@@ -789,6 +789,7 @@ const SELF_TEST_BATTERIES = Object.freeze({
   '#18719: a RETRACTED claim leaves the pool — a withdrawn claim never governs': 36,
   '#18683: the card-comment read pages to a cap — past 100 is UNJUDGED, ⛔ never a truncated pool': 27,
   '#18764: a DECORATED claim ENTERS the pool — ONE reading, and it is the sibling\'s': 24,
+  '#18828: a SECOND `Claim:` by ONE seat — the writer-side prohibition, finally READ': 51,
 });
 
 // DELETING an entry silences that battery's floor exactly as effectively as
@@ -800,8 +801,9 @@ const SELF_TEST_BATTERIES = Object.freeze({
 // one #17915 adds, by the one #17959 adds, by the one #18042 adds, and by the
 // one #18174 adds, and by the one #18141 adds, and by the one #17919 adds, and
 // by the one #16833 adds, and by the one #18456 adds, and by the one #18719
-// adds, and by the one #18683 adds, and by the one #18764 adds.
-const SELF_TEST_BATTERY_FLOOR = 31;
+// adds, and by the one #18683 adds, and by the one #18764 adds, and by the one
+// #18828 adds.
+const SELF_TEST_BATTERY_FLOOR = 32;
 
 // The key an assertion is filed under when no battery is open. It is not a
 // declared battery, so it reds by the same set difference rather than silently
@@ -8482,6 +8484,154 @@ export async function selfTest() {
   t('⭐ the RETRACTION path still reads the sigil-led #18373 line — narrowing it to the shared reading would unland #18719', claimRetractions(RTX_18373).has(RTX_18373.find((r) => r.id === RTX_WITHDRAWN)));
   t('⭐ …while the SHARED reading does not strip a leading sigil, so the two paths are ⛔ NOT interchangeable', markerMatches(CLAIM_COMMENT_MARKER, '🚨 Claim: PM loop round 1') === false);
 
+  // -- #18828: a SECOND `Claim:` by ONE seat, NAMED -------------------------
+  //
+  // The rule is this file's own (#17366 block, upstairs): the claim protocol
+  // forbids a second `Claim:`. What the reader did with one was RANK it —
+  // `rejected: 1 … a SUPERSEDED claim`, exit 0 — so a writer-side prohibition
+  // had no enforcing reader, and the record used the word for a transition the
+  // protocol DESIGNED about a line it says must not be written.
+  //
+  // ⭐ The pins below are per DIRECTION, and each one carries its own
+  // non-vacuity control: an assertion that some thread is silent proves nothing
+  // unless the SAME thread, with one thing changed, is named.
+  battery('#18828: a SECOND `Claim:` by ONE seat — the writer-side prohibition, finally READ');
+  const R28 = (id, at, login, lines) => ({ id, created_at: at, user: { login }, body: [].concat(lines).join('\n') });
+  const R28_SEAT = 'os-support-ai';
+  const R28_CLAIM = (id, at, login, o = {}) =>
+    R28(id, at, login, [
+      `${o.marker ?? 'Claim:'} PM loop round ${o.round ?? 1}`,
+      `Session: \`session_01DvvamiacK328idtBYJBxV3\``,
+      o.branch === null ? 'Branch: named in the PR body' : `Branch: \`${o.branch ?? 'claude/issue-4242-first'}\``,
+      'Clause-②: no',
+    ]);
+  const R28_A = R28_CLAIM(7100000001, '2026-09-18T01:00:00Z', R28_SEAT);
+  const R28_B = R28_CLAIM(7100000002, '2026-09-18T02:00:00Z', R28_SEAT, { round: 2, branch: 'claude/issue-4242-second' });
+  const R28_PAIR = (rows) => ({ pr: 18999, card: 18828, draft: true, prLabels: [], cardLabels: [], cardComments: rows });
+  const R28_CODES = (rows) => pairRows(R28_PAIR(rows)).map((r) => r.code);
+  const R28_ROW = (rows) => pairRows(R28_PAIR(rows)).find((r) => r.code === 'C8')?.text ?? '';
+  const R28_FIELD = (rows, key) => [pairInputRecord(R28_PAIR(rows))[key]].flat().join('\n');
+  const R28_IDS = (rows) => claimRepeats(rows).map((g) => g.ids.join('+')).join(' | ');
+
+  // (a) the shape the card measured five times over.
