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CB-WP-0025 T01: survey -- the baseline found the game before the solver did

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CB-RES-0008 with a runnable baseline
(games/ground/examples/difficulty-baseline.rs), and the measurement
produced a finding before any solver exists.

A GREEDY BOT WINS 200 OF 200 GAMES AT FIVE AND SIX SEATS. Median margin
+3, 11.8-12.0 points available against a threshold of 9. The curve is
66% / 82.5% / 95% / 100% / 100% across 2/3/4/5/6 seats.

Row-level, as GROUND-WP-0004 T02 requires: available points 6 / 9 / 12
against thresholds 5 / 7 / 9, so the ratio RISES with seat count (1.20,
1.29, 1.33) while the table also gains actions per round to clear it with.
Three multipliers pointing the same direction.

It also explains the maintainer's report without needing a solver at all:
"I felt it was too easy but then we lost" is two true statements about
different seat counts.

Cost measured and it rules out the obvious approach. Branching is small
(mean 4.7-9.1) but legal_commands costs 112-161 us per call because it
filters candidates through full validate. Exhaustive search is out at
every seat count; 10^4-10^5 nodes is 1.4-14 seconds, which is the budget
the ADR must design inside.

Prior art names the trap: determinized search (PIMC) suffers strategy
fusion (Frank, Basin & Matsubara 1998) -- the search picks different
actions in states a real player cannot distinguish, so the witness may
require knowing what was on top of the deck. Such a line still replays
green, so the checkability benchmark does not catch it. Honesty and
checkability are different properties; stated explicitly so T03 cannot
conflate them.

The survey states its own most likely killer up front (§6): a view-only
search cannot fold events, so making the information boundary structural
rather than a promise may not be affordable. Better found here than in
T05.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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tegwick 2026-08-05 17:52:46 +02:00
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37
workplans/CB-WP-0025-could-we-have-won.md
View file

@ -2,7 +2,7 @@
id: CB-WP-0025
kind: product
title: "Could we have won: a path out of a lost game, and how hard the game actually is"
status: ready
status: active
state_hub_workstream_id: "a866982f-94e7-432b-b0d5-2fefb781a574"
---
@ -90,7 +90,7 @@ whose meaning drifts the next time a bot improves.
```task
id: CB-WP-0025-T01
status: todo
status: done
priority: high
state_hub_task_id: "556cfd24-5992-4cc0-be90-0b60e989b5bb"
```
@ -123,6 +123,39 @@ per dimension — a number or a reproducible comparison, not an impression.
that cannot finish while the player is still looking at the page is a
different feature.
**Done 2026-08-05.**
[CB-RES-0008](../research/CB-RES-0008-could-we-have-won.md), with a
runnable baseline (`games/ground/examples/difficulty-baseline.rs`).
**The baseline produced a finding before any solver exists, and it is the
biggest thing in this pass.** A greedy bot wins **200 of 200** games at
five and six seats — with a median margin of +3 and 11.8–12.0 points
available against a threshold of 9. The curve is 66% / 82.5% / 95% / 100%
/ 100% across 2/3/4/5/6 seats.
The row-level table shows why: available points go **6 / 9 / 12** against
thresholds **5 / 7 / 9**, so the ratio *rises* with seat count (1.20 →
1.29 → 1.33) while the table also gains actions per round. **Three
multipliers pointing the same way.**
**It also explains the maintainer's report without a solver.** *"I felt it
was too easy but then we lost"* — 66% at two seats is a real game; 100% at
six is not. Both halves are true of different seat counts.
**Cost measured, and it rules out the obvious approach.** Branching is
small (mean 4.7–9.1) but `legal_commands` costs **112–161 µs** per call,
because it filters candidates through full `validate`. Exhaustive search
is out at every seat count; ~10⁴–10⁵ nodes is 1.4–14 s, which is the
budget the ADR must design inside.
**Prior art names the trap.** Determinized search (PIMC) suffers *strategy
fusion* — Frank, Basin & Matsubara 1998 — where the search picks different
actions in states a real player cannot tell apart. A witness built that
way may require knowing what was on top of the deck. **And it would still
replay green**, so the checkability benchmark does not catch it. Honesty
and checkability are different properties, stated so T03 cannot conflate
them.
## Task: adversarial review
```task