P13-S27 round 4: the M5 pair was defective a third time

Independent review against 53292f6. Five findings, four blocking. Round 4
accepted pin 3's capabilities() accessor as bounded -- the first new text
any round has passed -- and rejected both halves of M5 again.

M5b cited the wrong value, and this one is mine. roundtrip.rs:367 sits in
assert_score_serialization_stable, not assert_reduction_serialization_stable,
and it versions an acceleration snapshot, not a canonical base. The latter
has no base at all, because pin 3c suspended it. So the value round 3 told
the implementer not to touch was irrelevant to the authority check, and
mutating it could not have failed anything. Round 3 grepped
ReductionAlgorithmVersion across testkit/src/, saw a roundtrip.rs hit, and
attributed it to the function it was already thinking about without
resolving the enclosing item -- the same shape as section 0.4's .commit(
miscount, which round 1 had already recorded as a lesson. Recording a
defect is not the same as not committing it. The tautology diagnosis
stands; only its evidence was wrong.

M5b left the instrument unchosen. Round 3 said "the rung picks one" and
named two routes, one of which does not exist for the nominated crate:
craft_image_with_base is a private fn inside epiphany-bundle's cfg(test)
module. Now chosen, through public API only: build with
synthetic_for_fixture(0), commit a base carrying the literal 0, take the
bytes, reopen under the real constant. The operands are provably
independent and neither can be tidied into the other.

M5b had no test that could assert the error fields.
assert_reduction_serialization_stable returns () and reopens with .expect,
so a mismatch panics instead of yielding a matchable
CanonicalBaseRequiresRebuild { base, current }. Test 10b added, named and
returning a matchable Result.

M5a violated section 7 item 4a -- the rule round 3 added in the same edit.
It named no test, and its natural assertion compares
CURRENT_REDUCTION_ALGORITHM_VERSION with itself, which holds for every
value. Test 10a added, asserting against a deliberate literal. Round 3
diagnosed M5b's tautology and wrote the identical tautology into M5a in the
same edit, then added a rule and immediately broke it.

Both literals are load-bearing as literals. Section 7 item 4b now requires
confirming neither was rewritten as the constant -- tidying either makes
its mutation vacuous while every test stays green.

Minor: status prose said the pins were open to round 3's findings after
round 3 closed.

Still NOT RATIFIED, NOT DISPATCHABLE. Defect rate 9, 6, 6, 5 -- not
converging, and every blocking finding in rounds 3 and 4 was in text
written to fix the previous round.

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

@@ -1,9 +1,9 @@
 # Contract — P13-S27: the reduction version gets an outside witness
 
-**Status:** **NOT RATIFIED. NOT DISPATCHABLE.** Independent **review round 3
-closed** against `b842975` — six findings, four blocking, all now carried.
-**Awaiting review round 4**; the pins remain open and no execution work may
-begin.
+**Status:** **NOT RATIFIED. NOT DISPATCHABLE.** Independent **review rounds 3 and
+4 closed** — six findings then five, eight blocking between them, all now
+carried. **Awaiting review round 5**; the pins remain open and no execution work
+may begin.
 
 **Round 1's ratification is WITHDRAWN.** It was claimed on 2026-08-07 after a
 single round; round 2 then found four more blocking defects against the
@@ -12,8 +12,10 @@ ratification that a subsequent round falsifies that quickly was not a
 ratification, and leaving the claim standing would make the status field mean
 nothing.
 
-**The pins are therefore NOT frozen.** They are open to round 3's findings.
-Freezing follows ratification; it does not precede it, and it does not survive a
+**The pins are therefore NOT frozen.** They are open to **the current round's**
+findings — rounds 3 and 4 are closed, and this sentence named a specific round
+until round 4 caught it going stale the moment that round closed. Freezing
+follows ratification; it does not precede it, and it does not survive a
 withdrawal. **No execution work may begin** — not implementation, not staging,
 not partial work against "the settled pins."
 
@@ -44,14 +46,38 @@ mutation is easy; establishing that it *can run* requires deriving its
 observation, its failure condition, and the test it breaks, and none of the three
 was done. §7 item 4a now demands all three.
 
