diff --git a/src/db/repositories.ts b/src/db/repositories.ts
index a95f404cb4..4715da2fbb 100644
--- a/src/db/repositories.ts
+++ b/src/db/repositories.ts
@@ -430,6 +430,11 @@ export async function upsertPullRequestFromGitHub(
       headShaObservedAt,
       lastSeenOpenAt,
       payloadJson: jsonString(payload),
+      // GitHub's own PR creation time (see PullRequestRecord.createdAt's doc comment, src/types.ts) --
+      // set ONLY here, on first insert, and deliberately absent from onConflictDoUpdate's `set` below so
+      // a resync never overwrites it. `?? undefined` falls through to the column's own $defaultFn when a
+      // sparse payload omits created_at, matching every other optional GitHub-sourced field's convention.
+      createdAt: pr.created_at ?? undefined,
       updatedAt: syncedAt,
     })
     .onConflictDoUpdate({
@@ -4254,15 +4259,25 @@ export async function markUnseenOpenPullRequestsClosed(env: Env, fullName: strin
   return Number(result.meta.changes ?? 0);
 }
 
+// Ordered by DESCENDING PR number so a repo with >500 PRs keeps its MOST RECENT ones, not an arbitrary/
+// unordered slice a plain LIMIT would otherwise return (Postgres gives no ordering guarantee without
+// ORDER BY -- confirmed live: an unordered 500-row cap on a 2930-row repo produced a skewed, non-
+// representative sample that inverted src/services/outcome-calibration.ts's slop-band merge-rate check,
+// which reads this exact function, and fired a false "score not discriminating" ops_anomaly). Every other
+// caller (MCP tools, gate-precision, quality metrics, recap) benefits the same way: recent PRs are the
+// relevant population for almost every one of them, an arbitrary old slice never was.
 export async function listPullRequests(env: Env, fullName: string): Promise<PullRequestRecord[]> {
   const db = getDb(env.DB);
-  const rows = await db.select().from(pullRequests).where(eq(pullRequests.repoFullName, fullName)).limit(500);
+  const rows = await db.select().from(pullRequests).where(eq(pullRequests.repoFullName, fullName)).orderBy(desc(pullRequests.number)).limit(500);
   return rows.map(toPullRequestRecordFromRow);
 }
 
+// Same ordering rationale as listPullRequests above, but cross-repo -- PR number resets per repo, so
+// createdAt (an ISO 8601 UTC string, sortable lexicographically) is the only field that's globally
+// comparable for "most recent" across every repo at once.
 export async function listAllPullRequests(env: Env): Promise<PullRequestRecord[]> {
   const db = getDb(env.DB);
-  const rows = await db.select().from(pullRequests).limit(2000);
+  const rows = await db.select().from(pullRequests).orderBy(desc(pullRequests.createdAt)).limit(2000);
   return rows.map(toPullRequestRecordFromRow);
 }
 
diff --git a/test/unit/db-parsers.test.ts b/test/unit/db-parsers.test.ts
index 551ec2cbcb..f5eb4453b3 100644
--- a/test/unit/db-parsers.test.ts
+++ b/test/unit/db-parsers.test.ts
@@ -17,6 +17,7 @@ import {
   getLatestScoringModelSnapshot,
   getFreshOfficialMinerDetection,
   getPullRequest,
+  listAllPullRequests,
   listPullRequests,
   listPullRequestDetailSyncStates,
   listRepoSyncSegments,
@@ -1336,3 +1337,51 @@ describe("database row parser hardening", () => {
     expect(JSON.parse(raw?.snapshot_json ?? "{}")).toMatchObject({ githubId: "", githubUsername: "", issueLabels: [] });
   });
 });
+
+// #ops-anomaly-calibration-sample-order: both list functions cap their row count, and a LIMIT with no ORDER BY
+// gives no ordering guarantee -- confirmed live on a 2930-row repo, where the resulting arbitrary 500-row slice
+// inverted src/services/outcome-calibration.ts's slop-band merge-rate comparison (which reads listPullRequests)
+// and fired a false ops_anomaly "score not discriminating" alert, even though the score discriminates correctly
+// (monotonically decreasing merge rate by rising severity) over the true full population. Ordering by recency
+// fixes this at the source, for every caller, not just calibration.
+describe("listPullRequests / listAllPullRequests ordering (#ops-anomaly-calibration-sample-order)", () => {
+  it("listPullRequests returns a repo's PRs ordered by DESCENDING number, regardless of insert order", async () => {
+    const env = createTestEnv();
+    for (const number of [3, 1, 4, 2]) {
+      await upsertPullRequestFromGitHub(env, "owner/repo", {
+        number,
+        title: `PR #${number}`,
+        state: "open",
+        user: { login: "contributor1" },
+        labels: [],
+        body: null,
+      });
+    }
+
+    const numbers = (await listPullRequests(env, "owner/repo")).map((pr) => pr.number);
+    expect(numbers).toEqual([4, 3, 2, 1]);
+  });
+
+  it("listAllPullRequests returns PRs ordered by DESCENDING createdAt across repos, regardless of insert order", async () => {
+    const env = createTestEnv();
+    const seeds: Array<{ repoFullName: string; number: number; createdAt: string }> = [
+      { repoFullName: "owner/repo-a", number: 1, createdAt: "2026-01-01T00:00:00.000Z" },
+      { repoFullName: "owner/repo-b", number: 1, createdAt: "2026-03-01T00:00:00.000Z" },
+      { repoFullName: "owner/repo-a", number: 2, createdAt: "2026-02-01T00:00:00.000Z" },
+    ];
+    for (const seed of seeds) {
+      await upsertPullRequestFromGitHub(env, seed.repoFullName, {
+        number: seed.number,
+        title: `${seed.repoFullName}#${seed.number}`,
+        state: "open",
+        user: { login: "contributor1" },
+        labels: [],
+        body: null,
+        created_at: seed.createdAt,
+      });
+    }
+
+    const ordered = (await listAllPullRequests(env)).map((pr) => `${pr.repoFullName}#${pr.number}`);
+    expect(ordered).toEqual(["owner/repo-b#1", "owner/repo-a#2", "owner/repo-a#1"]);
+  });
+});