fix(blog): return the exact window for non-aligned offsets

Payload paginates by page, so floor(offset/limit)+1 alone returned the
wrong window whenever offset % limit != 0 (B9). Fetch the straddled
pages and slice the intra-page remainder. The test stub now honours
page like real Payload (it silently ignored it before), and the
contract pins aligned + non-aligned windows on mock and stub alike.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/blog/src/__contracts__/articles-repository.contract.ts

@@ -94,6 +94,46 @@ export const articlesRepositoryContract =
         expect(result[0]?.authorId).toBe("author-a");
       });
 
+      it("getArticles returns the exact window for an aligned offset", async () => {
+        const created = [];
+        for (let i = 0; i < 5; i++) {
+          created.push(await repo.createArticle(articleFactory.build()));
+        }
+        const window = await repo.getArticles({ offset: 2, limit: 2 });
+        expect(window.map((a) => a.id)).toEqual([
+          created[2]?.id,
+          created[3]?.id,
+        ]);
+      });
+
+      it("getArticles returns the exact window for a non-aligned offset", async () => {
+        const created = [];
+        for (let i = 0; i < 5; i++) {
+          created.push(await repo.createArticle(articleFactory.build()));
+        }
+        // offset 3 with limit 2 straddles two limit-sized pages
+        const window = await repo.getArticles({ offset: 3, limit: 2 });
+        expect(window.map((a) => a.id)).toEqual([
+          created[3]?.id,
+          created[4]?.id,
+        ]);
+      });
+
+      it("getArticles non-aligned offset near the end returns only the remaining items", async () => {
+        const created = [];
+        for (let i = 0; i < 5; i++) {
+          created.push(await repo.createArticle(articleFactory.build()));
+        }
+        const window = await repo.getArticles({ offset: 4, limit: 3 });
+        expect(window.map((a) => a.id)).toEqual([created[4]?.id]);
+      });
+
+      it("getArticles offset past the end returns an empty array", async () => {
+        await repo.createArticle(articleFactory.build());
+        const window = await repo.getArticles({ offset: 7, limit: 3 });
+        expect(window).toEqual([]);
+      });
+
       // --- updateArticle ---
 
       it("updateArticle changes fields and returns updated article", async () => {