-**What round 4 should weigh, stated against interest:** the defect rate is **not
-converging** — nine, six, six — and every blocking finding in round 3 was in text
-written to fix round 2's findings. **The amendment process has produced defects
-at a steady rate for three rounds.** The newest text — pin 3's accessor, M5a,
-M5b, test 9, row 7a — has had **zero** adversarial passes and was written by the
-same agent whose previous two attempts round 3 just falsified. **Treat
-"dispatchable" as a claim requiring evidence of convergence, not a status reached
-by running out of findings.**
+**Review round 4 — 2026-08-07, independent, against `53292f6`.** Five findings,
+four blocking. It judged pin 3's accessor **bounded** — the first piece of new
+text any round has accepted — and the M5 pair defective again.
+
+| # | Finding | Disposition |
+|---|---|---|
+| 1 | **M5b cited the wrong value.** `roundtrip.rs:367` is in `assert_score_serialization_stable` (`:332`) and versions an **acceleration snapshot**, not the canonical base. `assert_reduction_serialization_stable` has **no base at all** — pin 3c suspended it | Evidence corrected. **The tautology diagnosis stands; only its evidence was wrong** |
+| 2 | **M5b left the instrument unchosen** — it said "the rung picks one" and named two, one of which does not exist for the nominated crate: `craft_image_with_base` is private to `epiphany-bundle`'s test module (`:1648`) | **Chosen**: commit-then-reopen through public API only |
+| 3 | **M5b had no test that could assert the error fields.** `assert_reduction_serialization_stable` returns `()` and reopens with `.expect` (`:292`) — a mismatch panics and cannot match `CanonicalBaseRequiresRebuild { base, current }` | **Test 10b** added, named and returning a matchable `Result` |
+| 4 | **M5a violated §7 item 4a — the rule round 3 added in the same edit.** It named no test, and its natural assertion (`capabilities() == CURRENT_REDUCTION_ALGORITHM_VERSION`) compares the constant with itself and cannot fail | **Test 10a** added; the comparison is now against a deliberate **literal** |
+| — | Status prose said the pins were open to *round 3's* findings after round 3 closed | Now "the current round's" |
+
+**Round 3's error is the one to carry.** It grepped `ReductionAlgorithmVersion`
+across `testkit/src/`, saw a `roundtrip.rs` hit, and attributed it to the function
+it was already thinking about **without resolving the enclosing item** — the same
+shape as §0.4's `.commit(` miscount, which round 1 recorded as a lesson and round
+3 then repeated. **Recording a defect is not the same as not committing it.**
+
+**And both M5 halves failed the same way twice.** Round 3 diagnosed M5b's
+tautology and wrote M5a with an identical tautology *in the same edit*, then
+added §7 item 4a and immediately violated it. A rule written and broken in one
+sitting is evidence the author is pattern-matching the finding rather than
+applying it.
+
+**What round 5 should weigh, stated against interest:** the defect rate is **nine,
+six, six, five** — still not converging after four rounds, though round 4 accepted
+its first piece of new text. **Every blocking finding in rounds 3 and 4 was in
+text written to fix the previous round.** The newest material — tests 10a/10b,
+M5b's chosen instrument, §7 item 4b — has had **zero** adversarial passes, and the
+M5 pair has now been rewritten **three times** and found defective each time.
+**Treat "dispatchable" as a claim requiring evidence of convergence, not a status
+reached by running out of findings.**
 
 (Was: DRAFT, BLOCKED on the format-epoch rung,
 `spec/CONTRACT_FORMAT_EPOCH_MAJOR1.md`, which at the time was ratified and in
@@ -852,6 +878,35 @@ the ruling recorded beside it.)*
    asserting the behaviour it breaks. **A mutation is only as good as the test it
    breaks**, and §4 must name that test for every entry.
 
+**Added in review round 4 — the two tests M5a and M5b break. Round 3 wrote both
+mutations without them, in the same edit that added §7 item 4a requiring them.**
+
+10a. **`serialize_document_supplies_the_real_reduction_authority`** — in
+   `epiphany-textproj`. Serialize a base-free document and assert
+   `bundle.capabilities().current_reduction_version == ReductionAlgorithmVersion(0)`.
+
+   **The `0` MUST be a literal, and the test MUST carry a comment saying why.**
+   Comparing against `CURRENT_REDUCTION_ALGORITHM_VERSION` would compare the
+   constant with itself and hold for every value — the assertion would be
+   unfalsifiable and M5a could not break it. **This test is expected to fail when
+   S16 bumps the authority**, and that is correct: the literal is a tripwire on
+   the production wiring, and S16 updating it is S16 stating that it moved.
+
+10b. **`a_base_bearing_bundle_reopened_under_the_real_authority_validates`** — in
+   `epiphany-testkit`, which may use the real constant. Build the fixture with
+   `synthetic_for_fixture(0)`, commit a base carrying the literal
+   `ReductionAlgorithmVersion(0)`, take the bytes, and reopen them with `caps`
+   built from `CURRENT_REDUCTION_ALGORITHM_VERSION`. Assert it opens.
+
+   **This is the only place in the rung where the real authority meets a
+   canonical base**, which is why M5b needs it and why no existing test could
+   serve. It must be a named test returning a matchable `Result`, **not** an
+   assertion inside a void conformance helper.
+
+**Both literals are load-bearing as literals.** A later reader "tidying" either
+into `CURRENT_REDUCTION_ALGORITHM_VERSION` makes the corresponding mutation
+vacuous while leaving every test green. Say so in both doc comments.
+
 Tests 2 and 3 must be **paired in review**: each asserts the other's error is
 *not* produced. A test that only checks its own variant cannot show the two
 paths are distinguishable, which is the whole point of pin 6.
@@ -926,9 +981,21 @@ REVIEW ROUND 3.**
 > observation depends on scaffolding that is not in the shipped tree observes the
 > scaffolding, not the tree.
 
