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Allocate best-placed teams to avoid same-group knockout rematches - #53
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Phase 4 of World Cup style advancement. Best-placed (third-placed) slots were resolved purely by rank, which could — and on the 2026 bracket did — draw a third-placed team against a winner from its own group. FIFA/UEFA solve this with a per-combination allocation table; this finds an equivalent rematch-free assignment directly. - BestPlacedAllocator: backtracking bipartite match assigning the top-N thirds to the N best-placed slots so none faces its own group, tried in rank order over bracket order for a deterministic result. Flags an unavoidable rematch rather than failing. - SeedStageFromGroups resolves best-placed slots as a pool through the allocator (opponent group taken from each slot's round-1 partner); group slots unchanged. Slot payload gains origin_group + rematch. - Seeding review card shows each pooled third's origin group and warns on any unavoidable rematch. Deferred (documented follow-up): manual per-slot swap on the review screen, and draw-mode pairing for UCL-style competitions. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Summary
Phase ④ (final phase) of World Cup–style advancement. Best-placed (third-placed) knockout slots were resolved purely by rank, which could draw a third against a winner from its own group — a rematch. On the real 2026 dev bracket it produced exactly that. FIFA/UEFA avoid it with a published allocation table per group combination; this finds an equivalent rematch-free assignment directly instead of hardcoding those tables.
BestPlacedAllocator— a backtracking bipartite match assigning the top-N qualifying thirds to the N best-placed slots so none faces its own group. Teams tried in ranking order over bracket order → deterministic, keeps stronger thirds earlier. Any combination that admits a rematch-free layout resolves (covers the classic 6-group/4-third table, the 2026 12-group/8-third shape, and everything between). An unavoidable rematch is flagged, not fatal.SeedStageFromGroupsnow resolves best-placed slots as a pool through the allocator (each slot's opponent group taken from its round-1 partner descriptor); group slots resolve exactly as before. Slot payload gainsorigin_groupandrematch.Verified read-only on the real World Cup R32: 0 rematches, all 8 thirds allocated away from their own groups (the allocator reshuffled the seeded-template thirds to achieve it). The updated Phase ③ scaffold previously produced an Alpha One v Alpha Two same-group rematch — now Alpha One v Beta Two.
Completes the plan. Deferred as a documented follow-up: manual per-slot swap on the review screen, and UCL-style
drawpairing mode (qualifiers known, pairings drawn by hand).Testing
BestPlacedAllocatorunit tests: no-own-group guarantee, rank-order preference when unconstrained, full 4-team combination, null-opponent handling, unavoidable-rematch flag, determinism🤖 Generated with Claude Code