chore: mark CB-WP-0006 T08/T09 done; workplan closed 9/9

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

evidence/CB-EV-0005-instrument-the-table.md

@@ -0,0 +1,163 @@
+# CB-EV-0005: did instrumenting the acceptance table change what it enforces?
+
+research: [CB-RES-0004](../research/CB-RES-0004-replay-and-kernel-coverage.md)
+adr: [ADR-0005](../decisions/ADR-0005-assertion-coverage-and-replay.md)
+workplan: [CB-WP-0006](../workplans/CB-WP-0006-instrument-the-table.md)
+log: [260801-cb-wp-0006-log.md](../history/260801-cb-wp-0006-log.md)
+instruments: `make mutation-check`, `make coverage`, `make cost-mix`
+window: `cb-cost --since dfd0d6d` — 144 responses, **$51.52**
+
+> **Numbering correction.** CB-WP-0006 T08 says "commit
+> `evidence/CB-EV-0004`". That number was already taken by CB-WP-0005's
+> evidence. This is **CB-EV-0005**.
+
+---
+
+## Test 1 — did the enforced count rise, per row?
+
+**M-D1-MUT: 4 of 14 → 8 of 14.**
+
+| row | before | after | task |
+|---|---|---|---|
+| AM-1 | red | red | — |
+| **AM-2** | unmutatable | **red** | T02 |
+| AM-3 | unmutatable | unmutatable — **blocked**, artifact never built | T02 |
+| AM-4a / AM-4b | red | red | — |
+| AM-4c | unmutatable | unmutatable — **withdrawn**, retained in denominator | T04 |
+| AM-5 | unmutatable | unmutatable — **measured and met**, spec declares it ungated | T03 |
+| **AM-6** | unmutatable | **red** | T01 |
+| AM-7 | PARTIAL 1/3 | PARTIAL **2/3** — `hash-identical` re-earned | T06 |
+| AM-8 | PARTIAL 1/2 | PARTIAL 1/2 | — |
+| **AM-9** | unmutatable | **red** | T03 |
+| AM-10 | unmutatable | unmutatable — withdrawn | — |
+| **AM-11** | unmutatable | **red** | T05 |
+| AM-12 | red | red | — |
+
+Per-task predictions, reported against what happened:
+
+| task | predicted | measured |
+|---|---|---|
+| T01 AM-6 | `unmutatable` → `red` | **met** |
+| T02 AM-2 | instrumented | **met** |
+| T02 AM-3 | instrumented **or** restated | **restated** — blocked on an artifact, not a metric |
+| T03 AM-9 | measured | **met** |
+| T03 AM-5 | measured **or** withdrawn | **measured**, and the first reading was wrong (below) |
+| T04 AM-4c | targeted **or** dropped | **dropped**, with the argument |
+| T05 AM-11 | `unmutatable` → `red` | **met** |
+| T06 K10 | replay real, AM-7 re-earnable | **met** — hash clause re-earned |
+| T07 K14/K18 | implement **or** amend | **one of each** |
+
+**The honest denominator, both ways.** 8 of 14 is 57%. But four rows
+*cannot* be enforced — AM-3 is blocked on an artifact, AM-4c is withdrawn,
+AM-5 is declared ungated by the spec, AM-10 is withdrawn — and two are
+partial. Of the **10 enforceable** rows, **8 are enforced**.
+
+The 14 stays the headline. AM-4c is deliberately retained in that
+denominator after withdrawal, and the tool says so on every run: *a score
+improved by deleting the question is not an improvement.*
+
+**Kernel spec→code link: 15/18 → 18/18.** With the caveat the gate prints
+every run: that is names, not assertions.
+
+## Test 2 — did any row regress from `red` to `SURVIVED`?
+
+**Yes, once, and it was caught.**
+
+In T04, moving AM-6's gate from debug to release turned its mutation
+`SURVIVED`. The 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`.
+
+The generalizable finding: **a weak mutation is not a fixed property of a
+row. It can become weak when the row's measurement conditions change** —
+without the row, the mutation, or the code being touched. That is a
+maintenance burden M-D1-MUT carries and T09 should weigh.
+
+No other row regressed. `SURVIVED` count across the final run: **0**.
+
+## Test 3 — were the new mutations strong?
+
+The workplan required every new mutation to be *shown to fail for the
+stated reason*. That is now **mechanical, not asserted**.
+
+`mutation-check` gained an `EXPECT-VACUOUS` verdict: if a row's `expect`
+string appears in **passing** output, the FA guard would accept any
