Robber placement and victim choice

What each arm changes

The search shortlists four robber placements by a static score and lets the lookahead choose among them. The score adds, per hex, the pips blocked at every rival building (cities double, weighted by the blocked seat's public points), and per victim a bonus for hand size and public points. Each arm changes exactly one part of that score, everything else held fixed:

The cohorts

Every cohort seats the arm and the unchanged control v2:{"depth":2} with eta and fast on 64 deterministic seeds played once per rotation (256 games). All games completed; there were no invalid moves, stalls, or interruptions.

Why the slot-0 contrasts are not arm effects

Two identical searches placed in adjacent slots of this arena differ by a seating term that the seating diagnosis traced to turn-order adjacency: the seat directly before another acts first after three of the four rolls in a round. Every cohort above has the changed seat and the control adjacent, so each contrast mixes the arm's effect with the term. Pairing a same-orientation cohort with a swapped cohort on the same seeds cancels it exactly: the bias-free effect is half the per-seed difference of the two contrasts, and half their sum is the seating term itself.

Read against the seating term, the picture is consistent: the dev-seed contrasts of +0.117 to +0.160 were the term plus whatever the seed selection added (the screens that chose these arms ran on seeds 0 to 15, inside the 0-63 cohorts), the fresh-seed contrasts near +0.035 were mostly the term, and the bias-free effects hover slightly below zero. The need arm is the one clear result: its interval excludes zero on the wrong side, so choosing the victim by the card this seat needs is worse than choosing by hand size at this table, plausibly because a big hand is worth more to rob than a well-aimed single card, and the need rule also ignores how many cards the victim holds.

Where the robber actually goes

The arena records every robber placement together with the points leader among the mover's rivals and that seat's highest-pip hex, cities counting double. Pooled over all nine cohorts (2,304 games), the default search landed the robber on that leader's best hex on 27.7 percent of its robber moves and robbed the leader on 45.5 percent. The leader arm raised both shares as designed (28.6 and 49.6 percent), the need arm changed victims rather than hexes, and the threat arm robbed the leader on 46.5 percent while sparing its low-threat partners. The builder policies behind eta and fast block the leader's best hex on about a third of their robber moves, so the default search was the least leader-aware robber at this table, and making it more leader-aware did not win more games.

Failures and limits

The screens on 16 seeds (unregistered, 64 games each) read +0.312, +0.219, and +0.203, all larger than anything that followed: small screens overstate. The development cohorts shared seeds with the screens that selected the arms, so their contrasts carry selection on top of the seating term; the only unbiased numbers here are the swapped pairs on seeds 64 to 127. Everything is engine-arena evidence at one lineup (two searches and the two fixed builders, depth 2, deterministic tapes), and the arms were tested one at a time, so a combined arm remains untested.

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