+  t('⭐ (a) two LIVE claims by ONE seat, no retraction between them — ONE named group carrying BOTH ids', R28_IDS([R28_A, R28_B]) === '7100000001+7100000002', R28_IDS([R28_A, R28_B]));
+  t('…and `--pair` earns a C8 FINDING, which is its exit 4', R28_CODES([R28_A, R28_B]).includes('C8'), R28_CODES([R28_A, R28_B]).join());
+  t('⛔ …a VERDICT and never a NOTE: the code lives in `pairRows`, and `pairNotes` does not carry it', pairNotes(R28_PAIR([R28_A, R28_B])).every((n) => n.code !== 'C8') && EXIT_PAIR_ADVERSE === 4 && EXIT_PAIR_ADVERSE !== EXIT_OK);
+  t('…the ROW names the author and BOTH comment ids', says(R28_ROW([R28_A, R28_B]), R28_SEAT) && says(R28_ROW([R28_A, R28_B]), '7100000001') && says(R28_ROW([R28_A, R28_B]), '7100000002'));
+  t('…and it names BOTH sanctioned repairs — the correction key and the `Release:`', says(R28_ROW([R28_A, R28_B]), 'Clause-②-correction') && says(R28_ROW([R28_A, R28_B]), '`Release:`'));
+  t('…and the input record READS the same two ids, beside the carrier it selected', says(R28_FIELD([R28_A, R28_B], 'claim.repeat'), '7100000001') && says(R28_FIELD([R28_A, R28_B], 'claim.repeat'), '7100000002'));
+  t('⛔ CONTROL: ONE claim by that same seat is silent — no group, no row, and the record says so', R28_IDS([R28_A]) === '' && !R28_CODES([R28_A]).includes('C8') && says(R28_FIELD([R28_A], 'claim.repeat'), 'none — no author holds'));
+  t('⛔ CONTROL: the SELECTOR did not move — the newest still governs and the older is still listed SUPERSEDED', claimCarrierSelection([R28_A, R28_B]).pool.map((r) => r.id).join() === '7100000002' && says(R28_FIELD([R28_A, R28_B], 'claim.rejected'), 'a SUPERSEDED claim'));
+  t('⛔ …and the refusal is an ADDITIONAL reading, ⛔ not a new selector: same pool, same rejected count as before', claimCarrierSelection([R28_A, R28_B]).rejected.length === 1 && claimCarrierSelection([R28_A, R28_B]).claims.length === 2 && CLAIM_SELECTION_RULE.includes('the GOVERNING claim'));
+
+  // (b) the p1 shape — REPORTED in the filing round, ⛔ not refused here.
+  const R28_OTHER = R28_CLAIM(7100000003, '2026-09-18T02:00:00Z', 'os-litant', { round: 2, branch: 'claude/issue-4242-second' });
+  t('⭐ (b) two live claims by DIFFERENT authors ⇒ ⛔ NOT this state — an ownership transfer is a separate reading', R28_IDS([R28_A, R28_OTHER]) === '' && !R28_CODES([R28_A, R28_OTHER]).includes('C8'));
+  t('…and that thread still reads exactly as it did: the newer governs, the older is SUPERSEDED, exit 0', claimCarrierSelection([R28_A, R28_OTHER]).pool.map((r) => r.id).join() === '7100000003' && says(R28_FIELD([R28_A, R28_OTHER], 'claim.rejected'), 'a SUPERSEDED claim'));
+  t('⛔ CONTROL: make those two authors ONE and the same thread is named — the author test is what decides', R28_IDS([R28_A, { ...R28_OTHER, user: { login: R28_SEAT } }]) === '7100000001+7100000003');
+  t('…and the rule PRINTED with the row says so in as many words, so a reader is not left to infer it', CLAIM_REPEAT_RULE.includes('DIFFERENT authors are not this state'));
+
+  // (c) MEMBERSHIP first — a re-claim after a release is the protocol working.
