clay-borg/evidence/CB-EV-0001-game-kernel.md

# CB-EV-0001 — GROUND game kernel: acceptance evidence

Status: **T08 complete. AM-4 remediated and re-measured 2026-07-31.**
Recorded: 2026-07-31. Amended 2026-07-31 — §4 gains measured savings per
remediation option, and §5 corrects AM-12 from "uncomputable" to
measured-at-session-level; see CB-WP-0002.
Workplan: CB-WP-0001, task T08
Spec: `specs/GameKernel.md` §4 (AM-1..AM-12)
Baseline: `research/CB-RES-0001-game-kernel.md`, measurements in
`research/CB-RES-0001-harness/boardgame-io/results-260731.json`

Machine: WSL2, Linux 6.18.33.2-microsoft-standard-WSL2, rustc 1.97.1,
`--release`, Criterion 1s warm-up / 3s measurement.

## 1. Scoreboard

| Metric | Target | Measured | Verdict |
|---|---|---|---|
| AM-1 rule coverage | 100% of GR-rules | 58/58 (100%) | **met** |
| AM-4a dep weight, shipped runtime | ≤250,000 third-party lines | 246,250 (23 crates) | **met** |
| AM-4b dep weight, dev toolchain | ≤350,000 third-party lines | 317,021 (29 crates) | **met** |
| AM-6 throughput | ≥100,000 events/s | 1,651,400 events/s | **met, 16.5×** |
| AM-7 scaling | ≥0.9× at 20× workload | 1.08× | **met** |
| AM-7 replay | 100k events ≤5s | 4.13 ms | **met, 1,210×** |
| AM-8 determinism | zero divergence, 10 replays | 1 distinct hash / 10 runs | **met** |
| AM-8 lint | fmt + clippy clean | clean, `-D warnings` | **met** |
| AM-10 foreign types | zero `HashMap`/`HashSet` | 0 | **met** |
| AM-11 impl pairs | null + reference per port | 1 of 1 (`KernelRng`) | **met, narrow** |
| AM-12 cost | per-task USD | $248.46 session; per-task pending | **partial** |

AM-2, AM-3, AM-5 and AM-9 are not reported: see §6.

## 2. Throughput and scaling (AM-6, AM-7)

Workload: 3-player GROUND rounds, 7 commands and 13 events per round
(12 on a game's fifth round, where GR-R09 ends the game). Pinned by
`bench_shape` in `games/ground/src/lib.rs`, so a change to the workload
breaks the test rather than silently rescaling the metric.

| Rounds | Throughput (events/s) | vs 5k |
|---|---|---|
| 5,000 | 1,524,200 | 1.00× |
| 10,000 | 1,638,200 | 1.07× |
| 20,000 | 1,577,000 | 1.03× |
| 40,000 | 1,626,000 | 1.07× |
| 100,000 | 1,651,400 | 1.08× |

Replay — folding one growing event log back into state:

| Events | Time | Rate |
|---|---|---|
| 10,010 | 465 µs | 21.5M events/s |
| 100,007 | 4.13 ms | 24.2M events/s |

### The comparison against boardgame.io, stated carefully

boardgame.io measured **1,930 moves/s at 5,000 moves**, falling to
**870 moves/s at 20,000**, and **did not finish 100,000 moves in 300 s**.
Our figure in the same unit is ~129,000 rounds/s × 7 = **~903,000
commands/s**, and 100,000 rounds complete in 776 ms.

That is roughly a 400–500× ratio, and it is **not a like-for-like
measurement**. Four differences matter, all favouring us:

1. **Different language and process model.** Rust in-process against
   Node.js with immutable state, patch generation and undo history.
2. **Different feature set.** boardgame.io's per-move cost includes
   producing client patches and maintaining undo state; the run with
   `--disable-undo` still degraded (0.66× at 40k). We do neither.
3. **Different workload shape.** Our 5-round games (GR-R09) bound state
   size by construction. The boardgame.io harness ran one match with
   unbounded history, which is exactly the axis it degraded on.
4. **No network or storage layer** on our side.

