P13-S27 round 15: a mutation owes the behaviour it changed, not the assertion it broke

Independent review against fa483cf. One finding, blocking, and it ran the
scan rounds 13 and 14 left outstanding.

M6 accepted "test 5 fails" and "test 9 fails" as its observations. A test
fails for every reason, not only the one under test, so an unrelated writer
rejection satisfies both exactly as well as the intended cause. M6 could
have reported success while demonstrating nothing about pin 3a's scope.

Both halves now require the mutated outcome itself. After removing pin 3a,
test 5's stale commit must be observed to succeed, and the bundle to reopen
at the new generation with the stale base present. After broadening pin 3a,
test 9's otherwise unchanged commit -- one that does not touch
canonical_base -- must be observed rejected specifically by the broadened
writer rule, named in the report, not merely erroring.

The scan is complete: M1 through M5b survive it, M6 did not. That the one
remaining instance was in M6 -- the mutation twice rewritten for
unexecutability -- is worth noting. A mutation can be made runnable and
still not be evidential.

The principle, stated once so it need not be rediscovered: the evidence a
mutation owes is the behaviour it changed, not the assertion it broke. A
broken assertion is a symptom with many possible causes; the changed
behaviour has one. Every mutation in section 4 now names an outcome rather
than a failure.

Section 7 item 4a's M6 row was widened to point at M6 rather than restate
"test 5 fails; test 9 fails", which had become the weaker of two statements
of the same requirement -- round 14's lesson applied before it could bite.

Still NOT RATIFIED, NOT DISPATCHABLE; that call is not mine to make.
Findings 9, 6, 6, 5, 4, 3, 3, 2, 2, 1, 3, 2, 1, 1, 1. Blocking 4, 4, 4, 4,
2, 3, 3, 2, 2, 1, 2, 2, 1, 1, 1. Fifteen rounds, none returning zero, but
the character of the findings has changed: round 13 found a kind never
looked for, round 14 a contradiction round 13 created, round 15 the last
instance of round 13's kind with the scan complete across every mutation.
The known unexamined surfaces are now enumerable, which they were not
before.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ps1szk2mSfgp4Cz21eVH9x

spec/CONTRACT_P13S27_REDUCTION_AUTHORITY.md

@@ -161,7 +161,8 @@ rows — read it off, do not restate it.
 | round 12 | 2 | 2 | **yes** |
 | round 13 | 1 | 1 | **yes** |
 | round 14 | 1 | 1 | **yes** |
-| **Total** | **48** | **35** | one amendment per row |
+| round 15 | 1 | 1 | **yes** |
+| **Total** | **49** | **36** | one amendment per row |
 
 **This block previously read "amended three times … fifteen findings so far,
 eight of them blocking"** — the round-2 figures, left standing through rounds 3
@@ -459,16 +460,39 @@ order stops at the first sentence that says "done".** Where a later round narrow
 what suffices, the earlier summary is the site most likely to contradict it and
 least likely to be searched.
 
-**What round 15 should weigh, stated against interest:** findings by round are
-**9, 6, 6, 5, 4, 3, 3, 2, 2, 1, 3, 2, 1, 1**; blocking identical but for round 1's
-tail — **…, 1, 2, 2, 1, 1**. Fourteen rounds, **none clean**, but the last two are
-single-finding rounds and **round 14's was created by round 13**, not pre-existing.
-That is the narrowest the defect stream has been. **Against it:** round 13's
-question — *what else, besides the intended defect, would make this pass?* — has
-still **not** been asked of M1–M6, M5a or M5b, and round 14 did not ask it either.
-**That scan remains outstanding and is the largest known unexamined surface.**
-**Treat "dispatchable" as a claim requiring evidence of convergence, not a status
-reached by running out of findings.**
+**Review round 15 — 2026-08-08, independent, against `fa483cf`.** **One finding,
+blocking** — and it ran the scan rounds 13 and 14 left outstanding.
+
+| # | Finding | Disposition |
+|---|---|---|
+| 1 | **M6 accepted "test 5 fails" and "test 9 fails" as its observations.** A test fails for **every** reason, not only the one under test — an unrelated writer rejection satisfies both exactly as well as the intended cause, so M6 could report success while demonstrating nothing about pin 3a's scope | Both halves now require the **mutated outcome itself**: test 5's stale commit observed to **succeed** and reopen at the new generation; test 9's unchanged inherited-base commit observed **rejected specifically by the broadened rule** |
+
+**The scan is now complete: M1–M5b survive it; M6 did not.** Round 13 found this
+shape in M7, round 14 did not run the implied scan, and round 15 did. **That the
+one remaining instance was in M6 — the mutation twice rewritten for
+unexecutability — is worth noting: a mutation can be made runnable and still not
+be evidential.**
+
+**The principle, stated once so it need not be rediscovered:** *the evidence a
+mutation owes is the behaviour it changed, not the assertion it broke.* A broken
+assertion is a symptom with many possible causes; the changed behaviour has one.
+**Every mutation in §4 now names an outcome, not a failure.**
+
+**Convergence assessment, stated against interest.** Findings by round: **9, 6, 6,
+5, 4, 3, 3, 2, 2, 1, 3, 2, 1, 1, 1**. Blocking: **4, 4, 4, 4, 2, 3, 3, 2, 2, 1, 2,
+2, 1, 1, 1**. Fifteen rounds, none returning zero. **What has changed in the last
+three is the character of the findings, not only the count:** round 13 found a
+defect of a kind never looked for, round 14 found a contradiction round 13
+created, and round 15 found the **last** instance of round 13's kind — with the
+scan reported complete across every mutation.
+
+**The known unexamined surfaces are now enumerable, which they were not before:**
+§4 has been scanned for could-this-pass-for-the-wrong-reason and is clean;
+M7's authority/base leg **remains unverifiable until S27 is implemented**, by
+construction, and is carried as an execution requirement rather than a gap in the
+document. **Treat "dispatchable" as a claim requiring evidence of convergence, not
+a status reached by running out of findings** — and note that the evidence now
+exists in a form it did not at round 11.
 