+  const R28_RELEASE = R28(7100000010, '2026-09-18T01:30:00Z', R28_SEAT, 'Release: session `session_01DvvamiacK328idtBYJBxV3`, cause: 本卡改派, 去向: `pm:queue`');
+  const R28_NAMED_RETRACTION = R28(7100000011, '2026-09-18T01:30:00Z', R28_SEAT, '撤回本席的认领 `7100000001` —— 本卡改派');
+  t('⭐ (c) a fresh claim AFTER a `Release:` of the first ⇒ silent — a retracted claim does not stand', R28_IDS([R28_A, R28_RELEASE, R28_B]) === '' && !R28_CODES([R28_A, R28_RELEASE, R28_B]).includes('C8'));
+  t('…and the first is still listed RETRACTED, with the 「⛔ NOT superseded」 wording byte-unchanged', says(R28_FIELD([R28_A, R28_RELEASE, R28_B], 'claim.rejected'), 'RETRACTED') && says(R28_FIELD([R28_A, R28_RELEASE, R28_B], 'claim.rejected'), '⛔ NOT superseded: a withdrawn claim is not a candidate for governance at all, whatever its date'));
+  t('…and the id-naming retraction channel reads the same way — ⛔ not a `Release:`-only rule', R28_IDS([R28_A, R28_NAMED_RETRACTION, R28_B]) === '');
+  t('⛔ CONTROL: drop the retraction and those same two claims are named — the release is what clears it', R28_IDS([R28_A, R28_B]) === '7100000001+7100000002');
+  t('⭐ the repair is PERFORMABLE after the fact: `Release:` then ONE fresh claim leaves exactly one standing', R28_IDS([R28_A, R28_B, R28(7100000012, '2026-09-18T03:00:00Z', R28_SEAT, 'Release: session `x`, cause: 修复本席的双认领, 去向: `pm:queue`'), R28_CLAIM(7100000013, '2026-09-18T04:00:00Z', R28_SEAT, { round: 3 })]) === '');
+
+  // (d) the sanctioned exit stays the sanctioned exit.
+  const R28_CORRECTION = R28(7100000020, '2026-09-18T02:00:00Z', R28_SEAT, [
+    'Clause-②-correction: 7100000001',
+    'Clause-②: no',
+    'Session: `session_01DvvamiacK328idtBYJBxV3`',
+  ]);
+  t('⭐ (d) a `Clause-②-correction:` as the LATER row is not a claim — silent, and the pool never saw it', R28_IDS([R28_A, R28_CORRECTION]) === '' && !R28_CODES([R28_A, R28_CORRECTION]).includes('C8') && markerMatches(CLAIM_COMMENT_MARKER, R28_CORRECTION.body) === false);
+  t('…and the #17366 exit still WORKS: the declaration is read off the correction, untouched by this row', cardDeclaration([R28_A, R28_CORRECTION]).state === 'declared' && cardDeclaration([R28_A, R28_CORRECTION]).correctionNote !== undefined);
+  t('⛔ CONTROL: write that same correction as a SECOND `Claim:` instead and it is named — which is the whole card', R28_IDS([R28_A, R28_B]) !== '' && says(R28_ROW([R28_A, R28_B]), 'never enters the pool'));
+
+  // (e) ONE reading of the marker, and it is the sibling's (#18764).
