clay-borg/workplans/CB-WP-0025-could-we-have-won.md

id	kind	title	status	state_hub_workstream_id
CB-WP-0025	product	Could we have won: a path out of a lost game, and how hard the game actually is	active	a866982f-94e7-432b-b0d5-2fefb781a574

Purpose

structural tier  L   (creates a new capability — a search over game state,
                      and a measurement the engine does not currently take;
                      both produce numbers ground-game will tune against)
chaos            d8 = 6  → no override
declared tier    L

Declaration 8 of chaos window 2. Tier L: separate survey, adversarial review, ADR, then spec, then code.

Two remarks, and why they are one pass

"I had a game where we lost and in this case I would have liked to know if and how we could have won… the best path is not computable I guess so a path to win is fine."

"Do we have difficulty estimations? If so we should show them. It will help tuning the game. I felt it was too easy but then we lost, so who knows."

They are the same machine asked two questions. Was this game winnable? is a search from a recorded state. How hard is this game? is that search run over many deals and counted. Building the second without the first gives a win-rate with no witness; building the first without the second gives one anecdote per game.

"I felt it was too easy but then we lost, so who knows" is the finding. The maintainer cannot calibrate the game from play, and that is precisely the gap ground-game is currently blocked in: GROUND-WP-0005 (Difficulty tiers (threshold ratio) and optional Pressure dial) is active with both its tasks in wait. Tiers cannot be set without a measured baseline, and clay-borg is the thing that can measure. This pass is what unblocks it — which is the design-instrument aspect CB-WP-0022 is in the middle of stating, arriving with a concrete demand.

What already exists, so the survey does not re-find it

• The state is replayable. cb-game-runtime records sessions as scenarios; replay.rs and make replay-test already re-run them. A search does not need new persistence.
• The move space is enumerable. legal_commands exists and, since CB-WP-0023, is narrow enough to be worth trusting — SOLVE is offered only where it can act, so the branching factor is real rather than inflated by inert moves.
• Bots exist. games/ground/src/bot.rs has GreedyPolicy and RandomPolicy, wired through bot_policy (table.rs:208). A win rate over N seeds is reachable with what is already there — the question is whether that number means anything, which is the survey's problem.
• The threshold is public. OutcomeView.total / .threshold / .group_success. Difficulty has a denominator already.

What makes this hard, and must not be waved through

The game is not perfect-information and the search must respect that. A path computed with the deck known is a path the players could never have found. view.rs hides the deck, other seats' hands, and face-down selections by rule (GR-S02/S04, GR-R02/R04). A retrospective solver running on GroundState sees all of it. So the ADR must decide, in words, which of these three the tool answers:

• was this deal winnable by an omniscient player — cheap, honest, and answers a question nobody asked;
• was it winnable from what the seats could see — the question actually asked, and the expensive one;
• did a reasonable line exist — a bounded search from the losing seat's information, which may be the only affordable honest answer.

Getting this wrong produces a feature that tells the maintainer he could have won by playing a card he had no way to know was there. That is worse than not shipping it.

And a difficulty number is a claim about a distribution. One win rate over one bot policy over N seeds is not "the difficulty"; it is that policy's win rate. Whatever the spec adopts must name its policy, its N, and its seed range, or ground-game will tune tiers against a number whose meaning drifts the next time a bot improves.

Task: survey

id: CB-WP-0025-T01
status: done
priority: high
state_hub_task_id: "556cfd24-5992-4cc0-be90-0b60e989b5bb"

research/CB-RES-0008-*.md, with tier: L and the chaos roll recorded (loop-lint checks both).

Per §Step 1 the survey is done when it can name a benchmark-to-beat per dimension — a number or a reproducible comparison, not an impression.

• Retrospective solvers in games with hidden information. The prior art is real and should be named: determinized search (perfect-information Monte Carlo) and its known failure — strategy fusion, where a determinizing solver claims lines that require knowing which world it is in. That failure is exactly the trap in §What makes this hard. Bridge and Skat post-mortem tools are the closest analogues; poker solvers are the well-studied case and the wrong shape.
• "A path to win" as a product, not a proof. The maintainer already conceded optimality ("the best path is not computable I guess"). So the target is a witness: one concrete line of play that reaches group_success, or a defensible no line found within bound B. Name what a witness must carry to be checkable.
• Difficulty as a measured quantity in co-operative games. Pandemic and its relatives set difficulty by a dial with a published win rate. The benchmark-to-beat is: can we produce a win rate whose confidence interval is tight enough to distinguish two threshold settings?
• Cost. Search over an event-sourced aggregate with full validate on every branch has a per-node price. Measure it on our machine, on our scenarios — the runnable-baseline option applies here, since a search that cannot finish while the player is still looking at the page is a different feature.

Done 2026-08-05. CB-RES-0008, with a runnable baseline (games/ground/examples/difficulty-baseline.rs).

Everything this record originally claimed was withdrawn by T02 the same day. Kept as a pointer rather than rewritten, because a claim retracted silently is how three earlier wrong premises survived (ADR-0012 D5).

Claimed: a greedy bot wins 200/200 at five and six seats, so the game is too easy there; the points-to-threshold ratio rises with seat count and explains the curve; legal_commands costs 112–161 µs, so exhaustive search is out; and all of this explains the maintainer's report.

Withdrawn: the win rate is GreedyPolicy's, not the game's (C4 — FirstLegal scores 0% on the same deals); the ratio is identical at 3p and 4p, which differ by 12.5 points (C2); the cost figure was wrong by 30–50× and exhaustive search is affordable (C1, C6); and the maintainer's losses were 3-player games on the pre-ruling deal (C5).

What survives: the harness exists and runs, the 6/9/12 arithmetic is right against Problems.csv, and the branching widths (4.7–9.1) hold. See CB-RES-0008 for the corrected text and the response for the full accounting.

Prior art named the trap — determinized search suffers strategy fusion (Frank, Basin & Matsubara 1998) — and T03 then established it does not apply here. After the game there is one world, so a line found in it is executable in it. Fusion is an obstacle to a playing engine, which this is not.

Task: adversarial review

id: CB-WP-0025-T02
status: done
priority: high
state_hub_task_id: "bdd9fc97-4706-4d8e-b286-91ff53339680"

Tier L requires it. Exactly one round: challenge, then response, trail in history/, unpolished. Require an attempt at:

• that the honest version is unaffordable — that a search respecting the information rule is too expensive or too weak to find anything, so the shipped tool will quietly become the omniscient one with a reassuring label;
• that a witness misleads more than it helps — being shown a line that needed a card you could not know about teaches a wrong lesson about the game, and the tool would be better refusing to answer;
• that the difficulty number is a bot benchmark wearing a difficulty costume, and ground-game will tune the game against our bot rather than against play;
• that this is CB-WP-0022's job — the design instrument is being built right now, and a difficulty measurement is a finding-producing tool. The strongest counter is that the register records findings and this produces them, but the reviewer should press whether that is a distinction worth a separate capability.

Done 2026-08-05. Trail: challenge, response. Separate agent, as in CB-WP-0022.

Six of seven conceded. The survey's headline finding is WITHDRAWN.

C4 kills it and the reviewer ranked it fourth. A FirstLegal policy — legal[0], no heuristic — scores 0% at five and six seats where greedy scores 100%, and 77.5% at two where greedy scores 66%. Two unsophisticated agents span the whole range, so "too easy at 5–6 seats" was about GreedyPolicy, not GROUND.

C1: the node cost was wrong by 30–50× — the timer bracketed whole games — and the tell was in my own output, falling as branching rose. C6: exhaustive search is not out, which changes T03's premise. C3: the finding failed the admissibility rule this project wrote nine hours earlier. C2: 3p and 4p share deal, threshold and ratio and differ by 12.5 points. C5: lib.rs:2487 contradicts the "explains the maintainer" claim — his losses were 3-player on the pre-ruling deal, unwinnable at 6 against 7.

T06 was pointed at GROUND-WP-0005, which is blocked on this number. Sending it would have been the fifth wrong premise to reach ground-game. Both tier-L reviews here have now caught a false headline that every gate passed.

Task: decide

id: CB-WP-0025-T03
status: done
priority: high
state_hub_task_id: "055630a1-56e0-4ad4-8796-35f444313371"

decisions/ADR-0013-*.md. (ADR-0012 is CB-WP-0022 T03's.) At minimum:

• which question the solver answers, from the three in §What makes this hard, and what it is called in the UI — the name must not overclaim;
• the information boundary: whether the search runs on GroundState or on a GroundView, and if on state, what stops it using what the view hides. Note that running on the view makes the rule structural rather than a promise, and that this is the cheapest guarantee available;
• the bound: depth, node budget, or wall clock, and what no path found means against it — a bounded search that says "unwinnable" is lying, and the wording must say "none found within B";
• whether difficulty ships as one number or a small table, and what it is a function of: policy, seat count, threshold, seed range;
• where it lives — a new crate, a mode of cb-play, or a tool under tools/. The tier was declared L on the assumption of a new capability; if the ADR concludes it is a mode of an existing one, say so, and the over-declaration is a chaos-window data point worth recording.

Done 2026-08-05. ADR-0013, seven decisions. Two of them are not what T03 was written expecting, because the review moved the ground under both.

• D1 — strategy fusion does not apply, and that is why this is affordable. Fusion is a defect of aggregating over determinizations to choose a move. After the game there is one world: the deal is known, so a search over it produces a line executable in the only world there is. The survey treated fusion as this pass's central obstacle; it is an obstacle to a playing engine, which we are not building.
• D4 — difficulty is the WINNABLE FRACTION, not any bot's win rate. C4 killed the bot rate: two trivial policies span 0–100% on the same deals, and improving the bot would make the game "easier" without a rule changing. The solver supplies a policy-independent measure — over N deals, in what proportion does a winning line exist — which is a property of the deal distribution and the threshold, and is what GROUND-WP-0005 actually needs. The bot rate never was.

D2 searches GroundState — the survey's view-only boundary is not implementable, since a view cannot fold events — and moves the guarantee to a checkable per-move visible/hidden marking from project(). D3 bounded exhaustive over the last K rounds, with "no winning line found in the last K rounds" normative, never "unwinnable". D5 makes the harness an instrument before any figure is quoted (C3). D6 no new crate and no port — the L declaration was an over-declaration, recorded as one. D7 the node cost is disputed 5×; T04 benchmarks it and neither existing figure may be cited.

Task: specify

id: CB-WP-0025-T04
status: done
priority: high
state_hub_task_id: "7c3ca25d-0001-44ef-a07d-0ab2d51b09a5"

specs/ — extend MetricsAndScenarios.md or add a capability spec as the ADR directs, with metrics, because a spec without them is prose.

Candidates, to be argued not adopted:

• witness checkability — every path the tool emits replays through the existing scenario runner and ends in group_success. Target 100%, and it is a hard gate, not a metric: a path that does not replay is a bug that says the opposite of the truth;
• search cost — nodes and wall clock at the chosen bound, on the recorded games we have;
• difficulty resolution — the smallest threshold difference the measurement can distinguish, with its N. This is the number ground-game needs, and stating it as "we can tell 5 from 7 but not 7 from 8" is more useful than a win rate with no error bar.

Per ground-game's ruling (GROUND-WP-0004 T02), any arithmetic finding this produces ships a runnable reproduction and a row-level table — never a summed figure. A difficulty number is arithmetic, and it is exactly the kind that has already gone wrong twice.

Done 2026-08-05. specs/RetrospectiveAnalysis.md v1.0, and games/ground/benches/search.rs for D7's disputed number.

The benchmark's own first fixture was defective — the same defect class, one layer down. A fixed stop at step 20 put 2p and 4p where seat 0 had no legal commands, so it timed an empty Vec (~120 ns) and silently skipped validate_fold. It now advances to a real branch and asserts it.

Measured at real decision points (table in RetrospectiveAnalysis §3.1): legal_commands 4.06–4.76 µs, clone 378–639 ns, validate+fold 0.5–3.8 µs.

clone is in there because a search must copy state per branch, and iter_batched excludes setup from timing — leaving the budget resting on an unmeasured span, which is precisely C1's mistake. Per-child cost is not uniform: validate+fold ranges 0.5–3.8 µs by command, so budgets use the upper end (~5 µs/child).

That settles D3's affordability with real numbers: joint branching over the last two rounds is ~5×10² / 1.6×10⁵ / 5.7×10⁵ at 2/3/4 seats → negligible / 0.8 s / 2.9 s. K = 2 holds at two to four seats and does not at five or six, where the tool must reduce K and say so rather than silently search less.

§4.1 is a normative prohibition, not a preference: a single-policy win rate may not be reported as a difficulty. The spec carries the measured reason — greedy 100% vs first-legal 0% on identical deals.

Task: build the witness

id: CB-WP-0025-T05
status: todo
priority: high
state_hub_task_id: "5f1cbda3-7427-4f23-8c67-b2e216b987a8"

The search, the bound, and the replayable path. Wire it to the ending page so a lost game can be asked the question — the page CB-WP-0024 T01 is already reworking, so land that first or expect a conflict.

A game that was won is not asked the question. The feature exists for a loss.

Controls:

• every emitted witness replays to group_success through the existing runner — asserted, not spot-checked;
• a deal constructed to be unwinnable returns none found, and the test says which construction makes it so;
• the information boundary is mutation-provable: relax it, and a test naming that boundary goes red. If it cannot be mutated, it was a comment rather than a rule.

Task: measure the difficulty, and hand it to ground-game

id: CB-WP-0025-T06
status: todo
priority: high
state_hub_task_id: "723feae8-1ed4-4dd4-9330-8ec84625e5d9"

Run the measurement, ship it as a make target beside the other instruments, and show the result in the game — the maintainer asked for it to be visible, and a number in a file will not calibrate anything.

Then send it to ground-game against GROUND-WP-0005, which is active with both tasks waiting on exactly this. Per CB-WP-0022 T06, it lands as a file in their repo under their workplan, not only an inbox entry — the message that sat unread for four days is the baseline to beat.

Controls:

• the number regenerates from a single command, and facts.toml carries it if anything else quotes it (§Single source of fact — make facts-check);
• the report carries the row-level table the ruling requires;
• the seed range and policy are in the number's name, not in a footnote.

Task: evidence

id: CB-WP-0025-T07
status: todo
priority: high
state_hub_task_id: "2616e06c-5d88-4680-be18-4452515dff21"

evidence/CB-EV-0023-*.md.

• Was the game winnable, for the maintainer's actual lost game. That is the acceptance test with a face on it.
• What the honest search cost against the omniscient one, since the review will have pressed hardest there.
• Whether the difficulty measurement moved ground-game, or sat.
• What tier L cost against what it caught — third full-weight L pass in the project, and the second in this chaos window.
• Quote CB-WP-0024's cost by re-running the instrument.