 (Was: DRAFT, BLOCKED on the format-epoch rung,
 `spec/CONTRACT_FORMAT_EPOCH_MAJOR1.md`, which at the time was ratified and in
@@ -1541,8 +1565,17 @@ pin 3b has been applied backwards, and that is a finding.
 it matters; M5b alone shows it matters but never that production reads it. The
 original mutation conflated the two because, at `381c498`, one path did both.
 
-**M6 — the writer check fires.** Remove pin 3a's commit-side validation; test 5
-must fail.
+**M6 — the writer check fires. OBSERVATIONS TIGHTENED IN ROUND 15: a failing test
+is not the evidence; the changed behaviour is.**
+
+Remove pin 3a's commit-side validation. **Test 5 failing is necessary and NOT
+sufficient** — it fails for any error at all, including an unrelated writer
+rejection that has nothing to do with pin 3a.
+
+**Observe the mutated outcome itself:** test 5's stale commit must be seen to
+**SUCCEED**, and the bundle must **reopen at the new generation with the stale
+base present**. That — not the absence of the old error — is what shows the check
+was the only thing refusing it.
 
 **Second half REPLACED IN REVIEW ROUND 2. It was unexecutable as written.**
 
@@ -1556,12 +1589,31 @@ must fail.
 > the same reachability.
 
 **As replaced — broaden rather than narrow.** Widen pin 3a to refuse a commit on
-a **base-bearing bundle regardless of whether the version matches**, then confirm
-that **test 9** — `an_unrelated_commit_on_a_base_bearing_bundle_succeeds` — starts
-failing. That state **is** reachable (test 6 establishes it), so the mutation
-runs, and it signs the same thing the original was reaching for: that *"newly
-emitted or replaced"* is a deliberate scope and not an accident of where the
-check was placed.
+a **base-bearing bundle regardless of whether the version matches**, then observe
+**test 9** — `an_unrelated_commit_on_a_base_bearing_bundle_succeeds`. That state
+**is** reachable (test 6 establishes it), so the mutation runs, and it signs the
+same thing the original was reaching for: that *"newly emitted or replaced"* is a
+deliberate scope and not an accident of where the check was placed.
+
+**Test 9 failing is necessary and NOT sufficient — ROUND 15.** Observe the
+mutated outcome itself: test 9's commit, **otherwise unchanged and not touching
+`canonical_base`**, must be seen **rejected specifically by the broadened writer
+rule** — the error the broadening introduces, on the inherited-base path, named in
+the report. **Not merely "test 9 now errors."**
+
+> **Why both halves needed this. ROUND 15 applied round 13's question to M6 —
+> "what else, besides the intended defect, would make this pass?"** Both halves
+> accepted *a failing test* as the observation, and **a test fails for every
+> reason, not only the one under test.** An unrelated writer rejection satisfies
+> "test 5 must fail" and "test 9 starts failing" exactly as well as the intended
+> cause does, so the mutation could report success while demonstrating nothing
+> about pin 3a's scope. **The evidence a mutation owes is the behaviour it
+> changed, not the assertion it broke.**
+>
+> This is the same shape as round 13's M7 finding — *an observation satisfiable
+> by something other than the thing observed* — and it was found by the scan
+> round 13's finding implied and round 14 did not run. **M1–M5b survive the same
+> scan.**
 
 > **Test 9 was added in round 3 for exactly this reason.** Round 2 wrote this
 > replacement naming a *scenario* and no *test*, so nothing asserted the
@@ -2021,7 +2073,7 @@ in §N" to a number.*
    | **M4** | **no test — none is possible.** It owes the observation that the `Default` impl **compiles**, and the explicit statement that no test can catch it. That is why pin 3's prohibition is a review rule |
    | M5a | test **10a** fails, **plus** the provenance of the asserted operand |
    | M5b | test **10b** fails with both error fields asserted, **plus** the provenance of *both* operands |
-   | M6 | test **5** fails (first half); test **9** fails (second half) |
+   | M6 | **the mutated outcomes M6 specifies for both halves** — test 5's stale commit observed to *succeed* and reopen at the new generation, and test 9's unchanged inherited-base commit observed *rejected by the broadened rule*. **A failing test is necessary and not sufficient**; counts and conditions live in M6, not here |
    | **M7** | **no test — its expected outcome is success.** It owes **every observation M7 specifies, including its control**, and confirmation that the refusals M7 names as removed were restored. **Counts, methods and file names live in M7, not here** — this cell said "all three refusals" until round 8 and "field-by-field enumeration" until round 9, each time describing a method M7 no longer used |
 
    **M4 and M7 were unsatisfiable under the previous wording.** Item 1 already