+  const R28_BOLD = R28_CLAIM(7100000030, '2026-09-18T02:00:00Z', R28_SEAT, { marker: '**Claim:**', round: 2 });
+  const R28_TICK = R28_CLAIM(7100000031, '2026-09-18T02:00:00Z', R28_SEAT, { marker: '`Claim:`', round: 2 });
+  t('⭐ (e) a DECORATED second claim (`**Claim:**`) is counted exactly as a bare one', R28_IDS([R28_A, R28_BOLD]) === '7100000001+7100000030');
+  t('…and the backticked spelling with it', R28_IDS([R28_A, R28_TICK]) === '7100000001+7100000031');
+  t('⛔ CONTROL: the raw constant REFUSES both bodies — the counting is the sibling\'s ONE reading, ⛔ not a second reader here', CLAIM_COMMENT_MARKER.test(R28_BOLD.body) === false && CLAIM_COMMENT_MARKER.test(R28_TICK.body) === false && markerMatches(CLAIM_COMMENT_MARKER, R28_BOLD.body) === true);
+  t('⛔ CONTROL: a markdown LIST ITEM is not a claim, so it is not a SECOND one either — the refusals are the sibling\'s', R28_IDS([R28_A, R28(7100000032, '2026-09-18T02:00:00Z', R28_SEAT, '- Claim: PM loop round 2\nBranch: `claude/issue-4242-second`')]) === '');
+
+  // (f) the prohibition is on the WRITING, ⛔ not on the parse.
+  const R28_UNPARSED = R28_CLAIM(7100000040, '2026-09-18T02:00:00Z', R28_SEAT, { round: 2, branch: null });
+  t('⭐ (f) a second claim whose `Branch:` parses to ZERO branches is still a second claim', R28_IDS([R28_A, R28_UNPARSED]) === '7100000001+7100000040');
+  t('…and it is named even though governance itself is unresolvable on that thread', cardDeclaration([R28_A, R28_UNPARSED]).state === 'claim-branch-unparsed' && R28_CODES([R28_A, R28_UNPARSED]).includes('C8'));
+  t('⛔ CONTROL: give that same row a parseable branch and the two are named just the same — the parse fires nothing', R28_IDS([R28_A, { ...R28_UNPARSED, body: R28_B.body }]) === '7100000001+7100000040');
+
+  // (g) one refusal per seat, ⛔ never one per pair.
+  const R28_C = R28_CLAIM(7100000050, '2026-09-18T03:00:00Z', R28_SEAT, { round: 3, branch: 'claude/issue-4242-third' });
+  t('⭐ (g) THREE claims by one seat ⇒ ONE refusal naming all three', claimRepeats([R28_A, R28_B, R28_C]).length === 1 && R28_IDS([R28_A, R28_B, R28_C]) === '7100000001+7100000002+7100000050');
+  t('…and exactly ONE C8 row on the pair — ⛔ not one per ordered pair, which would have been three', R28_CODES([R28_A, R28_B, R28_C]).filter((c) => c === 'C8').length === 1);
+  t('…with all three ids in the sentence a reader is handed', says(R28_ROW([R28_A, R28_B, R28_C]), '7100000001') && says(R28_ROW([R28_A, R28_B, R28_C]), '7100000002') && says(R28_ROW([R28_A, R28_B, R28_C]), '7100000050'));
+  t('⛔ CONTROL: retract two of the three and one standing claim is left — silent', R28_IDS([R28_A, R28_B, R28(7100000051, '2026-09-18T02:30:00Z', R28_SEAT, 'Release: session `x`, cause: y, 去向: `pm:queue`'), R28_C]) === '');
+
+  // (h) fail closed on an unattributable row — the way `claimRetractions` does.
+  const R28_NO_USER = { id: 7100000060, created_at: '2026-09-18T02:00:00Z', body: R28_B.body };
+  t('⭐ (h) an unattributable LATER row is never counted — ⛔ `null` is a refusal, never a wildcard', R28_IDS([R28_A, R28_NO_USER]) === '' && !R28_CODES([R28_A, R28_NO_USER]).includes('C8'));
+  t('…and an unattributable FIRST row is not counted either — both sides fail closed', R28_IDS([{ id: 7100000061, created_at: '2026-09-18T01:00:00Z', body: R28_A.body }, R28_B]) === '');
+  t('…and the direction is STATED in the rule the row prints, so silence here is readable rather than inferred', CLAIM_REPEAT_RULE.includes('unattributable row is never counted'));
+  t('⛔ CONTROL: give that same row a login and it is named — the attribution is what was missing', R28_IDS([R28_A, { ...R28_NO_USER, user: { login: R28_SEAT } }]) === '7100000001+7100000060');
+
+  // (i) the seat's own shape: a later comment that QUOTES or DISCUSSES the word.
