clay-borg/history/260801-cb-wp-0006-log.md

# CB-WP-0006 — delivery log

Per-task delivery notes, moved out of
[the workplan](../workplans/CB-WP-0006-instrument-the-table.md) when it
crossed the ~400-line loadability limit for the third time in this
project. The workplan holds the plan; this holds what happened. T08
draws on both.

## CB-WP-0006-T01

**Delivered.** `am6_throughput_clears_the_spec_target` in
`games/ground/src/lib.rs` — a test, not a bench. Best of 3 samples of
50,000 applied events each.

Measured on bnt-lap001 2026-07-31: **341,280 ev/s in debug (3.4× the
target)**, ~2.4–3.1M in release (~24–30×). **The spec target holds even in
an unoptimized build**, so the gate needed no `cfg` split and runs in the
ordinary `make test`.

**The trap was avoided by construction, not by intention.** The threshold
is the spec value `100_000`, untouched; the constant carries a comment
saying lowering it requires an ADR; and the failure message repeats that,
states the measured headroom, and names the reference figures — so a
future agent hitting a red AM-6 is told not to tune it, in the place they
will actually be reading. Robustness comes from **best-of-N**, not from a
lower bar: a throughput *floor* asks "is this machine capable", so
transient load should not fail the build.

Two positive controls in the test itself: a run that applied fewer than
50,000 events, or measured zero elapsed time, fails rather than scoring as
infinite throughput.

**Verified:** `make mutation-check --row AM-6` → **red**, via a *property*
mutation (4,000 `black_box` iterations injected into `GroundState::fold`,
the hot path) rather than a threshold tweak — raising the target would only
prove the comparison runs.

**And the FA class is now gated.** `mutation-check` rows gained an
`expect` field: the mutant's output must contain the row's stated failure
string, or the verdict is **`WRONG-REASON`**, not `red`. Without it, a
mutation that merely failed to compile would credit its row with an
assertion it does not have. Verified by pointing `expect` at a string the
verifier never prints and confirming the verdict flips. This is
remedy (2) from the CB-WP-0005 retrospective, built one task earlier than
T08 planned because the class it guards is the newest and the most
dangerous.

**M-D1-MUT: 4 → 5 of 14.**

## CB-WP-0006-T02

**Delivered — but the two rows resolved differently, and the difference is
the point.**

**AM-2 is instrumented and enforced.** `tools/size-metrics.py` +
`make size-metrics`, in `make all`:

```text
AM-2: 27.2 LOC/rule  [ok  target <= 40]  (1.47x headroom)
      1,575 code lines before the first #[cfg(test)] / 58 numbered rules
```

Tests are excluded because AM-2 asks what a rule *costs*, not how much it
is exercised — `lib.rs` is ~18% test code and including it would have
flattered the number. Verified red by a **property** mutation: ~800 lines
of filler injected into the impl, pushing the ratio past 40. `expect` is
the precise failure signature `FAIL target <= 40`, not the row name, which
would have matched passing output too.

**AM-3 is BLOCKED, not uninstrumented — and this is a finding, not a
deferral.** The row measures "LOC to express the CB-RES-0001 synthetic
game on our kernel" against a boardgame.io baseline of ~36 LOC for a
declarative **3p commit/reveal game object**. That artifact has never been
built: `games/` contains only `ground`, and `benches/synthetic.rs`
*drives* GROUND rather than *defining* a synthetic game.

Measuring GROUND's 1,575 impl lines against a 36-line synthetic game
object would compare **two different games** and call the difference a D1
result. So the tool ships the measurement mechanism — a marker-delimited
`// AM-3:BEGIN` / `// AM-3:END` region, self-tested — and **reports the row
blocked, naming the missing artifact**. A number here would have been
worse than a blank.

It therefore stays `unmutatable` and **still counts against M-D1-MUT**, per
ADR-0005 §1: a row that cannot fail asserts nothing, however good the
reason. Resolving it needs an artifact, not a metric tweak — carried
forward, not silently dropped.

**M-D1-MUT: 5 → 6 of 14.**

## CB-WP-0006-T03

**Delivered — `tools/runtime-metrics.py`. One passes, one breaches.**

**AM-9: met, and comfortably.** 13.4 MB peak RSS against a ≤64 MB target,
**4.8× headroom**. Gated and in `make all` (`--fast`, ~1 s). The row that
CB-EV-0001 called "very unlikely to bind" was right — but it is now
*measured* rather than assumed, and verified red by a property mutation
(a 300 MB allocation in the workload).

