diff --git a/backend/src/modules/note-shares/repository.test.ts b/backend/src/modules/note-shares/repository.test.ts
new file mode 100644
index 0000000..dceac3f
--- /dev/null
+++ b/backend/src/modules/note-shares/repository.test.ts
@@ -0,0 +1,54 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const findManyMock = vi.fn();
+
+vi.mock('../../lib/datastore.js', () => ({
+  getCollection: vi.fn(() => ({
+    findMany: findManyMock,
+  })),
+}));
+
+import { findShareByToken } from './repository.js';
+
+function shareDoc(overrides: { expiresAt?: string } = {}) {
+  return {
+    id: 's1',
+    productId: 'notelett',
+    workspaceId: 'w1',
+    userId: 'u1',
+    noteId: 'n1',
+    shareToken: 'tok',
+    createdAt: new Date().toISOString(),
+    ...overrides,
+  };
+}
+
+describe('findShareByToken', () => {
+  beforeEach(() => {
+    findManyMock.mockReset();
+  });
+
+  it('returns null when expiresAt is in the past', async () => {
+    const past = new Date(Date.now() - 86_400_000).toISOString();
+    findManyMock.mockResolvedValueOnce([shareDoc({ expiresAt: past })]);
+    await expect(findShareByToken('tok', 'notelett')).resolves.toBeNull();
+  });
+
+  it('returns share when expiresAt is in the future', async () => {
+    const future = new Date(Date.now() + 86_400_000).toISOString();
+    const doc = shareDoc({ expiresAt: future });
+    findManyMock.mockResolvedValueOnce([doc]);
+    await expect(findShareByToken('tok', 'notelett')).resolves.toEqual(doc);
+  });
+
+  it('returns share when expiresAt is absent', async () => {
+    const doc = shareDoc();
+    findManyMock.mockResolvedValueOnce([doc]);
+    await expect(findShareByToken('tok', 'notelett')).resolves.toEqual(doc);
+  });
+
+  it('returns null when no row matches', async () => {
+    findManyMock.mockResolvedValueOnce([]);
+    await expect(findShareByToken('tok', 'notelett')).resolves.toBeNull();
+  });
+});
diff --git a/backend/src/modules/note-shares/repository.ts b/backend/src/modules/note-shares/repository.ts
index 69aba65..56597de 100644
--- a/backend/src/modules/note-shares/repository.ts
+++ b/backend/src/modules/note-shares/repository.ts
@@ -16,7 +16,15 @@ export async function findShareByToken(
 ): Promise<NoteShareDoc | null> {
   const filter: FilterMap = { shareToken, productId };
   const items = await collection().findMany({ filter, limit: 1 });
-  return items[0] ?? null;
+  const share = items[0] ?? null;
+  if (!share) return null;
+  if (share.expiresAt) {
+    const exp = Date.parse(share.expiresAt);
+    if (!Number.isNaN(exp) && exp < Date.now()) {
+      return null;
+    }
+  }
+  return share;
 }
 
 export async function listSharesForNote(