+  const R28_QUOTE = R28(7100000070, '2026-09-18T02:00:00Z', R28_SEAT, [
+    '⚠️ 本席上一条 `Claim:` 的申报行写错了,已另发 `Clause-②-correction:` 更正,⛔ 未再发一条认领。',
+    '      "question": "the governing-claim instrument reads a second Claim: as a SUPERSESSION",',
+  ]);
+  const R28_ROUND_REPORT = R28(7100000071, '2026-09-18T03:00:00Z', R28_SEAT, [
+    '## 轮次报告 — `domain:cli` 执行 PM 席',
+    '- 本轮认领 3 张卡;每张 Claim: 行均由本席发出。',
+  ]);
+  t('⭐ (i) a later same-author comment that QUOTES the word is not a claim — the marker is read at LINE START', R28_IDS([R28_A, R28_QUOTE]) === '' && !R28_CODES([R28_A, R28_QUOTE]).includes('C8'));
+  t('…and a round report mentioning the word mid-line is not one either', R28_IDS([R28_A, R28_ROUND_REPORT]) === '');
+  t('…both of them together with the claim still leave exactly one standing claim on the thread', claimCarrierSelection([R28_A, R28_QUOTE, R28_ROUND_REPORT]).live.length === 1);
+  t('⛔ CONTROL: move that same word to the OPENING of a line and it IS a second claim', R28_IDS([R28_A, R28(7100000072, '2026-09-18T02:00:00Z', R28_SEAT, 'Claim: 本席重新认领\nBranch: `claude/issue-4242-second`')]) === '7100000001+7100000072');
+
+  // The unread and empty halves — ⛔ never a clean reading.
+  t('⛔ an UNREAD thread names nobody and reads nothing', claimRepeats(null).length === 0 && c8SecondClaimSameSeat({ pr: 1, card: 2, cardComments: null }) === null);
+  t('…and the record SAYS unread rather than reporting a clean thread', says(R28_FIELD(null, 'claim.repeat'), 'UNREAD'));
+  t('⛔ an EMPTY thread is silent, and says the other sentence', claimRepeats([]).length === 0 && says(R28_FIELD([], 'claim.repeat'), 'none — no author holds'));
+
+  // ⭐ The LIVE census, replayed from the real rows the filing card named.
+  // Population: both boards this gate reads, at 2026-09-18T00:05Z — 533 open
+  // cards in `objectstack-ai/objectstack`, 416 in `objectstack-ai/objectui`,
+  // 167 of them carrying at least one claim comment. The five below are the
+  // measured instances on the objectstack board, all by one seat; #18559 is the
+  // same seat on the same shift doing it the sanctioned way.
