fix(page): resolve Contents ref before appending content streams

When a page's /Contents is a reference to an array (not a single stream),
the append/prepend methods need to expand the array items into the new
contents array. Previously, the indirect reference to the array was kept,
causing PDF viewers to fail rendering the original page content.

Author: Mythie

src/api/pdf-page.ts

@@ -2200,8 +2200,27 @@ export class PDFPage {
     }
 
     if (existingContents instanceof PdfRef) {
-      // Reference to a stream - wrap in array with our content first
-      this.dict.set("Contents", new PdfArray([newContent, existingContents]));
+      // Resolve the reference to check if it's an array or a stream
+      const resolved = this.ctx.resolve(existingContents);
+
+      if (resolved instanceof PdfArray) {
+        // Reference points to an array of streams - prepend our stream to a new array
+        // containing all items from the resolved array
+        const newArray = new PdfArray([newContent]);
+
+        for (let i = 0; i < resolved.length; i++) {
+          const item = resolved.at(i);
+
+          if (item) {
+            newArray.push(item);
+          }
+        }
+
+        this.dict.set("Contents", newArray);
+      } else {
+        // Reference points to a single stream - wrap in array with our content first
+        this.dict.set("Contents", new PdfArray([newContent, existingContents]));
+      }
 
       // Mark as modified to prevent double-wrapping in appendContent
       this._contentWrapped = true;
@@ -2260,7 +2279,29 @@ export class PDFPage {
       const QStream = this.createContentStream("\nQ");
 
       if (existingContents instanceof PdfRef) {
-        this.dict.set("Contents", new PdfArray([qStream, existingContents, QStream, newContent]));
+        // Resolve the reference to check if it's an array or a stream
+        const resolved = this.ctx.resolve(existingContents);
+
+        if (resolved instanceof PdfArray) {
+          // Reference points to an array of streams - expand it
+          const newArray = new PdfArray([qStream]);
+
+          for (let i = 0; i < resolved.length; i++) {
+            const item = resolved.at(i);
+
+            if (item) {
+              newArray.push(item);
+            }
+          }
+
+          newArray.push(QStream);
+          newArray.push(newContent);
+
+          this.dict.set("Contents", newArray);
+        } else {
+          // Reference points to a single stream
+          this.dict.set("Contents", new PdfArray([qStream, existingContents, QStream, newContent]));
+        }
 
         return;
       }