Point 3 is the important one and it is why the flat curve in the table
above is *weak evidence on its own* — a game that resets every five
rounds cannot exhibit history-growth degradation. The replay benchmark
is the honest test of that axis, because there the log grows without
bound, and it stays linear (21.5M → 24.2M events/s from 10k to 100k).

**Claim we are willing to defend:** the kernel meets AM-6 and AM-7 with
large margin, and does not degrade as event-log length grows.
**Claim we are not making:** that Clay-Borg is ~450× "faster than
boardgame.io" as a like-for-like engine comparison. Per the
InnerLoop parity-cap rule, a cross-runtime ratio this coarse is not a
verdict, it is a direction.

### A measurement error found and corrected

The first run of this benchmark reported **9.3M events/s with a
perfectly flat curve** — a number that would have been reported as a
93× beat of AM-6. It was wrong. The workload had P2 selecting SUPPORT
every round while being attacked; after three rounds P2 sat at Stress 4,
GR-R03 rejected the SUPPORT, the round never completed, and the loop
spun on rejected commands. Throughput was computed as
`rounds × 13 events` while most rounds produced 2.

Found by a probe test asserting that a round produces events at all.
The benchmark now asserts the per-round event count on every round and
panics rather than measuring a stalled loop. The corrected figure is
**5.6× lower** than the bogus one.

## 3. Determinism (AM-8)

- Every scenario runs twice per invocation with the same seed and fails
  on state-hash divergence (K8). 21/21 pass.
- Ten consecutive full runs of all 21 scenarios produced **one distinct
  output hash**, i.e. zero divergence.
- `cargo fmt --check` and `cargo clippy --workspace --all-targets
  -D warnings` are clean.
- `clippy.toml` denies `HashMap`/`HashSet` workspace-wide (K6); the
  aggregate holds only ordered collections, so iteration order cannot
  vary between runs.

## 4. AM-4 — remediated and re-measured

**Original result: NOT MET, 33 transitive crates against a ≤20 target.**
Resolved by adopting both remediations (maintainer decision,
2026-07-31): `serde_yaml` was made optional, and the metric was
retargeted onto third-party source under audit.

### Re-measurement (`make dep-weight`)

| Configuration | Crates | Third-party LOC | Target | Verdict |
|---|---|---|---|---|
| Shipped runtime (`--no-default-features`) | 23 | 246,250 | ≤250,000 | **met** |
| Dev toolchain (default features) | 29 | 317,021 | ≤350,000 | **met** |
| Our own source | — | 3,408 | — | — |

Scenario tooling costs **70,771 lines that a shipped game never
compiles**. That split is the substantive result: the single number
previously reported conflated a runtime concern with a test concern.

**What actually changed in the build.** `cb-game-runtime` gained a
`scenarios` feature carrying `serde_yaml`; the scenario module, the
`ScenarioGame` impl and the string parsers behind it are `#[cfg]`-gated.
Both configurations compile and lint clean under `-D warnings`.

One trap worth recording: setting `default-features = false` on a
*member* dependency is silently ignored when the workspace dependency
does not specify it, so the first attempt gated nothing while appearing
to work — `cargo tree` still showed all six YAML crates. The fix was
setting `default-features = false` on the workspace dependency itself,
with `cb-sim` opting into `scenarios` explicitly. This is exactly the
class of error InnerLoop v1.0's positive-control rule targets: the build
succeeded and the feature flag looked applied. It was caught by checking
the dependency graph rather than trusting that the edit had worked.

### Why the target moved, and why that is not moving the goalposts

The ≤20 crate target was retired for two measured reasons, both
recorded before the decision was taken:

Attribution:

| Group | Crates | Count |
|---|---|---|
| `sha2` (K7 state hashing) | sha2, digest, block-buffer, crypto-common, generic-array, typenum, cpufeatures, cfg-if | 8 |
| serde derive chain | serde_derive, proc-macro2, quote, syn, unicode-ident | 5 |
| serde runtime + json | serde, serde_core, serde_json, itoa, memchr, zmij | 6 |
| `serde_yaml` (scenario files only) | serde_yaml, unsafe-libyaml, indexmap, hashbrown, equivalent, ryu | 6 |
| `rand_chacha` (K5 seeded RNG) | rand_chacha, rand_core, ppv-lite86, zerocopy | 4 |
| Clay-Borg crates | cb-kernel, cb-events, cb-game-runtime, games-ground | 4 |

