Fix debug NameError: add preview_image_from_pdf and first-page rasterizer helpers

app.py

@@ -558,6 +558,53 @@ def _pdf_to_iframe_file(pdf_path: Path, width="100%", height="900px") -> str:
     except Exception:
         return ""
 
+def _pdf_to_image_first_page(pdf_path: Path, out_dir: Path, logs) -> Path | None:
+    try:
+        out_dir.mkdir(parents=True, exist_ok=True)
+        out_path = out_dir / "poster_preview.png"
+        # Try PyMuPDF
+        try:
+            import fitz  # PyMuPDF
+            doc = fitz.open(str(pdf_path))
+            if doc.page_count == 0:
+                return None
+            page = doc.load_page(0)
+            mat = fitz.Matrix(2, 2)
+            pix = page.get_pixmap(matrix=mat, alpha=False)
+            pix.save(str(out_path))
+            return out_path if out_path.exists() else None
+        except Exception as e:
+            logs.append(f"⚠️ PyMuPDF render failed: {e}")
+        # Fallback: pypdfium2
+        try:
+            import pypdfium2 as pdfium
+            pdf = pdfium.PdfDocument(str(pdf_path))
+            if len(pdf) == 0:
+                return None
+            page = pdf[0]
+            bitmap = page.render(scale=2).to_pil()
+            bitmap.save(out_path)
+            return out_path if out_path.exists() else None
+        except Exception as e:
+            logs.append(f"⚠️ pypdfium2 render failed: {e}")
+    except Exception as e:
+        logs.append(f"⚠️ image preview failed: {e}")
+    return None
+
+def preview_image_from_pdf(pdf_file):
+    try:
+        path = pdf_file
+        if hasattr(pdf_file, 'name'):
+            path = pdf_file.name
+        if not path:
+            return None
+        p = Path(path)
+        logs = []
+        img = _pdf_to_image_first_page(p, p.parent, logs)
+        return str(img) if img and img.exists() else None
+    except Exception:
+        return None
+
 def _compile_tex_to_pdf(tex_path: Path, logs):
     """Generic TeX compile helper for a .tex file. Returns Path to PDF or None."""
     try: