fix: address CodeRabbit review feedback

- Handle Headers instance in TSA request detection (not just plain objects)
- Wrap timestampPdf with createCorsAwareFetch for OCSP/cert chain requests
- Pass 'success' type to showAlert on successful timestamp
- Add TSA URL context to timestamp error messages with cause
- Remove redundant Uint8Array wrapping in TimestampNode

src/js/logic/digital-sign-pdf.ts

@@ -208,10 +208,12 @@ function createCorsAwareFetch(): {
 
       const isTsaRequest =
         (init?.headers &&
-          typeof init.headers === 'object' &&
-          'Content-Type' in init.headers &&
-          (init.headers as Record<string, string>)['Content-Type'] ===
-            'application/timestamp-query') ||
+          (init.headers instanceof Headers
+            ? init.headers.get('Content-Type') === 'application/timestamp-query'
+            : typeof init.headers === 'object' &&
+              !Array.isArray(init.headers) &&
+              (init.headers as Record<string, string>)['Content-Type'] ===
+                'application/timestamp-query')) ||
         url.includes('timestamp') ||
         url.includes('/tsa') ||
         url.includes('/tsr') ||
@@ -350,8 +352,14 @@ export async function timestampPdf(
 
   const signer = new PdfSigner(signOptions);
 
-  const timestampedPdfBytes = await signer.sign(pdfBytes);
-  return new Uint8Array(timestampedPdfBytes);
+  const { restore } = createCorsAwareFetch();
+
+  try {
+    const timestampedPdfBytes = await signer.sign(pdfBytes);
+    return new Uint8Array(timestampedPdfBytes);
+  } finally {
+    restore();
+  }
 }
 
 export function getCertificateInfo(certificate: forge.pki.Certificate): {

src/js/logic/timestamp-pdf-page.ts

@@ -238,7 +238,8 @@ async function processTimestamp(): Promise<void> {
 
     showAlert(
       'Success',
-      'PDF timestamped successfully! The timestamp can be verified in Adobe Acrobat and other PDF readers.'
+      'PDF timestamped successfully! The timestamp can be verified in Adobe Acrobat and other PDF readers.',
+      'success'
     );
 
     resetState();

src/js/workflow/nodes/timestamp-node.ts

@@ -43,9 +43,15 @@ export class TimestampNode extends BaseWorkflowNode {
 
     return {
       pdf: await processBatch(pdfInputs, async (input) => {
-        const timestampedBytes = await timestampPdf(input.bytes, tsaUrl);
-
-        const bytes = new Uint8Array(timestampedBytes);
+        let bytes: Uint8Array;
+        try {
+          bytes = await timestampPdf(input.bytes, tsaUrl);
+        } catch (err) {
+          throw new Error(
+            `Failed to timestamp using TSA ${tsaUrl}: ${err instanceof Error ? err.message : err}`,
+            { cause: err }
+          );
+        }
         const document = await PDFDocument.load(bytes);
 
         return {