1. **It was unreachable without undoing the spec's own contracts.**
   Measured ladder: `serde_yaml` optional −6 (→27), dropping
   `serde_json` −4 (→23), inlining SHA-256 −8 (→19), inlining ChaCha12
   −4 (→15). Nothing reaches 20 except reimplementing a primitive that
   K5 or K7 requires — trading an audited implementation for a
   scoreboard number.
2. **Crate count does not compare across ecosystems.** Rust splits
   crates far more finely than npm. The same granularity difference made
   "33 vs 120 npm packages" flatter us *and* made ≤20 punish us.

Third-party source under audit is what the count was proxying for, is
comparable across ecosystems, and cannot be gamed by granularity. The
new targets are set at roughly the current measurement plus headroom,
so they bind on future growth rather than retroactively passing
something that failed: adding another `serde_yaml`-sized dependency to
the shipped runtime would breach AM-4a.

What we did **not** do: hand-roll SHA-256 or ChaCha to win a count.

## 5. Cost log (AM-12)

Per `specs/MetricsAndScenarios.md` §1a. Model: Claude Fable 5, at
`benchmarks/baselines/model-prices.toml` rates ($10/$50 per MTok).

| Task | Model | Iterations | Notes |
|---|---|---|---|
| CB-WP-0001 (whole session, T01–T09) | claude-fable-5 | 6 T08 code iterations + benchmarks | $248.46 measured; per-task split pending CB-WP-0002 |

**Correction (2026-07-31).** This section originally recorded AM-12 as
*uncomputable*. That was wrong. The declining to estimate was right; the
conclusion that no instrument existed was not. Every session transcript
(`~/.claude/projects/<slug>/<session>.jsonl`) carries exact per-message
`usage` including the cache breakdown. Read for this session:

| Component | Tokens | Cost (Fable 5) |
|---|---|---|
| Output | 585,528 | $29.28 |
| Cache read | 131,863,164 | $131.86 |
| Cache write (1h) | 4,365,668 | $87.31 |
| Input | 1,090 | $0.01 |
| **Session total** | | **$248.46** (~$124 on Opus 5) |

**53% of the cost is cache reads**, not output. Cost in an agentic loop
is driven by context size × turn count, which no "tokens per task"
metric would have surfaced.

Still missing is *attribution*: this is a whole-session figure, not a
per-task one, because nothing marks task boundaries in the transcript.
That is what CB-WP-0002 is for. The AM-12 row above should be read as
"session-level cost measured; per-task attribution pending CB-WP-0002".

## 6. Metrics not reported

- **AM-2, AM-3, AM-5** — specification-quality metrics that need a
  second capability to compare against; a single data point is not a
  measurement.
- **AM-9 (≤64MB)** — not instrumented. The aggregate is a few KB and
  the largest log measured here is 100k events, so the budget is very
  unlikely to bind, but "unlikely" is not "measured" and it is left
  unclaimed.
- **AM-11** — the `KernelRng` null/reference pair exists and is
  exercised. It is the only port with a pair so far, so the metric is
  met narrowly and will mean more once storage has one.

## 7. Rules implemented under a provisional default

Ten U-items in `specs/GroundRules.md` carry PROVISIONAL defaults. Those
realized here are U2 (clamp on every application), U3 (DENY with no
legal target is a no-op that still advances), U4 (deck reshuffle), U5
(REVERSE owner relief applies whether or not the Reverse was rejected)
and U8 (GROUND—OU cancellation precedes Protection).

One further ambiguity was found during T08 and is **not** in the U-list:
**GR-E02's "successes"** is undefined in dataset 0.1. It is implemented
as the count of claimed Problems. Both scoring scenarios are marked
`provisional: true`.

All provisional behaviour lives behind named functions and is covered by
scenarios tagged `provisional: true`, so a ground-game ruling flips a
scenario rather than the kernel (K16). **Action for ground-game:** rule
on the ten U-items and on GR-E02's "successes".