diff --git a/packages/gittensory-engine/src/duplicate-winner.ts b/packages/gittensory-engine/src/duplicate-winner.ts
new file mode 100644
index 0000000000..48bfaa689e
--- /dev/null
+++ b/packages/gittensory-engine/src/duplicate-winner.ts
@@ -0,0 +1,111 @@
+/**
+ * Duplicate-winner adjudication (#dup-winner). Flag-gated by GITTENSORY_DUPLICATE_WINNER.
+ *
+ * When several OPEN PRs link the same issue (a duplicate cluster), the legacy behavior gate-blocks +
+ * auto-closes EVERY sibling as a duplicate — no winner survives. With the flag ON, exactly ONE winner is
+ * spared: the earliest claimant. Sparse legacy rows that do not yet have claim timing fail closed so unknown
+ * ordering cannot arbitrarily suppress duplicate evidence. Only the LOSERS are blocked/closed; the winner
+ * still must pass CI / conflict / gate / linked-issue / slop on its OWN merits.
+ *
+ * This module is PURE — no IO, no Date, no random — so the same inputs always yield the same verdict and the
+ * caller can compute the winner ONCE per review run and thread the result boolean consistently into every
+ * surface (advisory finding, close reason, slop, panels), so they agree by construction.
+ *
+ * ELECTION ORDER (#dup-winner true-creation-time): prefer each PR's true GitHub `pull_request.created_at` —
+ * the real order contributors opened their PRs in — over `linkedIssueClaimedAt` (gittensory's own sync-time,
+ * i.e. whenever a webhook/sweep/backfill pass happened to OBSERVE the linked issue). Sync order and creation
+ * order diverge whenever processing isn't strictly FIFO (a stalled sweep catching up on a backlog, backfill
+ * reordering, webhook delivery delay), under the old claim-time-only rule, that divergence could crown a
+ * LATER contributor the winner and close the PR of whoever actually opened first. `createdAt` is compared
+ * only when BOTH sides of a given comparison have a valid one; otherwise this falls back to the legacy
+ * claim-time comparison unchanged, so sparse/legacy rows keep their existing fail-closed behavior exactly.
+ *
+ * INVARIANT (the caller MUST honor it): {@link openSiblingNumbers} carries OPEN-only sibling PR numbers. The
+ * existing sources already exclude closed/merged PRs. Once the winner closes (e.g. red CI), it leaves the open
+ * set and the next-earliest OPEN claimant becomes the winner on re-eval — no permanently-orphaned cluster.
+ *
+ * SECOND CONSUMER (#2278): this module is intentionally engine-hosted (not `src/`-only) because its election
+ * logic is reusable for the miner's own soft-claim adjudication — deciding which of several miners claiming
+ * the same issue proceeds. A future contributor wiring the miner's local claim ledger should import this
+ * module rather than reimplementing the election rule, so both the maintainer gate and the miner agree on
+ * exactly one winner by construction.
+ */
+
+export type DuplicateClaimMember = {
+  number: number;
+  linkedIssueClaimedAt?: string | null | undefined;
+  /** GitHub's true PR creation time. See the module doc's "ELECTION ORDER" note. */
+  createdAt?: string | null | undefined;
+};
+
+/**
+ * True iff `prNumber` is the cluster winner: the minimum of `{prNumber} ∪ openSiblingNumbers`. An empty
+ * sibling list ⇒ the PR is alone in (or out of) the cluster ⇒ winner. A sibling list that happens to contain
+ * `prNumber` itself is harmless — the comparison is still min-based.
+ *
+ * @deprecated Use {@link isDuplicateClusterWinnerByClaim}. PR-number election is retained only for legacy
+ * compatibility callers that do not have claim timestamps.
+ */
+export function isDuplicateClusterWinner(prNumber: number, openSiblingNumbers: number[]): boolean {
+  for (const sibling of openSiblingNumbers) {
+    if (sibling < prNumber) return false;
+  }
+  return true;
+}
+
+/**
+ * True iff `pr` is the earliest-elected claimant in the open duplicate cluster (see the module doc's
+ * "ELECTION ORDER" note for the createdAt-vs-claim-time precedence). Sparse legacy rows fail closed; ties
+ * between equally-ordered members use PR number.
