fix: back off after Reddit access denials

tests/reddit-api.test.ts

@@ -490,7 +490,7 @@ describe('RedditApiClient', () => {
       expect(result).toEqual([]);
     });
 
-    it('returns empty array for 403 private subreddit', async () => {
+    it('returns empty array and explains an initial 403 access denial', async () => {
       const error = { isAxiosError: true, response: { status: 403 } };
       const mockAxios = { get: vi.fn().mockRejectedValue(error) };
       vi.mocked(axios.create).mockReturnValue(mockAxios as any);
@@ -498,6 +498,23 @@ describe('RedditApiClient', () => {
       const client2 = new RedditApiClient(getTestConfig(), logger);
       const result = await client2.getNewPosts('private');
       expect(result).toEqual([]);
+      expect(logger.logs).toContainEqual(expect.objectContaining({
+        level: 'warn', message: expect.stringContaining('HTTP 403'),
+      }));
+    });
+
+    it('treats consecutive 403 listing responses as a temporary Reddit block', async () => {
+      const error = { isAxiosError: true, response: { status: 403 } };
+      const mockAxios = { get: vi.fn().mockRejectedValue(error) };
+      vi.mocked(axios.create).mockReturnValue(mockAxios as unknown as AxiosInstance);
+      const scheduler: RedditRequestScheduler = { schedule: async (request) => await request(), extendCooldown: vi.fn() };
+      const client2 = new RedditApiClient(getTestConfig(), logger, scheduler);
+
+      await expect(client2.getNewPosts('first')).resolves.toEqual([]);
+      await expect(client2.getNewPosts('second')).rejects.toMatchObject({
+        name: 'RedditRateLimitError', retryAfterMs: 120_000,
+      });
+      expect(scheduler.extendCooldown).toHaveBeenCalledWith(120_000);
     });
 
     it('throws a compact error with the Reddit rate-limit reset delay on 429', async () => {