Harden conversation replies and prioritize newest candidates

tests/repository-account-isolation.test.ts

@@ -121,13 +121,26 @@ describe('account-bound domain repositories', () => {
     expect(claims.getClaim('room', 'event')).toEqual({
       conversationId: 'room', incomingKey: 'event', status: 'pending',
       replyText: 'durable reply', incomingAt: 50, claimedAt: 60,
-      lastAttemptAt: 70, attemptCount: 1, sentAt: null,
+      lastAttemptAt: 70, attemptCount: 1, sentAt: null, supersededAt: null,
     });
     expect(claims.listPending()).toEqual([expect.objectContaining({ incomingKey: 'event' })]);
     expect(claims.releasePending('room', 'event')).toBe(true);
     expect(claims.listPending()).toEqual([]);
   });
 
+  it('keeps superseded reply claims as an auditable terminal record', () => {
+    const claims = new ConversationAutomationClaimRepository(db, ACCOUNT_A);
+    expect(claims.tryClaim('room', 'stale-event', 'stale reply', 50, 60)).toBe(true);
+
+    expect(claims.markSuperseded('room', 'stale-event', 80)).toBe(true);
+    expect(claims.getClaim('room', 'stale-event')).toMatchObject({
+      status: 'superseded',
+      supersededAt: 80,
+      sentAt: null,
+    });
+    expect(claims.listPending()).toEqual([]);
+  });
+
   it('claims recipients globally and blocks usernames with existing chat history', () => {
     db.prepare(`
       INSERT INTO reddit_conversations (