+ */
+export function isDuplicateClusterWinnerByClaim(pr: DuplicateClaimMember, openSiblings: DuplicateClaimMember[]): boolean {
+  if (openSiblings.length === 0) return true;
+  for (const sibling of openSiblings) {
+    if (!prPrecedesSibling(pr, sibling)) return false;
+  }
+  return true;
+}
+
+/**
+ * True iff `pr` is ordered at or ahead of `sibling` for cluster-winner purposes. Prefers `createdAt` when BOTH
+ * sides have a valid one (the true creation-time order); otherwise falls back to the legacy `linkedIssueClaimedAt`
+ * comparison unchanged (including its fail-closed-on-missing/invalid-timestamp behavior), so a mixed
+ * legacy/modern cluster never silently guesses using two different clocks for the two sides of one comparison.
+ */
+function prPrecedesSibling(pr: DuplicateClaimMember, sibling: DuplicateClaimMember): boolean {
+  const prCreated = claimTimeMs(pr.createdAt);
+  const siblingCreated = claimTimeMs(sibling.createdAt);
+  if (prCreated !== null && siblingCreated !== null) {
+    if (prCreated !== siblingCreated) return prCreated < siblingCreated;
+    return pr.number <= sibling.number;
+  }
+  const prClaim = claimTimeMs(pr.linkedIssueClaimedAt);
+  if (prClaim === null) return false;
+  const siblingClaim = claimTimeMs(sibling.linkedIssueClaimedAt);
+  if (siblingClaim === null) return false;
+  if (siblingClaim < prClaim) return false;
+  if (siblingClaim === prClaim && sibling.number < pr.number) return false;
+  return true;
+}
+
+/**
+ * The winning PR number among `pr` and its open duplicate siblings, or `null` when the election is not
+ * determinable (mirrors {@link isDuplicateClusterWinnerByClaim}'s fail-closed semantics — this never guesses a
+ * specific winner when the ordering data is too sparse/ambiguous to be sure). Used only for DISPLAY (naming the
+ * winner in a loser's close comment, #dup-winner-credit) — the close/hold decision for any given PR is still
+ * driven directly by {@link isDuplicateClusterWinnerByClaim}, not by this function's return value.
+ */
+export function resolveDuplicateClusterWinnerNumber(pr: DuplicateClaimMember, openSiblings: DuplicateClaimMember[]): number | null {
+  if (isDuplicateClusterWinnerByClaim(pr, openSiblings)) return pr.number;
+  for (const sibling of openSiblings) {
+    const rest = openSiblings.filter((other) => other.number !== sibling.number);
+    if (isDuplicateClusterWinnerByClaim(sibling, [pr, ...rest])) return sibling.number;
+  }
+  return null;
+}
+
+function claimTimeMs(value: string | null | undefined): number | null {
+  if (!value) return null;
+  const parsed = Date.parse(value);
+  return Number.isFinite(parsed) ? parsed : null;
+}
diff --git a/packages/gittensory-engine/src/index.ts b/packages/gittensory-engine/src/index.ts
index 53513e7b95..47a63faf05 100644
--- a/packages/gittensory-engine/src/index.ts
+++ b/packages/gittensory-engine/src/index.ts
@@ -225,3 +225,9 @@ export { bestMetadataOpportunityAtOrAboveScore } from "./metadata-best-min-score
 export * as scoringModel from "./scoring/model.js";
 export * as scoringPreview from "./scoring/preview.js";
 export * as scoringPendingPrScenarios from "./scoring/pending-pr-scenarios.js";
+export {
+  isDuplicateClusterWinner,
+  isDuplicateClusterWinnerByClaim,
+  resolveDuplicateClusterWinnerNumber,
+  type DuplicateClaimMember,
+} from "./duplicate-winner.js";
diff --git a/packages/gittensory-engine/test/duplicate-winner.test.ts b/packages/gittensory-engine/test/duplicate-winner.test.ts
new file mode 100644
index 0000000000..522cc38d21
--- /dev/null
+++ b/packages/gittensory-engine/test/duplicate-winner.test.ts
