--- 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` 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(…)`, 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.