-Change `CURRENT_REDUCTION_ALGORITHM_VERSION`. In a test over
-`serialize_document`, assert via **`bundle.capabilities().current_reduction_version`**
-that the value the production path supplied moved with the constant.
+**The test it breaks is test 10a** (§3), and the comparison **MUST be against a
+literal, not against the constant. CORRECTED IN ROUND 4.**
+
+> **Round 3 wrote "assert that the value moved with the constant", which is
+> unfalsifiable.** Asserting `capabilities() == CURRENT_REDUCTION_ALGORITHM_VERSION`
+> compares the constant with itself laundered through one function call: mutate
+> the constant and **both sides move**, so the assertion holds for every value.
+> That is the same tautology round 3 caught in M5b, in the mutation *next to it*,
+> written in the same edit. Round 3 also violated its own new §7 item 4a by
+> naming no test at all.
+
+Change `CURRENT_REDUCTION_ALGORITHM_VERSION` from `0` to any other value. Test
+10a must **fail**, because it asserts
+`bundle.capabilities().current_reduction_version == ReductionAlgorithmVersion(0)`
+with `0` written as a **deliberate literal** — the independent operand.
 
 Assert on the capability **only** — not on an open or commit outcome. There is no
 base, so no check fires and none should. **If an open or commit outcome moves
@@ -938,39 +1005,71 @@ and that is a finding.**
 **M5b — the authority is load-bearing where a base exists. REWRITTEN IN REVIEW
 ROUND 3; as written it could not fail.**
 
-> **This is the rung's own defect, reproduced inside the mutation built to detect
-> it.** Round 2 named `assert_reduction_serialization_stable`
-> (`testkit/src/roundtrip.rs:255`) as the failing test. But that harness stamps
-> its base version at `roundtrip.rs:367`, today a literal
-> `ReductionAlgorithmVersion(0)`, and the natural S27 implementation replaces that
-> literal with `CURRENT_REDUCTION_ALGORITHM_VERSION` **while also sourcing the
-> supplied capability from it**. Both operands then move together and the
-> comparison passes for every value of the constant — **precisely §0.1's
-> tautology**: *"both operands descend from the same source, so for any
-> conformingly-written document the comparison is a tautology."* A mutation that
-> cannot fail is not a mutation.
+> **Round 3's diagnosis was right and its evidence was wrong. CORRECTED IN ROUND
+> 4.** Round 3 said the base version was stamped at `roundtrip.rs:367`. **It is
+> not.** `:367` sits inside `assert_score_serialization_stable` (`:332`) and
+> pushes to **`acceleration_snapshots`** — a different harness and a different
+> field. `assert_reduction_serialization_stable` (`:255`) has **no canonical base
+> at all** today; pin 3c suspended it, and the harness reads its snapshot chunk
+> directly by `ChunkRef`. So the value round 3 told the implementer not to touch
+> has nothing to do with the authority check, and mutating it could not have
+> failed anything.
+>
+> **How the error was made, since it is this rung's own subject:** round 3 grepped
+> `ReductionAlgorithmVersion` across `testkit/src/`, saw a `roundtrip.rs` hit, and
+> attributed it to the function it was already thinking about **without resolving
+> the enclosing item**. That is the fourth instrument failure in this contract and
+> the second of exactly this shape — §0.4's `.commit(` miscount was the first.
+>
+> **The underlying tautology finding stands.** If the supplied capability and the
+> base version both descend from `CURRENT_REDUCTION_ALGORITHM_VERSION`, both
+> operands move together and the comparison passes for every value — §0.1's
+> defect inside the mutation built to detect it. Only the cited evidence was
+> wrong.
 