@@ -0,0 +1,106 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import {
+  isDuplicateClusterWinner,
+  isDuplicateClusterWinnerByClaim,
+  resolveDuplicateClusterWinnerNumber,
+} from "../dist/index.js";
+
+test("barrel: the public entrypoint re-exports the duplicate-winner adjudication API", () => {
+  assert.equal(typeof isDuplicateClusterWinner, "function");
+  assert.equal(typeof isDuplicateClusterWinnerByClaim, "function");
+  assert.equal(typeof resolveDuplicateClusterWinnerNumber, "function");
+});
+
+test("isDuplicateClusterWinner: the lowest open sibling number wins", () => {
+  assert.equal(isDuplicateClusterWinner(5, [7, 9]), true);
+});
+
+test("isDuplicateClusterWinner: a lower open sibling beats this PR (loser)", () => {
+  assert.equal(isDuplicateClusterWinner(5, [3, 9]), false);
+});
+
+test("isDuplicateClusterWinner: an empty sibling list is always a winner", () => {
+  assert.equal(isDuplicateClusterWinner(5, []), true);
+});
+
+test("isDuplicateClusterWinnerByClaim: an empty sibling list is always a winner", () => {
+  assert.equal(isDuplicateClusterWinnerByClaim({ number: 5 }, []), true);
+});
+
+test("isDuplicateClusterWinnerByClaim: elects the earliest observed linked-issue claimant, not the lowest PR number", () => {
+  const earlier = { number: 9, linkedIssueClaimedAt: "2026-01-01T00:00:00Z" };
+  const later = { number: 3, linkedIssueClaimedAt: "2026-01-02T00:00:00Z" };
+  assert.equal(isDuplicateClusterWinnerByClaim(earlier, [later]), true);
+  assert.equal(isDuplicateClusterWinnerByClaim(later, [earlier]), false);
+});
+
+test("isDuplicateClusterWinnerByClaim: falls back to PR number for an equal known claim timestamp", () => {
+  const a = { number: 3, linkedIssueClaimedAt: "2026-01-01T00:00:00Z" };
+  const b = { number: 9, linkedIssueClaimedAt: "2026-01-01T00:00:00Z" };
+  assert.equal(isDuplicateClusterWinnerByClaim(a, [b]), true);
+  assert.equal(isDuplicateClusterWinnerByClaim(b, [a]), false);
+});
+
+test("isDuplicateClusterWinnerByClaim: fails closed when sparse legacy rows lack claim timestamps", () => {
+  assert.equal(isDuplicateClusterWinnerByClaim({ number: 5 }, [{ number: 9 }]), false);
+});
+
+test("isDuplicateClusterWinnerByClaim: fails closed on an invalid claim timestamp", () => {
+  assert.equal(
+    isDuplicateClusterWinnerByClaim({ number: 5, linkedIssueClaimedAt: "not-a-date" }, [{ number: 9, linkedIssueClaimedAt: "2026-01-01T00:00:00Z" }]),
+    false,
+  );
+});
+
+test("isDuplicateClusterWinnerByClaim createdAt precedence: elects the PR GitHub says opened first, even when observed later", () => {
+  const openedFirstButClaimedLater = {
+    number: 9,
+    createdAt: "2026-01-01T00:00:00Z",
+    linkedIssueClaimedAt: "2026-01-05T00:00:00Z",
+  };
+  const openedSecondButClaimedFirst = {
+    number: 3,
+    createdAt: "2026-01-02T00:00:00Z",
+    linkedIssueClaimedAt: "2026-01-01T00:00:00Z",
+  };
+  assert.equal(isDuplicateClusterWinnerByClaim(openedFirstButClaimedLater, [openedSecondButClaimedFirst]), true);
+  assert.equal(isDuplicateClusterWinnerByClaim(openedSecondButClaimedFirst, [openedFirstButClaimedLater]), false);
+});
+
+test("isDuplicateClusterWinnerByClaim createdAt precedence: falls back to claim-time when only one side has a valid createdAt", () => {
+  const modern = { number: 9, createdAt: "2026-01-01T00:00:00Z", linkedIssueClaimedAt: "2026-01-05T00:00:00Z" };
+  const legacy = { number: 3, linkedIssueClaimedAt: "2026-01-02T00:00:00Z" };
+  // Neither side has BOTH createdAt values, so this falls back to claim-time comparison: modern claimed later, so legacy wins.
