fix(pdf-server): isEditing on page.render so stamps always divert to annotationCanvasMap

StampAnnotation.hasOwnCanvas defaults to noRotate; stamps without that
flag composited onto the main canvas, so deleting the 'imported' overlay
left an unclickable pixel. isEditing forces hasOwnCanvas=true for stamps
(via mustBeViewedWhenEditing) so the appearance lands in the per-id
canvas and our DOM element is the only render.

Author: ochafik

examples/pdf-server/src/mcp-app.ts

@@ -3246,6 +3246,13 @@ async function renderPage() {
       canvasContext: ctx,
       viewport,
       annotationCanvasMap,
+      // isEditing forces hasOwnCanvas=true for stamps regardless of /F
+      // NoRotate (StampAnnotation.mustBeViewedWhenEditing in pdf.worker).
+      // Without this, stamps without NoRotate composite onto the main canvas
+      // and deleting the "imported" overlay leaves an unclickable pixel
+      // behind. Other markup types still gate on noRotate; for those the
+      // overlay stays a transparent click-box (delete is UI-only until save).
+      isEditing: true,
     });
     currentRenderTask = renderTask;