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 () => {

tests/reddit-request-coordinator.test.ts

@@ -55,4 +55,18 @@ describe('RedditRequestCoordinator', () => {
     await second;
     expect(sleeps).toEqual([16_000]);
   });
+
+  it('paces a queued request after a failed attempt without an explicit cooldown', async () => {
+    let now = 0;
+    const sleeps: number[] = [];
+    const coordinator = new RedditRequestCoordinator(6_500, {
+      now: () => now,
+      sleep: async (ms) => { sleeps.push(ms); now += ms; },
+    });
+
+    await expect(coordinator.schedule(async () => { throw new Error('403'); })).rejects.toThrow('403');
+    await coordinator.schedule(async () => undefined);
+
+    expect(sleeps).toEqual([6_500]);
+  });
 });