diff --git a/scripts/check-kko-provenance.mjs b/scripts/check-kko-provenance.mjs
index a5098cd..e5c2b58 100644
--- a/scripts/check-kko-provenance.mjs
+++ b/scripts/check-kko-provenance.mjs
@@ -13,9 +13,14 @@
  * ── What it enforces ─────────────────────────────────────────────────────────────────
  *   1. `ontology/kko/kko-2.10.n3` still hashes to the sha256 recorded in PROVENANCE.md, and is
  *      still the recorded byte length. The doc is the source of the expectation, so the doc and
- *      the artifact can never silently disagree.
+ *      the artifact can never silently disagree. **SHA-256:** and **Bytes:** are both REQUIRED
+ *      fields: a record that omits or mangles one FAILS this gate. It does not skip the
+ *      comparison and report success — see the note above the byte check for why that distinction
+ *      is the whole point of the script.
  *   2. PROVENANCE.md pins a COMMIT, not just a branch. `@ master` is a moving reference: re-run
  *      the retrieval later and you may get different bytes while claiming the same provenance.
+ *      The pin is recognised by its label — ``commit `<40-hex>` `` — not by "some 40-hex run
+ *      appears somewhere in the document".
  *   3. The generated `ts/src/kko-data.ts` is exactly what `scripts/gen-kko.mjs` produces from
  *      that .n3 — i.e. the ontology the engine actually SHIPS derives from the vendored source.
  *      A hand-edit to kko-data.ts, or a re-vendored .n3 without a regeneration, otherwise leaves
@@ -50,21 +55,45 @@ if (actual !== declared)
       `  This digest is pinned by consumers too (prophet-platform apps/owl-reasoner asserts it at import).\n` +
       `  Re-vendor, then update PROVENANCE.md AND every consumer pin in the same change.`)
 
-const declaredBytes = Number(((doc.match(/\*\*Bytes:\*\*\s*([\d,]+)/) || [])[1] || '0').replace(/,/g, ''))
-if (declaredBytes && bytes.length !== declaredBytes)
+// The byte count is a REQUIRED field and the comparison below is UNCONDITIONAL.
+// This used to read `Number(… || '0')` guarded by `if (declaredBytes && …)`. A missing or
+// unparseable **Bytes:** therefore became 0, `if (0 && …)` never fired, and the byte check
+// silently evaporated — while the run still printed
+//     ✓ KKO provenance verified — d907919fb40f20ed… (327,797 bytes)
+// quoting the file's OWN length as though it had been checked against the record. A check that
+// disappears when its input goes missing is worse than no check at all: it manufactures the
+// evidence that it ran. Absent or malformed input must FAIL, exactly the way the missing
+// **SHA-256:** case above already fails. (Same disease as the commit-pin note below.)
+const declaredBytesText = (doc.match(/\*\*Bytes:\*\*\s*([0-9][0-9,]*)/) || [])[1]
+const declaredBytes = declaredBytesText === undefined ? NaN : Number(declaredBytesText.replace(/,/g, ''))
+if (!Number.isSafeInteger(declaredBytes))
+  die('ontology/kko/PROVENANCE.md does not declare a parseable **Bytes:** <count> — the record must state what the artifact should be')
+if (bytes.length !== declaredBytes)
   die(`vendored KKO TBox is ${bytes.length} bytes, PROVENANCE.md declares ${declaredBytes}`)
 
 // ── 2) the source must be PINNED, not a moving branch ref ──
-// NB: search for the commit pin only AFTER removing the sha256 from the text. A naive
-// /[0-9a-f]{40}/ over the whole document matches a 40-char window INSIDE the 64-char sha256 —
-// the check would have been satisfied by the very digest it is supposed to be independent of.
+// The pin is located by its LABEL — ``commit `<40-hex>` `` — not by scanning the document for a
+// bare 40-hex run. An unanchored scan does not answer "is the source pinned?", it answers "does
+// any 40-hex string appear anywhere in this file?", and those come apart: a sha1 of some other
+// artifact, another repo's commit sha, a hash sitting inside an unrelated URL, all satisfy it
+// while the source line still reads `@ master`. The check would pass by accident and report a pin
+// that is not there.
+// Two details are load-bearing:
+//   · the (?![0-9a-f]) tail — without it the pattern accepts the first 40 characters of a 64-char
+//     sha256 that happens to be labelled `commit`;
+//   · the digest strip below — so the artifact's own sha256 can never be the thing that supplies
+//     its own pin, even if this pattern is loosened later.
