Cursor paging over filtered eligibility must handle empty continuation pages

Observed 2026-09-08 while implementing ender-inference evaluator call selection (COR-4080 / PR #153). A filtered cohort cursor page can legitimately return zero eligible rows and still provide next_cursor when the bounded source scan was consumed by excluded rows. UI pagination must treat cursor presence—not visible row count—as the continuation signal, preserve cumulative eligible-row offsets separately from page numbers, and keep Next enabled on an empty continuation page. Also, cross-page selection must enforce the downstream exact-ID launch ceiling (500 here); otherwise browsing works but launch deterministically fails. Exact-ID and deterministic-random modes reject cursors, so they need bounded local 10-row presentation while ordinary filters use server cursors.

Provenance: code/API contract review, independent review, automated dashboard/cohort tests, and live staging verification on 2026-09-08. Implementation: https://github.com/e3-solutions/ender-inference/pull/153. Deployment evidence: https://github.com/e3-solutions/ender-inference/actions/runs/34198843020. No call data included.