clay-borg/workplans/CB-WP-0006-instrument-the-table.md

---
id: CB-WP-0006
kind: mixed
title: "Instrument the acceptance table, then implement what it exposes"
status: done
state_hub_workstream_id: "8a6327cc-fd5c-4e2c-a29b-b437c27d1e71"
---

# Purpose

CB-WP-0005 T02 measured M-D1-MUT for the first time:

```text
  M-D1-MUT: 4/14 rows enforced
    PARTIAL       2      (AM-7, AM-8 — some clauses live, some inert)
    unmutatable   8      (no property to invert)
```

**4 of 14, against a predicted 10 of 14.** The prediction was wrong by
2.5×, and wrong about *what* as well as *how much*: CB-RES-0004 diagnosed
three absent kernel rules, and the measurement found that **more than half
the acceptance table has no instrument behind it at all**.

CB-WP-0005 Phase C was deferred before starting on that basis (T02's stop
condition, maintainer decision 2026-07-31). It was scoped to five rules —
K9, K10, K11, K14, K18 — which does not address the eight.

This workplan is scoped to what was measured rather than what was
predicted. **Phase A instruments the unmeasured rows; Phase B implements
the kernel work inherited from CB-WP-0005 T04–T06.** That order is the
whole point: the previous pass built a fix before its instrument existed,
and the instrument then contradicted the fix's premise.

Per InnerLoop §Step 4, no target moves in the commit that measures it.

## Phase A — instrument the rows that measure nothing

## Task: AM-6 — assert the throughput target

```task
id: CB-WP-0006-T01
status: done
priority: high
state_hub_task_id: "a4513794-2f5f-480c-be30-56658711796f"
```

The sharpest single finding of CB-WP-0005. **Nothing in the workspace
compares any number to 100,000 events/s** — the project's headline
throughput claim, reported as `met, 16.5×`. The Criterion bench emits
throughput; the only asserts in `synthetic.rs` are the stress-gate shape
and the events-per-round pin.

Deliver a standing assertion — a test, not a bench — that measures applied
events/s on the synthetic workload and fails below the AM-6 target.

**The trap, stated up front:** a timing assertion in CI is flaky by
nature, and the usual response is to loosen it until it never fires, which
would reproduce exactly the defect being fixed. So the threshold is
**pinned well below the measured 1.65M/s** (AM-6 asks for 100k), the
assertion states its own headroom in the failure message, and a loosening
requires an ADR. A gate tuned until it cannot fire is a gate that counts
names.

**Verified by:** `make mutation-check --row AM-6` goes from `unmutatable`
to `red`.

**Delivered** — see [the delivery log](../history/260801-cb-wp-0006-log.md#cb-wp-0006-t01).

## Task: AM-2, AM-3 — instrument the size metrics

```task
id: CB-WP-0006-T02
status: done
priority: medium
state_hub_task_id: "d1572a4f-46e5-49dd-b1ec-7c371a780bb7"
```

AM-2 (≤40 spec lines per rule) and AM-3 (≤50 LOC for the synthetic
workload) are both `unmutatable` for the same reason: `make loc` prints
line counts and nothing divides, compares, or gates.

AM-2 is the **anti-gaming pair** for AM-1 — 100% rule coverage means
nothing if the rules are trivially small — so an uninstrumented AM-2
leaves AM-1 gameable, which is the specific risk MetricsAndScenarios §1
names when it introduces M-D1-SPL.

AM-3 depends on K18 (benches driven from scenario files); if K18 resolves
toward amending the spec rather than implementing it, AM-3 must be
restated or withdrawn with an argument rather than left unmeasured.

**Delivered** — see [the delivery log](../history/260801-cb-wp-0006-log.md#cb-wp-0006-t02).

## Task: AM-5, AM-9 — measure or withdraw, but stop leaving them blank

```task
id: CB-WP-0006-T03
status: done
priority: medium
state_hub_task_id: "6c84a220-cab3-40f1-b35f-b8df79106f6e"
```

AM-5 (clean build ≤60 s) is `recorded not gated` — and not recorded
either. AM-9 (peak RSS ≤64 MB) is declared "very unlikely to bind", which
CB-EV-0001 itself calls out as an unmeasured judgment call.

Both are cheap to measure: one `time` around a clean build, one
`/usr/bin/time -v` around the 100k-event run. **Or withdraw them with an
argument**, which is a legitimate outcome and possibly the right one for
AM-5 on a machine-dependent number. What is not legitimate is a third pass
leaving them blank while the scoreboard reports elsewhere.

