feat(preview): improve failure recovery and configuration

Update the client-side preview status logic to gracefully handle failed
states and return fallback URLs. Add PDF worker tracing to the build
configuration for preview-related API endpoints and include server-side
error logging.

next.config.ts

@@ -17,6 +17,15 @@ const nextConfig: NextConfig = {
     '/api/whisper': [
       './node_modules/ffmpeg-static/ffmpeg',
     ],
+    '/api/documents/blob/preview/ensure': [
+      './node_modules/pdfjs-dist/legacy/build/pdf.worker.mjs',
+    ],
+    '/api/documents/blob/preview/presign': [
+      './node_modules/pdfjs-dist/legacy/build/pdf.worker.mjs',
+    ],
+    '/api/documents/blob/preview/fallback': [
+      './node_modules/pdfjs-dist/legacy/build/pdf.worker.mjs',
+    ],
   },
 };
 

src/lib/client-documents.ts

@@ -328,10 +328,24 @@ export async function getDocumentPreviewStatus(
     };
   }
 
+  // Handle failed preview generation (500 with status: 'failed')
   const contentType = res.headers.get('content-type') || '';
   if (contentType.includes('application/json')) {
-    const data = (await res.json().catch(() => null)) as { error?: string } | null;
-    throw new Error(data?.error || `Failed to load preview status (status ${res.status})`);
+    const data = (await res.json().catch(() => null)) as {
+      status?: string;
+      lastError?: string;
+      error?: string;
+    } | null;
+    if (data?.status === 'failed') {
+      return {
+        kind: 'pending',
+        status: 'failed',
+        retryAfterMs: 0,
+        fallbackUrl: documentPreviewFallbackUrl(id),
+        presignUrl: documentPreviewPresignUrl(id),
+      };
+    }
+    throw new Error(data?.error || data?.lastError || `Failed to load preview status (status ${res.status})`);
   }
 
   throw new Error(`Failed to load preview status (status ${res.status})`);

src/lib/server/document-previews.ts

@@ -388,6 +388,7 @@ export async function ensureDocumentPreview(doc: PreviewSourceDocument, namespac
         eTag: head.eTag,
       });
     } catch (error) {
+      console.error(`[document-previews] Preview generation failed for ${doc.id} (type=${doc.type}):`, error);
       await markPreviewFailed(doc.id, namespaceKey, error);
     }
   }