-**The base version MUST come from a source that does not move with the
-constant.** Two acceptable instruments, and the rung picks one and says which:
+**The instrument is CHOSEN, not offered. ROUND 4.** Round 3 said "the rung picks
+one" and named two routes, which is not a decision — and one of them does not
+exist: **`craft_image_with_base` is a private `fn` inside `epiphany-bundle`'s
+`#[cfg(test)]` module (`bundle.rs:1648`, module opens at `:1407`)**, so
+`epiphany-testkit` cannot call it. The routes also carry different fixture and
+touch-table consequences, so leaving the choice to execution would have put a
+design decision in the implementer's hands.
 
-- **a persisted artifact** — a committed fixture image whose base version is
-  fixed on disk, built via `craft_image_with_base`; or
-- **an explicit literal** in the test, written as a literal *because* it must not
-  track the authority, with a comment saying so.
+**The chosen instrument — commit-then-reopen, entirely through public API:**
 
-**What must be observed:** with the constant mutated, the capability and the base
-version now disagree, and the test fails with **`CanonicalBaseRequiresRebuild`**,
-both fields asserted. **Record the two operands' provenance in the report** —
-naming where each came from is the only way to show they are independent, and
-that independence is the whole content of this mutation.
+1. Build a bundle with `caps = synthetic_for_fixture(0)` and commit a canonical
+   base whose version is the **deliberate literal** `ReductionAlgorithmVersion(0)`.
+   This succeeds by test 8's path.
+2. Take the bytes.
+3. **Reopen them with `caps` built from the real
+   `CURRENT_REDUCTION_ALGORITHM_VERSION`.**
+
+Unmutated, the real constant is `0`, the operands agree, and the bundle opens.
+Mutated, the constant is not `0`, and the reopen fails with
+**`CanonicalBaseRequiresRebuild { base: 0, current: <mutated> }`**.
+
+**Why this shape and not another:** the two operands are provably independent —
+one is a synthetic literal written into a fixture, the other is the real constant
+read at the reopen — and **neither can be "tidied" into the other** without
+deleting the synthetic capability the fixture is built on. It needs no private
+helper, no new fixture file, and no touch-table row. It isolates the real
+constant on the **read** side only, so pin 3a's writer check cannot fire first
+and mask the result.
+
+**The test it breaks is test 10b** (§3) — a **named** test, not the void
+conformance helper. **ROUND 4:** round 3 nominated
+`assert_reduction_serialization_stable`, which returns `()` and whose reopen is
+`.expect("reopen bundle")` (`roundtrip.rs:292`). A mismatch there **panics**; it
+cannot match on `CanonicalBaseRequiresRebuild { base, current }`, so the required
+two-field assertion was impossible in the nominated site.
+
+**Report the provenance of both operands.** Naming where each came from is the
+only way to show they are independent, and that independence is the whole content
+of this mutation.
 
 **Preserved from the original M5:** if only `synthetic_for_fixture` tests move,
 pin 3b has been applied backwards, and that is a finding.
 
-> **Note for whoever implements the restoration.** `roundtrip.rs:367`'s literal
-> `0` must **not** be mechanically swapped for the constant. It is load-bearing
-> as a literal. Doing the "obvious tidy-up" there is what makes M5b vacuous.
-
 **Both halves are required.** M5a alone shows the constant is read but never that
 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.
@@ -1125,9 +1224,13 @@ in §N" to a number.*
 2. **Every gate item in §5** — currently **eight** (1, 2, 3, 4, 5, 6, 6a, 7),
    each with the command that produced it.
 3. The staged file list, and the test-count delta in gate 1's three buckets.
-4. **Every required test in §3** — currently **nine** *(test 9 added in round 3)*
-   — by name, each passing, with tests 2 and 3 shown to produce *different*
-   errors, and the same for tests 6/2 and 8/5.
+4. **Every required test in §3** — currently **eleven** (1–9 plus **10a** and
+   **10b**, added in round 4) — by name, each passing, with tests 2 and 3 shown
+   to produce *different* errors, and the same for tests 6/2 and 8/5.
+4b. **Confirmation that the literal `0` in tests 10a and 10b is still a literal**,
+   and that neither was rewritten as `CURRENT_REDUCTION_ALGORITHM_VERSION`.
+   Tidying either makes M5a or M5b vacuous while every test stays green — the
+   failure mode is invisible to the suite and visible only here.
 4a. **For every mutation in §4, the named test it breaks**, and for M5a/M5b the
    **provenance of each operand** — where the capability came from and where the
    base version came from. Three mutations were found unrunnable across rounds 2