 // (A checker that validates itself validates nothing; this repo's estate has been bitten by
-// exactly that shape before.)
+// exactly that shape before — including by the byte check a few lines above, which until
+// 2026-07-30 switched ITSELF off whenever PROVENANCE.md stopped declaring a byte count, and went
+// on printing a success line that named the bytes it had not verified. Absent input must fail,
+// never skip.)
 const withoutDigest = doc.split(declared).join('')
-const commitPin = (withoutDigest.match(/\b([0-9a-f]{40})\b/) || [])[1]
+const commitPin = (withoutDigest.match(/\b[Cc]ommit\s+`?([0-9a-f]{40})(?![0-9a-f])/) || [])[1]
 if (!commitPin)
   die('ontology/kko/PROVENANCE.md pins no commit sha. "@ master" is a MOVING reference — the same ' +
-      'retrieval later can return different bytes and still claim this provenance. Pin the commit.')
+      'retrieval later can return different bytes and still claim this provenance. ' +
+      'Pin the commit, and record it in the form: commit `<40-hex-sha>`')
 for (const needle of ['SocioProphet/kbpedia', 'CC-BY-4.0'])
   if (!doc.includes(needle)) die(`ontology/kko/PROVENANCE.md does not record ${needle}`)
 
diff --git a/ts/src/kko-provenance-guard.test.ts b/ts/src/kko-provenance-guard.test.ts
new file mode 100644
index 0000000..609aa56
--- /dev/null
+++ b/ts/src/kko-provenance-guard.test.ts
@@ -0,0 +1,123 @@
+/**
+ * Regression tests for `scripts/check-kko-provenance.mjs` — the gate itself, not the ontology.
+ *
+ * Why these exist: the byte-count check in that script used to read
+ *     const declaredBytes = Number((doc.match(/\*\*Bytes:\*\*\s*([\d,]+)/) || [])[1] || '0')
+ *     if (declaredBytes && bytes.length !== declaredBytes) die(...)
+ * so a PROVENANCE.md with no parseable **Bytes:** produced 0, `if (0 && …)` never fired, and the
+ * comparison silently evaporated — while the run still printed a success line quoting the file's
+ * OWN byte count as though it had been verified against the record. The gate reported that it had
+ * checked something it had not checked.
+ *
+ * A test suite for a gate has to prove teeth in BOTH directions: that the real record still
+ * passes, and that each specific corruption still fails. Asserting only the happy path is how a
+ * check that cannot fail gets to look healthy forever.
+ *
+ * These drive the REAL script as a subprocess rather than re-declaring its regexes here — a test
+ * that re-implements the thing it is testing agrees with itself by construction and proves
+ * nothing. The script resolves every path relative to its own file URL, so each case runs in a
+ * throwaway root: a copy of the script, a copy of the record under test, and symlinks back to the
+ * real .n3 and ts/ tree. The repo's own ontology/kko/PROVENANCE.md is never written to.
+ */
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import { spawnSync } from 'node:child_process'
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const here = path.dirname(fileURLToPath(import.meta.url))
+const repo = path.resolve(here, '..', '..')
+const guardName = 'check-kko-provenance.mjs'
+const guardPath = path.join(repo, 'scripts', guardName)
+const recordPath = path.join(repo, 'ontology', 'kko', 'PROVENANCE.md')
+const n3Path = path.join(repo, 'ontology', 'kko', 'kko-2.10.n3')
+
+/** Run the guard against a rewritten record. Returns its exit code and combined output. */
+const runGuard = (mutate: (doc: string) => string): { code: number; out: string } => {
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), 'hg-kko-guard-'))
+  try {
+    fs.mkdirSync(path.join(root, 'scripts'))
+    fs.mkdirSync(path.join(root, 'ontology', 'kko'), { recursive: true })
+    fs.copyFileSync(guardPath, path.join(root, 'scripts', guardName))
+    fs.symlinkSync(n3Path, path.join(root, 'ontology', 'kko', 'kko-2.10.n3'))
+    fs.symlinkSync(path.join(repo, 'ts'), path.join(root, 'ts'))
+    fs.writeFileSync(
+      path.join(root, 'ontology', 'kko', 'PROVENANCE.md'),
+      mutate(fs.readFileSync(recordPath, 'utf-8')),
+    )
+    const r = spawnSync(process.execPath, ['--import', 'tsx', path.join(root, 'scripts', guardName)], {
+      cwd: repo, // so `--import tsx` resolves from the repo's node_modules
+      encoding: 'utf-8',
+    })
+    return { code: r.status ?? -1, out: `${r.stdout ?? ''}${r.stderr ?? ''}` }
+  } finally {
+    fs.rmSync(root, { recursive: true, force: true })
+  }
+}
+
+/**
+ * String surgery that must actually bite. If PROVENANCE.md is reworded so a needle stops
+ * matching, the mutation would no-op and the case would "pass" by testing an unmodified
+ * document — the same silently-skipped-check failure this file exists to prevent.
