Prioritize growth retries and randomize intake

tests/account-growth.test.ts

@@ -295,6 +295,36 @@ describe('AccountGrowthService', () => {
       expect(outcome).toMatchObject({ kind: 'idle' });
       expect(h.postComment).not.toHaveBeenCalled();
     });
+
+    it('waits for a queued retry instead of discovering another thread', async () => {
+      h.repo.enqueueDiscovered(ACCOUNT, [thread('retry')], NOW);
+      h.repo.claimNext(ACCOUNT, `growth:${ACCOUNT}`, 60_000, NOW);
+      h.repo.defer(
+        ACCOUNT,
+        'retry',
+        `growth:${ACCOUNT}`,
+        'Temporary generation failure',
+        NOW + 15 * 60_000,
+        NOW,
+      );
+
+      const outcome = await h.service.tick({ allowPosting: true });
+
+      expect(outcome).toEqual({
+        kind: 'idle',
+        reason: 'Existing growth queue is waiting for its retry time',
+      });
+      expect(h.getHotPosts).not.toHaveBeenCalled();
+      expect(h.repo.listRecent(ACCOUNT)).toHaveLength(1);
+    });
+
+    it('queues only one thread so each new comment rerolls the subreddit', async () => {
+      h.getHotPosts.mockResolvedValue([thread('a'), thread('b'), thread('c')]);
+
+      await h.service.tick({ allowPosting: true });
+
+      expect(h.repo.listRecent(ACCOUNT)).toHaveLength(1);
+    });
   });
 
   describe('posting', () => {