+failure at all, and the row is reported broken rather than `red`.
+
+**Final run: 0 vacuous expects across all 14 rows.**
+
+This control exists because the failure it detects happened. My first
+`expect` for AM-2 was `"AM-2"` — which appears in the passing report, so
+the guard would have accepted a compile error as proof the row was
+enforced. Caught by hand in T02; caught mechanically from T08 onward.
+
+Every mutation added this pass is a **property** mutation, not a threshold
+tweak:
+
+| row | mutation | expect |
+|---|---|---|
+| AM-6 | 100,000 `black_box` iterations in `GroundState::fold` | `AM-6 UNMET` |
+| AM-2 | ~800 filler lines into the impl | `FAIL target <= 40` |
+| AM-9 | a 300 MB allocation in the workload | `FAIL target <= 64 MB` |
+| AM-11 | `NullRng::draw` returns its bound | `outside 0..` |
+
+## What the instruments caught that nothing else would
+
+Six defects, all found by a gate rather than by review:
+
+1. **AM-6's gate measured contention, not throughput** — 38,753 ev/s
+   inside `make all` against 341,280 in isolation, because `cargo test`
+   runs concurrently.
+2. **AM-5's first reading was wrong by 61%** — 87.0 s under load against
+   37.3 s quiet. Reported as a 45% breach; it is met with 1.6× headroom.
+   *Same error class as (1), committed two tasks later by the same author
+   in the row immediately after diagnosing it.*
+3. **RSS over-reported 3×** — `getrusage(RUSAGE_CHILDREN)` is a
+   high-water mark across every reaped child, so `cargo`'s memory was
+   charged to the workload. Found only by cross-checking `/usr/bin/time`.
+4. **K10's first round trip did not reproduce** — hashing a
+   `serde_json::Value` is a different canonical form than hashing the
+   typed aggregate. A round trip that recomputed its own comparison value
+   would have *passed* this.
+5. **The bench workload existed twice** — `bench_shape` kept passing
+   while `bench-test` broke on the same edit.
+6. **`facts-check` caught two spec copies going stale** within the hour
+   the numbers moved.
+
+## Cost, and a regression that matters
+
+| | CB-WP-0004 window | CB-WP-0005 | **CB-WP-0006** |
+|---|---|---|---|
+| pass cost | — | $16.03 | **$51.52** |
+| responses | — | 83 | **144** |
+| mechanical share | 26% | 38% | **50%** |
+| environment setup | 3 turns | 0 | **0** |
+| hub + workplan edits | 1 turn | 0 | **0** |
+| ad-hoc text patching | 8 turns | 11 | **45 turns, $13.79** |
+| orientation / inspect | 41 turns | 7 | **19 turns, $10.97** |
+| mean context | — | 315,170 | **493,486** |
+
+**Mechanical share rose to 50% — the highest ever recorded, above the 38%
+baseline that motivated CB-WP-0004.** This is not a tooling regression:
+environment setup and task closes are still at **zero**, two passes on.
+It is the *other* half of CB-WP-0004 T06's finding arriving in force —
+text patching and orientation never had their manual path removed, and a
+code-heavy pass is exactly where that spends.
+
+**Context is the sharper problem.** Mean 493,486 against a 200,000 target,
+up from 315,170 last pass. `specs/SessionShape.md` has stated SS-01…SS-05
+since CB-WP-0003 and **none of them has ever been enforced** — the only
+acceptance-adjacent numbers in this project with no gate at all, in a pass
+whose entire subject was ungated numbers.
+
+## Verdict
+
+| claim | status |
+|---|---|
+| enforced count rose | **confirmed** — 4 → 8 of 14, 8 of 10 enforceable |
+| kernel link complete | **confirmed** — 18/18, names only |
+| no row regressed to SURVIVED | **confirmed** — one near-miss, caught |
+| new mutations are strong | **confirmed mechanically** — 0 vacuous expects |
+| AM-3 instrumented | **not met** — blocked on an artifact, stated not hidden |
+| AM-7, AM-8 fully enforced | **not met** — partial, reported as partial |
+| the pass got cheaper | **refuted** — mechanical share rose to 50% |

