Fix Invalid PDF structure after reload for uploaded documents.

Stop inventing /fixtures/pdfs/<title> URLs when blob bytes are missing;
rely on IndexedDB-hydrated byte store. Seeded tests set an explicit fixture
uri. Session metadata already survived; PDF bytes now survive too.

tests/integration/helpers/seed-session.ts

@@ -49,10 +49,18 @@ export function seedSessionWithDoc(opts: SeedOptions): SeedResult {
     lastOpenedAt: now,
   };
 
+  // Stable HTTP fixture URI so the viewer mounts without IndexedDB bytes.
+  // (resolvePdfViewerUrl no longer invents /fixtures paths from title alone —
+  // that produced "Invalid PDF structure" for arbitrary uploads after reload.)
   const document: Document = {
     id: documentId,
     mediaType: "application/pdf",
-    ...(opts.documentTitle ? { title: opts.documentTitle } : {}),
+    ...(opts.documentTitle
+      ? {
+          title: opts.documentTitle,
+          uri: `/fixtures/pdfs/${encodeURIComponent(opts.documentTitle)}`,
+        }
+      : {}),
     fingerprint: "seed-fingerprint",
     createdAt: now,
     updatedAt: now,