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>
Each repository interface now has a contract suite under
src/__contracts__/. Both Mock and Payload implementations run the
same suite, eliminating mock-vs-real drift. Payload impls back the
contract with an in-memory stub via vi.mock('payload') + a small
buildPayloadStub helper.
Spec: §5.2, §6.4