history/260801-instrument-the-table-retrospective.md

@@ -0,0 +1,141 @@
+# 2026-08-01 — retrospective: is a weak mutation the new grep?
+
+CB-WP-0006 T09. The pass instrumented AM-2, AM-6, AM-9 and AM-11,
+implemented K10, K11 and K18, amended K14, withdrew AM-4c, and measured
+itself in [CB-EV-0005](../evidence/CB-EV-0005-instrument-the-table.md).
+
+## The question this task inherited
+
+> **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. Is it a real instrument, or a name-counter with extra
+> steps?**
+
+**It is a real instrument — but only because it was hardened three times
+in one pass, and it would have been a name-counter without that.**
+
+## What it took to make one mutation trustworthy
+
+The naive idea — *invert the property, require red* — is not enough. Five
+controls now stand between a mutation and a `red` verdict, and **every one
+of them exists because its failure actually occurred**:
+
+| control | verdict | the failure that motivated it |
+|---|---|---|
+| the mutation must apply | `HARNESS-BROKEN` | a stale find-string would score the baseline as the mutant |
+| the baseline must be green first | `inconclusive` | "mutant red" proves nothing if it was already red |
+| the tree must be restored, and verified | — | every later row runs against a corrupted tree |
+| the failure must match a **stated reason** | `WRONG-REASON` | a mutation that merely fails to compile would credit the row |
+| the stated reason must be **absent from passing output** | `EXPECT-VACUOUS` | my first AM-2 `expect` was `"AM-2"`, which the passing report contains |
+
+That last one is the sharpest. It means the FA guard needed a guard, and
+the failure it prevents is one I committed on the guard's second use.
+
+> **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.
+> That asymmetry is not overhead, it is the cost of a meta-instrument, and
+> a project that adds one should budget for it.
+
+## The failure mode that is still open
+
+CB-WP-0005 predicted a weak mutation would be *written* weak. This pass
+found a worse case: **a mutation can become weak without anyone touching
+it.**
+
+AM-6's 4,000 `black_box` iterations were calibrated against debug's 3.4×
+headroom. When T04 moved the gate to release — correctly, because the
+debug measurement was invalid — the same mutation became invisible against
+20× headroom and the row went `SURVIVED`. Nothing about the row, the
+mutation, or the code changed.
+
+The harness caught it, so the loop is not blind here. But it means
+**mutation strength is coupled to measurement conditions**, and a mutation
+is not a write-once artifact. That is a standing maintenance cost, and it
+is the honest answer to "is this cheaper than it looks": no.
+
+**CB-WP-0005 T08's stronger remedy — mutations written by someone other
+than the author of the assertion — was not tested.** The adversarial
+reviewer wrote none of these. `EXPECT-VACUOUS` covers the cheap failure
+(a guard that matches everything); it does **not** cover the expensive one
+(a mutation too weak to trip a real threshold), which is exactly what
+AM-6 demonstrated. That remedy remains untested and should not be assumed
+unnecessary.
+
+## Did the "removes the manual path" test predict which gates work?
+
+No, and this pass is the counter-example that settles it.
+
+`mutation-check` fails that test outright — `grep` is still one keystroke
+away, and a weak mutation is as easy to write as a strong one. It also
+produced **six defects nothing else would have found**: AM-6 measuring
+contention, AM-5's 61% measurement error, RSS over-reported 3×, K10's
+first round trip not reproducing, the bench workload existing twice, and
+two spec copies going stale.
+
+CB-WP-0004 T06 said tooling recovers capacity only where it removes the
+manual path. **That is a predictor of whether a gate saves money, not of
+whether it is worth having** — a correction first stated in CB-WP-0005 T08
+and now supported by a full pass. `mutation-check` costs money and earns
+its place on findings.
+
+## The cost result refutes the pass
+
+**Mechanical share rose to 50%** — the highest recorded, above the 38%
+baseline that motivated CB-WP-0004. Mean context **493,486** against a
+200,000 target, up from 315,170.
+
+This is not a tooling regression, and the distinction matters: environment
+setup and task closes are still at **zero**, two passes on. It is the
+*other* half of T06's mechanism arriving in force. Text patching (45
+turns, $13.79) and orientation (19 turns, $10.97) never had their manual
+path removed, and a code-heavy pass is precisely where that spends.
+
+So the mechanism holds in both directions, which is the strongest evidence
+it is real: what was removed stayed removed; what was merely improved
+stayed expensive, and got worse under load.
+
+## Prediction discipline, third outing
+
+| pass | prediction | measured | error |
+|---|---|---|---|
+| CB-WP-0004 | 25–30 points recovered | 6 | 4–5× |
+| CB-WP-0005 | ≥10 of 14 rows | 4 | 2.5× |
+| **CB-WP-0006** | **9 per-task outcomes** | **7 met, 2 restated with an argument** | **small** |
+
+The first two were aggregate predictions with a confidence label. This
+pass predicted **per task, as a mechanism, with the alternative named** —
+"instrument it, *or* restate it with an argument" — and the error
+collapsed.
+
+That is CB-WP-0004 T06's recommendation working. It also shows why:
+a per-task prediction with a named alternative cannot be dodged, because
+*both* branches are outcomes someone has to defend. AM-3 and AM-4c both
+took the second branch, and both are better resolved than if a number had
+been forced.
+
+## What the loop should change
+
+**Nothing in InnerLoop this pass.** v1.4's mutation requirement was added
+by CB-WP-0005 and this pass is its first full exercise; changing it again
+before a second use would be the invention-in-isolation INTENT warns
+about, and the same argument used to amend K14 four hours ago.
+
+**The named next candidate is `specs/SessionShape.md`.** SS-01…SS-05 have
+been stated since CB-WP-0003 and **none has ever been enforced** — they
+are the only acceptance-adjacent numbers in this project with no gate at
+all. Measured this pass: mean context 493,486 (target 200,000), p90
+594,888 (target 300,000), batching well under target. A pass whose entire
+subject was ungated numbers ran at 2.5× the context ceiling its own spec
+sets, and nothing said a word.
+
+## Open, not closed
+
+- **AM-3 blocked** on an artifact that has never been built — a minimal
+  synthetic game on our kernel. Needs a deliverable, not a metric tweak.
+- **AM-7 and AM-8 remain PARTIAL**: no code computes AM-7's throughput
+  ratio, and nothing enforces AM-8's N=10.
+- **`CommitWindow` is provisional with a delete-by date of 2026-12-31.**
+- **The kernel gate binds 2026-08-31** — 18/18 today, so it binds green.
+- **SessionShape is ungated**, and is now the largest measured gap.
+- **The chaos roll is at declaration 3 of 12** (T04 rolled d4=2).