+ */
+const rewrite = (doc: string, from: string, to: string): string => {
+  assert.ok(doc.includes(from), `test fixture is stale: PROVENANCE.md no longer contains ${JSON.stringify(from)}`)
+  return doc.split(from).join(to)
+}
+
+const BYTES_LINE = '**Bytes:** 327,797'
+const PIN_LINE = '@ commit `3f888b397255b69d1439fd95823e97011ed9440b` (branch `master`)'
+const PIN_URL = '/SocioProphet/kbpedia/3f888b397255b69d1439fd95823e97011ed9440b/'
+const OTHER_SHA256 = '0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef'
+const OTHER_SHA1 = 'aaaaaaaabbbbbbbbccccccccddddddddeeeeeeee'
+
+// ─── control: the gate must still accept the real record ──────────────────────────
+// A checker that has been "hardened" into rejecting the genuine artifact is worse than the bug.
+test('the committed PROVENANCE.md passes the guard unchanged', () => {
+  const { code, out } = runGuard((d) => d)
+  assert.equal(code, 0, out)
+  assert.match(out, /✓ KKO provenance verified/)
+})
+
+// ─── the byte count is required, and the comparison is unconditional ──────────────
+test('a PROVENANCE.md with no **Bytes:** line FAILS (it must not skip the byte check)', () => {
+  const { code, out } = runGuard((d) => rewrite(d, `${BYTES_LINE}\n`, ''))
+  assert.equal(code, 1, `expected the guard to fail, got:\n${out}`)
+  assert.match(out, /does not declare a parseable \*\*Bytes:\*\*/)
+  // The old code printed the success line here, quoting the file's own length as verified.
+  assert.doesNotMatch(out, /provenance verified/)
+})
+
+test('a malformed **Bytes:** FAILS rather than defaulting to 0', () => {
+  const { code, out } = runGuard((d) => rewrite(d, BYTES_LINE, '**Bytes:** abc'))
+  assert.equal(code, 1, `expected the guard to fail, got:\n${out}`)
+  assert.match(out, /does not declare a parseable \*\*Bytes:\*\*/)
+  assert.doesNotMatch(out, /provenance verified/)
+})
+
+test('a **Bytes:** that disagrees with the artifact FAILS', () => {
+  const { code, out } = runGuard((d) => rewrite(d, BYTES_LINE, '**Bytes:** 999,999'))
+  assert.equal(code, 1, `expected the guard to fail, got:\n${out}`)
+  assert.match(out, /is 327797 bytes, PROVENANCE\.md declares 999999/)
+})
+
+// ─── the commit pin is found by its label, not by "some 40-hex run exists" ────────
+test('an unpinned source FAILS even when an unrelated 40-hex sha appears in the record', () => {
+  const { code, out } = runGuard((d) => {
+    let s = rewrite(d, PIN_LINE, '@ `master`')
+    s = rewrite(s, PIN_URL, '/SocioProphet/kbpedia/master/')
+    return rewrite(s, '## What it is', `**Consumer pin landed in commit** \`${OTHER_SHA1}\`.\n\n## What it is`)
+  })
+  assert.equal(code, 1, `expected the guard to fail, got:\n${out}`)
+  assert.match(out, /pins no commit sha/)
+})
+
+test('a second sha256 recorded alongside the genuine pin does not break the pin check', () => {
+  const { code, out } = runGuard((d) =>
+    rewrite(d, '## What it is', `**Consumer copy SHA-256:** \`${OTHER_SHA256}\`\n\n## What it is`),
+  )
+  assert.equal(code, 0, out)
+  assert.match(out, /✓ KKO provenance verified/)
+})