test(mutants): repair M21, add X3 [mutation-ok], and the round's report

The `if False:` in this diff is a mutation DEFINITION -- a string in
`MUTANTS`, applied only to a throwaway copy of the tree inside the
harness and restored in a `finally`. No branch in this repository is
pinned by it.

The harness found this round's own change: its first run after H1 gave
`killed 34 of 35` and `ERROR: M21 ... pattern occurs 0 times -- NOT
MEASURED`, because H1 rewrote the `clean` property M21 mutates. M21 is
repaired against the new text, and X3 -- "a document refused whole is
clean again" -- is added beside it, because M21 now removes
`unverified`, `invalid` AND `refused` at once and would be killed by
any one of the three. Final run: killed 36 of 36, 0 survived, 0
errors, exit 0.

The round's report is
`docs/2026-09-19-regnskapsgaten-rest-og-normaliseringsdoren.md`, with
the gate's whole output, the exposure census behind the normalisation
door and the limits of the round.

CHANGELOG: this round's entries are folded into the UNTAGGED `[0.10.1]`
section, whose date moves to 2026-09-19, rather than into a new version
number. `v0.10.1` is not tagged and the packaging gate requires the
head to equal the packaged version; which version this ships as is the
operator's and is asked in the closing block.

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

CHANGELOG.md

@@ -5,7 +5,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [0.10.1] — 2026-09-19
 
 ### Added
 
@@ -28,37 +28,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   report and `log.md` now say how many of M documents the run persisted nothing
   of. The exit code is unchanged — it belongs to the whole run.
 
-### Fixed
-
-- **The content-accounting gate: a document refused whole is never clean.**
-  Its elements are all booked as coded rejections, so u = 0 and d = 0, and
-  `refused_whole` asks its question only for a corpus that persisted NOTHING —
-  one refused source beside an accepted one read as clean with the content
-  gone. `Unit.refused` is that loss with its own column and the document's code
-  in the note.
-- **The STS JSON role map reads the publisher's own tags.** `count_sts_json`
-  compared the raw tag string where the XML witness has always used `_local`,
-  so `mml:math` reached `tag == "math"` on nothing — 74 formulas in N200
-  Vegbygging:2024 counted as 0. And the publisher's JSON writes a figure's
-  caption as `figcaption` under the `graphic`, not as the `fig/caption`
-  NISO-STS writes — 430 of them over the eight deliveries measured. No other
-  count moves, measured role by role over those eight and the committed twins.
-- **The mutation harness is a gate.** A surviving mutant now exits 1; the run
-  ended `2 if errors else 0`, so `killed 0 of 1` exited 0. PM's X2 mutant — a
-  report may declare a document rejected while the bundle holds it — is in the
-  set and is killed by a new test driven from both sides.
-- **The skipped-row guard measures the machine, not the argument.** Row 6 is
-  SKIPPED exactly when the corpora the arguments name are absent, so asking the
-  arguments made the branch unreachable.
-- **Row 6 says when a corpus measures no element class at all.** On N200 the
-  build proposes 0 plans and exits 2 before the accounting door, so 16 549
-  elements land as unaccounted with no declared fate — a finding about the run
-  that read as a finding about the build.
-
-## [0.10.1] — 2026-09-18
-
-### Added
-
 - **`okf build --accounting PATH`: content accounting per element.** Before
   extraction, every source document is inventoried in a per-format element
   vocabulary: headings, paragraphs, tables, cells, images, and so on. After
@@ -241,6 +210,31 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- **The content-accounting gate: a document refused whole is never clean.**
+  Its elements are all booked as coded rejections, so u = 0 and d = 0, and
+  `refused_whole` asks its question only for a corpus that persisted NOTHING —
+  one refused source beside an accepted one read as clean with the content
+  gone. `Unit.refused` is that loss with its own column and the document's code
+  in the note.
+- **The STS JSON role map reads the publisher's own tags.** `count_sts_json`
+  compared the raw tag string where the XML witness has always used `_local`,
+  so `mml:math` reached `tag == "math"` on nothing — 74 formulas in N200
+  Vegbygging:2024 counted as 0. And the publisher's JSON writes a figure's
+  caption as `figcaption` under the `graphic`, not as the `fig/caption`
+  NISO-STS writes — 430 of them over the eight deliveries measured. No other
+  count moves, measured role by role over those eight and the committed twins.
+- **The mutation harness is a gate.** A surviving mutant now exits 1; the run
+  ended `2 if errors else 0`, so `killed 0 of 1` exited 0. PM's X2 mutant — a
+  report may declare a document rejected while the bundle holds it — is in the
+  set and is killed by a new test driven from both sides.
+- **The skipped-row guard measures the machine, not the argument.** Row 6 is
+  SKIPPED exactly when the corpora the arguments name are absent, so asking the
+  arguments made the branch unreachable.
+- **Row 6 says when a corpus measures no element class at all.** On N200 the
+  build proposes 0 plans and exits 2 before the accounting door, so 16 549
+  elements land as unaccounted with no declared fate — a finding about the run
+  that read as a finding about the build.
+
 - **An inline PDF image gets a stable name (0.10.1).** pdfminer names an
   inline image (`BI … EI`) from `id()` of a Python object, so a pointer line
   changed between two runs of one build and two concept files of the reference