tools/mutation-check.py

@@ -282,10 +282,20 @@ def check_row(row):
 
     # Positive control 2: the baseline must be green, or "mutant red"
     # proves nothing.
-    base_ok, base_tail, _ = run(row.verify)
+    base_ok, base_tail, base_out = run(row.verify)
     if not base_ok:
         return "inconclusive", f"baseline already red: {base_tail}"
 
+    # CB-WP-0006 T08: the FA guard is only a guard if its `expect` string
+    # cannot appear in PASSING output. An expect of "AM-2" would match the
+    # normal report and accept any failure at all — which is how the guard
+    # goes vacuous without anyone noticing. My first attempt on AM-2 did
+    # exactly that.
+    if row.expect and row.expect in base_out:
+        return "EXPECT-VACUOUS", (
+            f"expect string {row.expect!r} appears in PASSING output, so it "
+            f"would accept any failure — the FA guard is inert for this row")
+
     try:
         mutated = original.replace(old, new, 1)
         # Positive control 3: the file content must actually differ.
@@ -337,12 +347,13 @@ def report(only=None):
                 detail = (f"{len(r.clauses) - len(unmet)}/{len(r.clauses)} "
                           f"clauses enforced")
         tally[verdict] = tally.get(verdict, 0) + 1
-        if verdict == "HARNESS-BROKEN":
+        if verdict in ("HARNESS-BROKEN", "EXPECT-VACUOUS"):
             broken.append(r.id)
         mark = {"red": "red        ", "SURVIVED": "SURVIVED   ",
                 "unmutatable": "unmutatable", "inconclusive": "inconclusive",
                 "PARTIAL": "PARTIAL    ",
                 "HARNESS-BROKEN": "BROKEN     ",
+                "EXPECT-VACUOUS": "EXPECT-VOID",
                 "WRONG-REASON": "WRONG-REASON"}[verdict]
         print(f"  [{mark}] {r.id:<6} {r.claim[:52]}")
         if detail:
@@ -366,8 +377,8 @@ def report(only=None):
         print(f"    ({withdrawn} withdrawn row(s) retained in the denominator "
               f"on purpose — a score\n     improved by deleting the question "
               f"is not an improvement)")
-    for k in ("PARTIAL", "SURVIVED", "WRONG-REASON", "unmutatable",
-              "inconclusive"):
+    for k in ("PARTIAL", "SURVIVED", "WRONG-REASON", "EXPECT-VACUOUS",
+              "unmutatable", "inconclusive"):
         if tally.get(k):
             print(f"    {k:<13} {tally[k]}")
     if only:

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

@@ -1,7 +1,7 @@
 ---
 id: CB-WP-0006
 title: "Instrument the acceptance table, then implement what it exposes"
-status: in_progress
+status: done
 state_hub_workstream_id: "8a6327cc-fd5c-4e2c-a29b-b437c27d1e71"
 ---
 
@@ -222,14 +222,23 @@ right for K18.
 
 ```task
 id: CB-WP-0006-T08
-status: todo
+status: done
 priority: high
 state_hub_task_id: "1d4455c3-c642-47d8-916b-ab35bc512207"
 ```
 
-Commit `evidence/CB-EV-0004`. The baseline is **4 of 14**, committed and
+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
@@ -246,7 +255,7 @@ Three tests, all reported:
 
 ```task
 id: CB-WP-0006-T09
-status: todo
+status: done
 priority: medium
 state_hub_task_id: "4f291d5a-90f0-4f1f-bcaf-7ec28856bfcf"
 ```
@@ -268,3 +277,33 @@ 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.