+  assert.equal(isDuplicateClusterWinnerByClaim(legacy, [modern]), true);
+  assert.equal(isDuplicateClusterWinnerByClaim(modern, [legacy]), false);
+});
+
+test("isDuplicateClusterWinnerByClaim createdAt precedence: ties break by PR number", () => {
+  const a = { number: 3, createdAt: "2026-01-01T00:00:00Z" };
+  const b = { number: 9, createdAt: "2026-01-01T00:00:00Z" };
+  assert.equal(isDuplicateClusterWinnerByClaim(a, [b]), true);
+  assert.equal(isDuplicateClusterWinnerByClaim(b, [a]), false);
+});
+
+test("resolveDuplicateClusterWinnerNumber: returns this PR's own number when it is the winner", () => {
+  const pr = { number: 5, linkedIssueClaimedAt: "2026-01-01T00:00:00Z" };
+  const sibling = { number: 9, linkedIssueClaimedAt: "2026-01-02T00:00:00Z" };
+  assert.equal(resolveDuplicateClusterWinnerNumber(pr, [sibling]), 5);
+});
+
+test("resolveDuplicateClusterWinnerNumber: returns the actual winning sibling's number when this PR is a loser", () => {
+  const pr = { number: 9, linkedIssueClaimedAt: "2026-01-02T00:00:00Z" };
+  const sibling = { number: 5, linkedIssueClaimedAt: "2026-01-01T00:00:00Z" };
+  assert.equal(resolveDuplicateClusterWinnerNumber(pr, [sibling]), 5);
+});
+
+test("resolveDuplicateClusterWinnerNumber: an empty sibling list means this PR wins by default", () => {
+  assert.equal(resolveDuplicateClusterWinnerNumber({ number: 5 }, []), 5);
+});
+
+test("resolveDuplicateClusterWinnerNumber: returns null when the election is too ambiguous to name a specific winner", () => {
+  // Every member lacks a claim timestamp, so no one can be proven the winner (fails closed).
+  assert.equal(resolveDuplicateClusterWinnerNumber({ number: 5 }, [{ number: 9 }, { number: 3 }]), null);
+});
diff --git a/src/signals/duplicate-winner.ts b/src/signals/duplicate-winner.ts
index 9de8f9f496..c7980fe396 100644
--- a/src/signals/duplicate-winner.ts
+++ b/src/signals/duplicate-winner.ts
@@ -1,105 +1,15 @@
 /**
- * Duplicate-winner adjudication (#dup-winner). Flag-gated by GITTENSORY_DUPLICATE_WINNER.
- *
- * When several OPEN PRs link the same issue (a duplicate cluster), the legacy behavior gate-blocks +
- * auto-closes EVERY sibling as a duplicate — no winner survives. With the flag ON, exactly ONE winner is
- * spared: the earliest claimant. Sparse legacy rows that do not yet have claim timing fail closed so unknown
- * ordering cannot arbitrarily suppress duplicate evidence. Only the LOSERS are blocked/closed; the winner
- * still must pass CI / conflict / gate / linked-issue / slop on its OWN merits.
- *
- * This module is PURE — no IO, no Date, no random — so the same inputs always yield the same verdict and the
- * caller can compute the winner ONCE per review run and thread the result boolean consistently into every
- * surface (advisory finding, close reason, slop, panels), so they agree by construction.
- *
- * ELECTION ORDER (#dup-winner true-creation-time): prefer each PR's true GitHub `pull_request.created_at` —
- * the real order contributors opened their PRs in — over `linkedIssueClaimedAt` (gittensory's own sync-time,
- * i.e. whenever a webhook/sweep/backfill pass happened to OBSERVE the linked issue). Sync order and creation
- * order diverge whenever processing isn't strictly FIFO (a stalled sweep catching up on a backlog, backfill
- * reordering, webhook delivery delay), under the old claim-time-only rule, that divergence could crown a
- * LATER contributor the winner and close the PR of whoever actually opened first. `createdAt` is compared
- * only when BOTH sides of a given comparison have a valid one; otherwise this falls back to the legacy
- * claim-time comparison unchanged, so sparse/legacy rows keep their existing fail-closed behavior exactly.
- *
- * INVARIANT (the caller MUST honor it): {@link openSiblingNumbers} carries OPEN-only sibling PR numbers. The
- * existing sources already exclude closed/merged PRs. Once the winner closes (e.g. red CI), it leaves the open
- * set and the next-earliest OPEN claimant becomes the winner on re-eval — no permanently-orphaned cluster.
- */
-
-export type DuplicateClaimMember = {
-  number: number;
-  linkedIssueClaimedAt?: string | null | undefined;
-  /** GitHub's true PR creation time. See the module doc's "ELECTION ORDER" note. */
-  createdAt?: string | null | undefined;
-};
-
-/**
- * True iff `prNumber` is the cluster winner: the minimum of `{prNumber} ∪ openSiblingNumbers`. An empty
- * sibling list ⇒ the PR is alone in (or out of) the cluster ⇒ winner. A sibling list that happens to contain
- * `prNumber` itself is harmless — the comparison is still min-based.
