in an <iframe>
- Page navigation via #page=N fragment syncs PDF view with playback position
- Fixed flex layout so iframe fills remaining height correctly
- Removed PDF.js script tag

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

static/app.js

@@ -21,9 +21,8 @@ const audioCache = new Map();
 let allModels    = {};
 let currentUser  = null;
 
-// PDF.js state
-let pdfDoc       = null;
-const pageCanvases = [];  // canvas elements per page
+// PDF blob URL for native browser viewer
+let pdfBlobUrl = null;
 
 // ── DOM ────────────────────────────────────────────────────────────
 const $  = id => document.getElementById(id);
@@ -184,70 +183,45 @@ function renderText(sentences) {
 // ── VIEW SWITCHING ─────────────────────────────────────────────────
 function setView(mode) {
   state.currentView = mode;
-  const textViewer = $('text-viewer');
-  const pdfViewer  = $('pdf-viewer');
   const contentArea = $('content-area');
-  const btnText = $('btn-view-text');
-  const btnPdf  = $('btn-view-pdf');
 
   if (mode === 'pdf') {
-    textViewer.style.display = 'none';
-    pdfViewer.style.display  = '';
+    $('text-viewer').style.display = 'none';
+    $('pdf-viewer').style.display  = 'flex';
     contentArea.classList.add('pdf-mode');
-    btnPdf.classList.add('active');
-    btnText.classList.remove('active');
+    $('btn-view-pdf').classList.add('active');
+    $('btn-view-text').classList.remove('active');
     $('doc-hint').textContent = 'Viewing original PDF · switch to Text to click sentences';
   } else {
-    textViewer.style.display = '';
-    pdfViewer.style.display  = 'none';
+    $('text-viewer').style.display = '';
+    $('pdf-viewer').style.display  = 'none';
     contentArea.classList.remove('pdf-mode');
-    btnText.classList.add('active');
-    btnPdf.classList.remove('active');
+    $('btn-view-text').classList.add('active');
+    $('btn-view-pdf').classList.remove('active');
     $('doc-hint').textContent = 'Click any sentence to jump there · Space to play/pause · ← → to skip';
   }
 }
 window.setView = setView;
 
-// ── PDF.js RENDERING ───────────────────────────────────────────────
-async function renderPDF(b64) {
-  if (typeof pdfjsLib === 'undefined') return;
-  pdfjsLib.GlobalWorkerOptions.workerSrc =
-    'https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.worker.min.js';
-
-  const pdfPages = $('pdf-pages');
-  pdfPages.innerHTML = '';
-  pageCanvases.length = 0;
+// ── PDF NATIVE RENDERING ───────────────────────────────────────────
+function renderPDF(b64) {
+  // Revoke previous blob to free memory
+  if (pdfBlobUrl) { URL.revokeObjectURL(pdfBlobUrl); pdfBlobUrl = null; }
 
   const binary = atob(b64);
   const bytes  = new Uint8Array(binary.length);
   for (let i = 0; i < binary.length; i++) bytes[i] = binary.charCodeAt(i);
+  const blob = new Blob([bytes], { type: 'application/pdf' });
+  pdfBlobUrl = URL.createObjectURL(blob);
 
-  pdfDoc = await pdfjsLib.getDocument({ data: bytes }).promise;
+  const pdfPages = $('pdf-pages');
+  pdfPages.innerHTML = '';
 
