Test pagination at its boundaries

Inputs: [PAGINATION CONTRACT], [SAMPLE RESPONSES], [SORT KEY]. Examine empty page, final page, concurrent insert and duplicate-sort-key cases. Specify stable ordering and cursor semantics. Output: An edge-case matrix and local test sketches. Check: Concatenating pages gives each expected record once under the stated consistency model. If essential information is missing, identify it rather than filling the gap with a guess. Define the consistency model explicitly before asserting that page concatenation is duplicate-free.