**Delivered** — see [the delivery log](../history/260801-cb-wp-0006-log.md#cb-wp-0006-t03).

## Task: AM-4c — target it or drop it

```task
id: CB-WP-0006-T04
status: done
priority: low
state_hub_task_id: "a2571314-4c02-41cf-9473-96d3ae2d7b2b"
```

`reported, not targeted`, so there is no property to invert and it counts
against M-D1-MUT by ADR-0005 §1.

Two honest options, and the task must pick one with an argument: give it a
threshold (making it enforceable), or **remove it from the acceptance
table** and keep it as a reported diagnostic. A row in an acceptance table
that cannot fail is decoration, and this pass has learned to say so.

Note the incentive: ADR-0005 already predicts own-source growth from the
kernel work in Phase B, so AM-4c will move against us. Setting its
threshold *after* seeing that movement would be the retarget InnerLoop
§Step 4 forbids — so it is set here, before Phase B, or not at all.

**Delivered** — see [the delivery log](../history/260801-cb-wp-0006-log.md#cb-wp-0006-t04).

## Phase B — the kernel work inherited from CB-WP-0005

> These three were written in [CB-WP-0005](CB-WP-0005-assertion-coverage.md)
> Phase C and cancelled unstarted. Their analysis lives **here**, next to
> the work — CB-WP-0005 keeps only a forward pointer, so there is one copy.
> The normative controls are in
> [ADR-0005](../decisions/ADR-0005-assertion-coverage-and-replay.md) §6.

## Task: K9 and K11 — durable log, LogStore port, real conformance suite

```task
id: CB-WP-0006-T05
status: done
priority: high
state_hub_task_id: "2a357dbf-3861-499d-a12e-f7682b7332f6"
```

**K9** — the acceptance property is *snapshot at seq N + events N+1..M ≡
genesis fold*, hash-compared, on `GroundState`. What exists instead is one
test round-tripping a `BTreeMap<String, u8>` with `EventSeq(17)` as a
literal: no game aggregate, no events applied, no from-genesis comparison.
Mutation-proven — making `Snapshot::take` discard its `EventSeq` leaves the
test green, so the half of K9 that says "+ the EventId it includes" is
unverified. `Snapshot` has no callers outside its own test.

**K11** — append-only, length-prefixed, versioned framing, with a truncated
tail **detected**; the operative clause is *detection*, so truncate-by-one-
byte and corrupt-length-prefix rejection are required, not optional.
Reimplemented rather than assimilated (ADR-0005 §2): ~100 lines against a
format Kafka and EventStore converged on independently, adding no
dependency, charged to **AM-4a** (shipped runtime, 1.5% headroom). The `LogStore` port with a shared
`fn conformance<S: LogStore>(…)`, retro-fitted to `KernelRng`, is what
finally earns **AM-11** — currently downgraded to unmet because the pair
exists and the suite does not.

**Verified by:** `make mutation-check --row AM-11` goes from
`unmutatable` to `red`.

## Task: K10 — the replay bundle and `--replay`

```task
id: CB-WP-0006-T06
status: done
priority: high
state_hub_task_id: "d459444d-41be-40c5-9101-7a8420b42fb6"
```

INTENT design decision 8 of 10, unimplemented. `cb-sim` has no flag
parsing at all, so `--replay` has nowhere to go yet.

**This is not "a directory of four files"** — the D2 correction the
adversarial review forced. `scenario.rs` creates an `EventLog`, appends to
it and never reads it: the one production instantiation of the K11 log is a
write-only sink. `Pass` carries the *end* state, not an initial snapshot,
and failures are a formatted `String`, not structured expected-vs-actual.
Plumb the log out of `execute`, capture an initial snapshot, restructure
`RunOutcome::Failed`. The writer is **dev-only** behind the `scenarios`
feature and is charged to **AM-4b** (9.4% headroom), not AM-4a.

All four controls from ADR-0005 §6 are required verbatim, including the two
the reviewer supplied: truncate-by-one-byte rejection, and a mutated-seed
control so the round-trip is capable of failing.

Fixing this is also what lets **AM-7's withdrawn `hash-identical`
clause** be re-earned, since a real replay is what the clause was always
about.