+  const R28_LIVE = (id, at, head) => R28(id, at, R28_SEAT, [
+    head,
+    '',
+    'Claim: session `session_01DvvamiacK328idtBYJBxV3`',
+    'Branch: `claude/issue-18540-actions-native-error-leak`',
+    'Clause-②: no',
+  ]);
+  const R28_LIVE_CARDS = [
+    [18540, R28_LIVE(5719079496, '2026-09-17T18:09:58Z', '## 认领 — `domain:cli` 执行 PM 席'), R28_LIVE(5720020876, '2026-09-17T19:28:06Z', '## 认领(补正,取代 `5719079496` 的申报行)— `domain:cli` 执行 PM 席')],
+    [18677, R28_LIVE(5720104138, '2026-09-17T19:34:43Z', '## 认领'), R28_LIVE(5720190458, '2026-09-17T19:42:03Z', '## 认领(补正)')],
+    [18748, R28_LIVE(5720212595, '2026-09-17T19:43:49Z', '## 认领'), R28_LIVE(5720888122, '2026-09-17T20:36:49Z', '## 认领(补正)')],
+    [18651, R28_LIVE(5721424769, '2026-09-17T21:23:22Z', '## 认领'), R28_LIVE(5721997887, '2026-09-17T22:20:07Z', '## 认领(补正)')],
+    [18778, R28_LIVE(5721425530, '2026-09-17T21:23:25Z', '## 认领'), R28_LIVE(5722028692, '2026-09-17T22:23:32Z', '## 认领(补正)')],
+  ];
+  t('⭐ the five measured instances (2026-09-18T00:05Z) are ALL named — ⛔ five green readings before this row', R28_LIVE_CARDS.every(([, a, b]) => claimRepeats([a, b]).length === 1));
+  t('…each naming its own two comment ids and the one seat that wrote them', R28_LIVE_CARDS.every(([, a, b]) => R28_IDS([a, b]) === `${a.id}+${b.id}` && claimRepeats([a, b])[0].author === R28_SEAT), R28_LIVE_CARDS.map(([n, a, b]) => `${n}:${R28_IDS([a, b])}`).join(' '));
+  t('⛔ …and every one of them read GREEN before, as a SUPERSESSION — the measurement this row answers', R28_LIVE_CARDS.every(([, a, b]) => says(R28_FIELD([a, b], 'claim.rejected'), 'a SUPERSEDED claim')));
+  t('⛔ CONTROL #18559 — the same seat, same shift, the SANCTIONED shape: one claim plus a correction ⇒ silent', (() => {
+    const claim = R28_LIVE(5721425131, '2026-09-17T21:23:24Z', '## 认领 — `domain:cli` 执行 PM 席 #6024');
+    const correction = R28(5721779100, '2026-09-17T21:57:34Z', R28_SEAT, ['Clause-②-correction: 5721425131', 'Clause-②: no', 'Session: `session_01DvvamiacK328idtBYJBxV3`']);
+    return claimRepeats([claim, correction]).length === 0 && !R28_CODES([claim, correction]).includes('C8');
+  })());
+  t('⭐ …and that control IS the repair this row prints, which is why the row prints it', says(R28_ROW([R28_A, R28_B]), 'Clause-②-correction: <claim comment id>'));
+
+  // ONE derivation — the record and the verdict cannot disagree.
+  t('the repeat field is DECLARED in the pair roster, so it renders on every block, filled or not', INPUT_RECORD_PAIR_FIELDS.includes('claim.repeat'));
+  t('⭐ ONE derivation: the ids the ROW names are the ids the RECORD names', claimRepeats([R28_A, R28_B])[0].ids.every((id) => says(R28_ROW([R28_A, R28_B]), id) && says(R28_FIELD([R28_A, R28_B], 'claim.repeat'), id)));
+  t('⛔ the row is not in the sweep\'s NOTE family and the record carries no verdict word for it', !says(R28_FIELD([R28_A, R28_B], 'claim.repeat'), 'exit 4') && says(R28_FIELD([R28_A, R28_B], 'claim.repeat'), 'row C8 is the verdict'));
+
   // -- The floor: every declared battery RAN, and ran its cases (#13489) -----
   //
   // Evaluated after every battery has had its chance and BEFORE the verdict, so
@@ -8552,7 +8702,9 @@ export async function selfTest() {
       + 'and on a refusal — with the selected carrier, its body fingerprint and the rejected '
       + 'candidates each stated, the DECORATED claim that enters the pool and governs through '
       + 'the sibling\'s one reading — the constant unwidened, and the file\'s two undecoration '
-      + 'paths pinned as the two jobs they are — and the exit register).',
+      + 'paths pinned as the two jobs they are, the SECOND `Claim:` by one seat named as the state '
+      + 'the protocol forbids writing rather than ranked as a supersession — per direction, with a '
+      + 'non-vacuity control each and the five measured instances replayed — and the exit register).',
   );
 
   selfTestReachedVerdict = true;