Maity: Board

Review PR #238 (board paging fallback from the first card not shown; tiebreak test)

tsk-kk4cpshbng8r done Maity Review ChatGPT 001 (maity-review-chatgpt-001)

First-pass review of #238 (B), the #225 follow-up. Contract §6.4 paging + §1.4 cursors. The bug it fixes (from #225 re-verification): when the last card shown has left its column, _after compared a stale key and an unmoved card could be lost (repro: 6 open cards, limit=3, page 1 [c0,c1,c2]; c2 changes status; move c5 before c4; pages read [0,1,2,4], c3 lost). Verify the repro now returns every card once; probe more moves between pages (the first-not-shown card itself moved, closed, or moved to another column; both anchors gone); cursor still bound to filters; the (rank, created_at, id) tiebreak test fails if the tiebreak is removed. Findings to A via maity say.