**AM-5: ~~BREACHED~~ MET — the first reading was wrong.**

> **Corrected 2026-08-01 (during T04).** T03 reported 87.0 s / 61.3 s and
> called AM-5 a 45% breach. **It is not.** Re-measured on a quiet machine
> with the fixed instrument:
>
> ```text
> load before measuring: 0.14 per CPU over 8 CPUs — quiet
> dev toolchain (default features)         37.3 s  [ok  target <= 60 s]
>   best of 3: 37.3, 42.9, 46.2  (spread 1.24x)
> shipped runtime (--no-default-features)  41.2 s  [ok  target <= 60 s]
>   best of 3: 41.2, 50.8, 54.2  (spread 1.32x)
> ```
>
> **1.6× headroom, comfortably met.** The 87.0 s was measured while the
> machine was busy running `mutation-check` and cargo builds — a timing
> measurement under contention measures the contention. That is the *same
> error class as AM-6's*, committed two tasks later in the same session,
> by the same author, in the row immediately after the one where it was
> diagnosed.
>
> The instrument now (a) reads `/proc` load average and **refuses to
> measure** above 0.5 per CPU, and (b) takes the **best of 3** — best, not
> worst, because a build-time *ceiling* asks "can this machine do it in
> 60 s", the mirror of AM-6's best-of-N for a throughput *floor*. It also
> warns when the spread exceeds 1.25×, which fired on the shipped-runtime
> samples: consecutive clean builds degrade (37.3 → 46.2), so even a quiet
> machine is not a uniform one.

The original, now-withdrawn finding follows for the record:

```text
dev toolchain (default features)             87.0 s  [FAIL target <= 60 s]
shipped runtime (--no-default-features)      61.3 s  [FAIL target <= 60 s]
```

The tool **reports and exits 0**, because the spec says the row is not
gated (and on the corrected number there is nothing to escalate anyway). Gating it is a spec change and needs an ADR; a tool that promotes
itself is how a target starts binding without anyone deciding it should.
So AM-5 stays `unmutatable` — it cannot fail while the spec declares it
ungated, which is the accurate reason. **The escalation is withdrawn**:
there is no breach to decide about.

A build profile was investigated anyway while the breach was believed
real, and the findings stand on their own: 51 compile units, 174 s of CPU
work compressed into ~54 s wall, **parallelism only 3.2× on 8 cores**
because `proc-macro2 → syn → serde_derive → serde_core` is a ~22 s serial
chain. `lto = "thin"` costs ~6 s (55.8 → 49.4 s mean) and is the only real
lever; pinning `ppv-lite86` down to drop `zerocopy` (the largest single
unit, 21.8 s) makes it **worse** — 23 → 25 crates, because the older
version pulls `zerocopy-derive`. Recorded here rather than acted on: with
1.6× headroom there is nothing to buy.

**The measurement had a real bug, found by cross-validation.**
`getrusage(RUSAGE_CHILDREN)` is a high-water mark across *every* reaped
child, so it attributed `cargo`'s memory to the workload and reported
**38.2 MB for a run that used 12.3 MB** — a 3× over-report. Fixed with
`os.wait4`, which returns that specific child's rusage. The self-test now
**cross-checks against `/usr/bin/time -v`** (13.4 vs 12.4 MB), which is
the only reason the bug was visible at all: the wrong number was
plausible, passed its target, and would have been published.

That is FA in the measurement layer rather than the mutation layer — an
instrument confidently reporting a number it had not earned.

**M-D1-MUT: 6 → 7 of 14.**

## CB-WP-0006-T04

**Delivered: withdrawn from the acceptance table, retained as a
diagnostic.** `specs/GameKernel.md` §5a carries the argument.

**The ratio has no monotone better direction.** INTENT's rule is *own the
semantics; assimilate the implementation*. Rising can mean owning
semantics properly, or reimplementing what should have been assimilated.
Falling can mean good leverage, or dependency bloat. A target requires
knowing which way is better, and this metric does not.

**It is also redundant:** AM-4a/AM-4b bound the denominator and AM-2 bounds
own-source density per rule. AM-4c is a ratio of two already-targeted
quantities.