## Task: K14 and K18 — implement, or amend the spec and say why

```task
id: CB-WP-0006-T07
status: done
priority: medium
state_hub_task_id: "d76ad893-520b-44bd-9b77-07dbfb651ce3"
```

Inherited from CB-WP-0005 T06. `CommitWindow` has zero non-test users;
the bench never touches `ScenarioFile`. Either wire them up or amend the
rules with a recorded argument. Deleting a rule to make a gate green is
forbidden; deleting one *with an argument* is legitimate and probably
right for K18.

## Phase C — measure, and answer the question this pass inherited

## Task: control loop — M-D1-MUT before and after

```task
id: CB-WP-0006-T08
status: done
priority: high
state_hub_task_id: "1d4455c3-c642-47d8-916b-ab35bc512207"
```

Commit `evidence/CB-EV-0005` — **numbering corrected**, CB-EV-0004 was
already CB-WP-0005's. The baseline is **4 of 14**, committed and
reproducible via `make mutation-check`.

**Measured — [CB-EV-0005](../evidence/CB-EV-0005-instrument-the-table.md).
4 of 14 → 8 of 14** (8 of 10 enforceable; the 14 stays the headline and
AM-4c stays in it on purpose). Kernel link 15/18 → **18/18**, names only.
One row regressed to `SURVIVED` and was caught. **0 vacuous expects**
across 14 rows — test 3 is now mechanical, via a new `EXPECT-VACUOUS`
verdict. **The cost result refutes the pass:** mechanical share rose to
**50%**, the highest recorded.

Three tests, all reported:

1. **Did the enforced count rise, per row?** Against the per-task
   predictions above, unmet reported as unmet.
2. **Did any row regress from `red` to `SURVIVED`?** The four currently
   enforced rows are the ones with something to lose.
3. **Were the new mutations strong?** CB-WP-0005 T02 wrote two no-op
   mutations on its first attempt, either of which would have published a
   false accusation against working code. Every mutation added by this
   pass must be shown to fail for the *stated* reason — record how that
   was checked.

## Task: retrospective — is a weak mutation the new grep?

```task
id: CB-WP-0006-T09
status: done
priority: medium
state_hub_task_id: "4f291d5a-90f0-4f1f-bcaf-7ec28856bfcf"
```

The question CB-WP-0005 T08 raised and this pass is positioned to answer.

CB-WP-0004 concluded that tooling recovers capacity only where it removes
the manual path. M-D1-MUT does **not** remove a manual path — writing a
weak mutation is exactly as easy as writing a strong one, and the harness
cannot tell the difference. CB-WP-0005 produced two no-op mutations on its
first attempt, so the failure mode is demonstrated, not hypothetical.

**And it fails in the more dangerous direction:** a weak mutation does not
merely miss a defect, it *indicts working code*. A false `SURVIVED` sends
the next pass to fix something that is not broken.

So: is M-D1-MUT a real instrument, or a name-counter with extra steps? If
the latter, say so and propose what would actually bind — the candidate
being that the mutation must be written by someone other than the author
of the assertion, which is the adversarial-review principle applied one
level down.

**Answered — [260801-instrument-the-table-retrospective.md](../history/260801-instrument-the-table-retrospective.md).**

**A real instrument — but only because it was hardened three times in one
pass.** Five controls now stand between a mutation and a `red` verdict,
and every one exists because its failure actually occurred. The
generalizable finding: **an instrument that measures whether other
instruments work needs more controls than the instruments it measures** —
M-D1-MUT carries five, `dep-weight` and `rule-coverage` carry one each.

**A worse failure mode than predicted:** a mutation can become weak
**without anyone touching it**. AM-6's went `SURVIVED` when T04 moved its
gate from debug to release. Mutation strength is coupled to measurement
conditions, so a mutation is not a write-once artifact. CB-WP-0005 T08's
stronger remedy — mutations written by someone other than the author —
was **not tested** and should not be assumed unnecessary: `EXPECT-VACUOUS`
covers the cheap failure, not the expensive one AM-6 demonstrated.

**Prediction error collapsed** — 4–5×, then 2.5×, now small — because this
pass predicted **per task, as a mechanism, with the alternative named**.
Both branches are outcomes someone must defend, so the prediction cannot
be dodged; AM-3 and AM-4c took the second branch and are better resolved
for it.

**No InnerLoop change.** v1.4's mutation requirement is one pass old and
changing it before a second use would be the invention-in-isolation INTENT
warns about — the same argument used to amend K14. **The named next
candidate is `specs/SessionShape.md`**: SS-01…SS-05 have never been
enforced, and this pass ran at **2.5× the context ceiling its own spec
sets** without anything saying a word.