fix(video-render): F6 ReliableQueue 적용 (F6 part 4)

- worker.py: poll_once + ReliableQueue + startup recovery
- 4 provider (sora/veo/kling/seedance) dispatch table 보존
- Dockerfile: build context=services/, _shared 포함, PYTHONPATH=/app
- docker-compose.yml: video-render build context 갱신

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

services/video-render/tests/test_worker.py

@@ -41,3 +41,56 @@ def test_dispatch_unknown_job_type_logs_error():
         args = m.call_args[0]
         assert args[0] == "t5"
         assert args[1] == "failed"
+
+
+# ----- F6: ReliableQueue poll_once -----
+
+import json
+from unittest.mock import AsyncMock, MagicMock
+
+
+@pytest.mark.asyncio
+async def test_poll_once_acks_on_success(monkeypatch):
+    payload = {"task_id": "t1", "job_type": "sora_generation", "params": {}}
+    raw = json.dumps(payload).encode()
+    fake_queue = AsyncMock()
+    fake_queue.dequeue = AsyncMock(return_value=(payload, raw))
+    fake_queue.ack = AsyncMock()
+    fake_queue.fail = AsyncMock()
+    monkeypatch.setattr(worker, "_dispatch", MagicMock())
+    handled = await worker.poll_once(fake_queue)
+    assert handled is True
+    fake_queue.ack.assert_awaited_once_with(raw)
+    fake_queue.fail.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_poll_once_calls_fail_on_dispatch_exception(monkeypatch):
+    payload = {"task_id": "t2", "job_type": "sora_generation", "params": {}}
+    raw = json.dumps(payload).encode()
+    fake_queue = AsyncMock()
+    fake_queue.dequeue = AsyncMock(return_value=(payload, raw))
+    fake_queue.ack = AsyncMock()
+    fake_queue.fail = AsyncMock()
+
+    def _boom(p):
+        raise RuntimeError("dispatch crash")
+
+    monkeypatch.setattr(worker, "_dispatch", _boom)
+    handled = await worker.poll_once(fake_queue)
+    assert handled is True
+    fake_queue.fail.assert_awaited_once_with(raw, payload)
+    fake_queue.ack.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_poll_once_returns_false_on_timeout(monkeypatch):
+    fake_queue = AsyncMock()
+    fake_queue.dequeue = AsyncMock(return_value=None)
+    fake_queue.ack = AsyncMock()
+    fake_queue.fail = AsyncMock()
+    monkeypatch.setattr(worker, "_dispatch", MagicMock())
+    handled = await worker.poll_once(fake_queue)
+    assert handled is False
+    fake_queue.ack.assert_not_awaited()
+    fake_queue.fail.assert_not_awaited()