- *
- * @deprecated Use {@link isDuplicateClusterWinnerByClaim}. PR-number election is retained only for legacy
- * compatibility callers that do not have claim timestamps.
- */
-export function isDuplicateClusterWinner(prNumber: number, openSiblingNumbers: number[]): boolean {
-  for (const sibling of openSiblingNumbers) {
-    if (sibling < prNumber) return false;
-  }
-  return true;
-}
-
-/**
- * True iff `pr` is the earliest-elected claimant in the open duplicate cluster (see the module doc's
- * "ELECTION ORDER" note for the createdAt-vs-claim-time precedence). Sparse legacy rows fail closed; ties
- * between equally-ordered members use PR number.
- */
-export function isDuplicateClusterWinnerByClaim(pr: DuplicateClaimMember, openSiblings: DuplicateClaimMember[]): boolean {
-  if (openSiblings.length === 0) return true;
-  for (const sibling of openSiblings) {
-    if (!prPrecedesSibling(pr, sibling)) return false;
-  }
-  return true;
-}
-
-/**
- * True iff `pr` is ordered at or ahead of `sibling` for cluster-winner purposes. Prefers `createdAt` when BOTH
- * sides have a valid one (the true creation-time order); otherwise falls back to the legacy `linkedIssueClaimedAt`
- * comparison unchanged (including its fail-closed-on-missing/invalid-timestamp behavior), so a mixed
- * legacy/modern cluster never silently guesses using two different clocks for the two sides of one comparison.
- */
-function prPrecedesSibling(pr: DuplicateClaimMember, sibling: DuplicateClaimMember): boolean {
-  const prCreated = claimTimeMs(pr.createdAt);
-  const siblingCreated = claimTimeMs(sibling.createdAt);
-  if (prCreated !== null && siblingCreated !== null) {
-    if (prCreated !== siblingCreated) return prCreated < siblingCreated;
-    return pr.number <= sibling.number;
-  }
-  const prClaim = claimTimeMs(pr.linkedIssueClaimedAt);
-  if (prClaim === null) return false;
-  const siblingClaim = claimTimeMs(sibling.linkedIssueClaimedAt);
-  if (siblingClaim === null) return false;
-  if (siblingClaim < prClaim) return false;
-  if (siblingClaim === prClaim && sibling.number < pr.number) return false;
-  return true;
-}
-
-/**
- * The winning PR number among `pr` and its open duplicate siblings, or `null` when the election is not
- * determinable (mirrors {@link isDuplicateClusterWinnerByClaim}'s fail-closed semantics — this never guesses a
- * specific winner when the ordering data is too sparse/ambiguous to be sure). Used only for DISPLAY (naming the
- * winner in a loser's close comment, #dup-winner-credit) — the close/hold decision for any given PR is still
- * driven directly by {@link isDuplicateClusterWinnerByClaim}, not by this function's return value.
- */
-export function resolveDuplicateClusterWinnerNumber(pr: DuplicateClaimMember, openSiblings: DuplicateClaimMember[]): number | null {
-  if (isDuplicateClusterWinnerByClaim(pr, openSiblings)) return pr.number;
-  for (const sibling of openSiblings) {
-    const rest = openSiblings.filter((other) => other.number !== sibling.number);
-    if (isDuplicateClusterWinnerByClaim(sibling, [pr, ...rest])) return sibling.number;
-  }
-  return null;
-}
-
-function claimTimeMs(value: string | null | undefined): number | null {
-  if (!value) return null;
-  const parsed = Date.parse(value);
-  return Number.isFinite(parsed) ? parsed : null;
-}
+ * Duplicate-winner adjudication (#dup-winner), extracted to `@jsonbored/gittensory-engine` (#2278) so the
+ * maintainer gate and the miner's own soft-claim adjudication (a later Phase-0 issue) import the identical,
+ * versioned election logic instead of drifting apart. See the engine module's doc comment for the full
+ * election-order rationale (createdAt-vs-claim-time precedence, fail-closed semantics).
+ *
+ * packages/gittensory-engine/src/duplicate-winner.ts (imported via relative source path, not the published
+ * module, matching the #2282 scoring-preview extraction) is the source of truth.
+ */
+export {
+  isDuplicateClusterWinner,
+  isDuplicateClusterWinnerByClaim,
+  resolveDuplicateClusterWinnerNumber,
+  type DuplicateClaimMember,
+} from "../../packages/gittensory-engine/src/duplicate-winner";