Measured at withdrawal: **1,426** own lines per 100k third-party (shipped),
**1,107** (dev). `make dep-weight` now prints both, labelled
`diagnostic, not targeted` — it was never actually reported before.

**M-D1-MUT keeps AM-4c in its denominator, deliberately**, and says so in
the output. Dropping it would move the score 7/14 → 7/13 without enforcing
anything: a score improved by deleting the question.

### A T01 correction found here

**The AM-6 gate failed inside `make all` at 38,753 ev/s against 341,280
measured in isolation — a 9× drop.** `cargo test` runs test binaries and
threads concurrently, so **a throughput assertion inside a parallel
harness measures contention, not throughput.** T01's measurement was valid
and its gate placement was not.

Fixed by running the measurement only where it is valid — `#[ignore]`,
plus `make am6` in release with `--test-threads=1`, now **2.0M ev/s,
20.2× headroom** — and *not* by lowering the target, which T01 explicitly
forbade and which would have reproduced the defect being fixed. My first
attempt did drift that way (a debug "sanity floor" of 50,000) and was
backed out: a second threshold is still a second chance to tune.

**And the mutation went `SURVIVED` on the first run after the move** —
4,000 `black_box` iterations were calibrated against debug's 3.4×
headroom and are invisible against release's 20×. Raised to 100,000; back
to `red`. A weak mutation is not a fixed property of a row: **it can
become weak when the row's measurement conditions change.**

**M-D1-MUT: 7 of 14** (unchanged — AM-4c was always going to stay
uncounted; what changed is that the reason is now correct and recorded).

## CB-WP-0006-T05

**Delivered: K9's real assertion, K11's durable format, the `LogStore`
port, and the shared conformance suites that finally earn AM-11.**

**K11 — `crates/cb-events/src/store.rs`.** Magic + version header, 4-byte
little-endian length prefix per record, append-only. Reimplemented, not
assimilated (ADR-0005 §2): no new dependency, charged to AM-4a, and
AM-4a/AM-4b are unchanged at 246,250 / 317,021 because nothing was added
to the graph.

The operative clause is **detected**, so corruption is tested, not assumed:
a tail short by one byte, a half-written length prefix, a length prefix
corrupted to claim more than the file holds, foreign magic, and a future
format version are each rejected with a distinct error. A reader that
accepts a truncated tail is worse than no format, because it silently
returns a short history that looks complete.

**The port and the suite (AM-11).** `LogStore` has two impls —
`MemLogStore` and `FileLogStore` — and **one** `conformance()` that both
are driven through. The trait carries `raw`/`set_raw` specifically so the
corruption controls live in the *shared* suite: a format contract only one
impl enforces is not a contract.

The same shape was retro-fitted to `KernelRng`, which is what AM-11
actually names. `ChaChaRng` and `NullRng` now pass one
`conformance()` asserting the properties true of both — bounds,
`draw(1) == 0`, determinism across fresh instances, and shuffle preserving
the multiset. Previously they were exercised by two *separate* tests,
which is precisely why `AM-11 | met, narrow` was never earned and ADR-0005
§4 downgraded it.

**K9 — the assertion it did not have.** *Snapshot at seq N + events
N+1..M ≡ genesis fold*, hash-compared, on `GroundState`, single-seed on
purpose (AM-7's probe folds a multi-seed log, which is not a replay of
anything; that defect is not repeated). Two positive controls: the log
must exceed 50 events, and the mid-log snapshot must **differ** from the
end state, or "apply the remainder" would be vacuous.

**Proof it works:** the exact mutation that *survived* in CB-WP-0005 —
making `Snapshot::take` discard its `EventSeq` — now fails:

```text
assertion `left == right` failed: K9: the snapshot must carry the EventSeq it includes
test result: FAILED. 0 passed; 1 failed
```

**AM-11 mutation:** break `NullRng::draw` to return its bound and the
*shared* suite fails. That is what M-D4-SWAP claims — that either impl can
be substituted — and it is exactly what two separate per-impl tests could
never demonstrate.

**M-D1-MUT: 7 → 8 of 14.** `evidence/CB-EV-0001`'s scoreboard is refreshed
with AM-2, AM-5 and AM-9 added, AM-6 moved to enforced, and the headline
total corrected from 4 to 8 — it had gone stale within the same workplan
that produced it.