-  for (let i = 1; i <= pdfDoc.numPages; i++) {
-    const page = await pdfDoc.getPage(i);
-    const vp   = page.getViewport({ scale: 1.5 });
-
-    const wrap   = document.createElement('div');
-    wrap.className = 'pdf-page-wrap';
-    wrap.dataset.page = i - 1;
-
-    const canvas = document.createElement('canvas');
-    canvas.width  = vp.width;
-    canvas.height = vp.height;
-    canvas.style.width  = Math.min(vp.width, 800) + 'px';
-    canvas.style.height = (Math.min(vp.width, 800) / vp.width * vp.height) + 'px';
-
-    await page.render({ canvasContext: canvas.getContext('2d'), viewport: vp }).promise;
-    wrap.appendChild(canvas);
-
-    const lbl = document.createElement('div');
-    lbl.className = 'pdf-page-num';
-    lbl.textContent = `Page ${i}`;
-    pdfPages.appendChild(wrap);
-    pdfPages.appendChild(lbl);
-    pageCanvases.push(wrap);
-  }
+  const iframe = document.createElement('iframe');
+  iframe.id  = 'pdf-iframe';
+  iframe.src = pdfBlobUrl;
+  iframe.style.cssText = 'width:100%;height:100%;border:none;display:block;';
+  pdfPages.appendChild(iframe);
 }
 
 function buildSentencePageMap(pageTexts, sentences) {
@@ -269,8 +243,12 @@ function buildSentencePageMap(pageTexts, sentences) {
 }
 
 function scrollPDFToPage(pageIdx) {
-  if (pageIdx < 0 || pageIdx >= pageCanvases.length) return;
-  pageCanvases[pageIdx].scrollIntoView({ behavior: 'smooth', block: 'start' });
+  if (!pdfBlobUrl) return;
+  const iframe = $('pdf-iframe');
+  if (!iframe) return;
+  // #page= fragment navigates inside Chrome/Edge native PDF viewer
+  const target = pdfBlobUrl + '#page=' + (pageIdx + 1);
+  if (iframe.src !== target) iframe.src = target;
 }
 
 // ── LOAD DOCUMENT ──────────────────────────────────────────────────

static/index.html

@@ -219,7 +219,6 @@
   <p id="loading-text">Loading…</p>
 </div>
 
-<script src="https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.min.js"></script>
 <script src="/static/app.js"></script>
 </body>
 </html>

static/style.css

@@ -201,8 +201,12 @@ textarea:focus, .text-field:focus { border-color: var(--accent); }
 .content-area {
   flex: 1; overflow-y: auto; padding: 44px 56px;
   display: flex; flex-direction: column;
+  min-height: 0;
+}
+.content-area.pdf-mode {
+  padding: 20px 20px 0;
+  overflow: hidden;   /* iframe fills remaining height */
 }
-.content-area.pdf-mode { padding: 24px 24px 0; overflow: hidden; }
 .document-header { margin-bottom: 28px; }
 .doc-title-row { display: flex; align-items: flex-start; gap: 12px; margin-bottom: 6px; }
 .document-title { font-size: 22px; font-weight: 700; flex: 1; }
@@ -281,22 +285,25 @@ textarea:focus, .text-field:focus { border-color: var(--accent); }
 
 /* ── PDF VIEWER ──────────────────────────── */
 .pdf-viewer {
-  flex: 1; overflow-y: auto; padding: 24px; background: #1a1a1a;
-  display: flex; flex-direction: column; align-items: center; gap: 16px;
+  flex: 1;
+  min-height: 0;        /* essential: lets flex child shrink below content size */
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
 }
-#pdf-pages { display: flex; flex-direction: column; gap: 16px; align-items: center; width: 100%; }
-.pdf-page-wrap {
-  position: relative; box-shadow: 0 4px 24px rgba(0,0,0,.5);
-  border-radius: 4px; overflow: hidden; max-width: 100%;
+#pdf-pages {
+  flex: 1;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
 }
-.pdf-page-wrap canvas { display: block; max-width: 100%; height: auto; }
-.pdf-page-highlight {
-  position: absolute; border-radius: 2px;
-  background: rgba(124,58,237,.35);
-  pointer-events: none; transition: opacity .2s;
-}
-.pdf-page-num {
-  text-align: center; font-size: 11px; color: var(--text-d); margin-top: 4px;
+#pdf-iframe {
+  flex: 1;
+  min-height: 0;
+  width: 100%;
+  border: none;
+  display: block;
 }
 
 /* ── SETTINGS SIDEBAR ────────────────────── */