feat(worker): AiderEventProcessor — Redis stream consumer + incident + DB write

- Implement Task A7: background worker consuming signals:aider:events stream
- Parse AiderEventIn from Redis XREADGROUP messages
- Call IncidentEngine.process_signal for incident-worthy events
- Persist aider_events to PostgreSQL with optional incident_id FK
- XACK on success, preserve in pending list on DB failure (retry)
- ACK on parse failure (bad JSON avoids pending list jam)
- Match signal_worker.py pattern: no Active Sweeper (MVP)
- Unit tests: 4 tests covering incident creation, non-incident events, malformed payloads, engine failures

Tests: 37 passed (4 new + 33 existing regression)

apps/api/tests/test_aider_event_processor.py

@@ -0,0 +1,163 @@
+# test_aider_event_processor | 2026-04-20 @ Asia/Taipei
+"""Unit tests for AiderEventProcessor."""
+import pytest
+import json
+from datetime import datetime, timezone, timedelta
+from unittest.mock import AsyncMock, MagicMock, patch
+from src.workers.aider_event_processor import AiderEventProcessor
+
+
+TAIPEI = timezone(timedelta(hours=8))
+
+
+def _payload_dict():
+    """基本的 aider event payload。"""
+    return {
+        "ts": datetime.now(TAIPEI).isoformat(),
+        "session_id": "s1", "host": "ogt-mac",
+        "type": "error",
+        "payload": {"cwd": "/r", "model": "elephant-alpha",
+                    "kind": "api_rate_limit", "message": "429",
+                    "context_50chars": ""},
+    }
+
+
+@pytest.mark.asyncio
+async def test_process_one_error_event_creates_incident_and_writes_db(monkeypatch):
+    """error event 應建 incident + 寫 DB。"""
+    # Mock incident engine
+    fake_incident = MagicMock()
+    fake_incident.incident_id = "inc-123"
+    fake_engine = MagicMock()
+    fake_engine.process_signal = AsyncMock(return_value=fake_incident)
+    monkeypatch.setattr("src.workers.aider_event_processor.get_incident_engine",
+                        lambda: fake_engine)
+
+    # Mock DB session factory + repo
+    inserted = {}
+    class FakeRepo:
+        def __init__(self, sess): pass
+        async def insert(self, **kw): inserted.update(kw); return 1
+    class FakeSession:
+        async def __aenter__(self): return self
+        async def __aexit__(self, *a): return False
+        async def commit(self): pass
+    monkeypatch.setattr("src.workers.aider_event_processor.AiderEventRepository",
+                        FakeRepo)
+    monkeypatch.setattr("src.workers.aider_event_processor.get_session_factory",
+                        lambda: (lambda: FakeSession()))
+
+    # Mock redis ack
+    fake_r = MagicMock()
+    fake_r.xack = AsyncMock()
+    monkeypatch.setattr("src.workers.aider_event_processor.get_worker_redis",
+                        lambda: fake_r)
+
+    # Act
+    proc = AiderEventProcessor()
+    payload = _payload_dict()
+    data = {b"payload": json.dumps(payload).encode()}
+    await proc._process_one("stream", "1-0", data)
+
+    # Assert
+    assert fake_engine.process_signal.called
+    assert inserted.get("incident_id") == "inc-123"
+    assert inserted.get("type_") == "error"
+    fake_r.xack.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_process_one_session_start_no_incident(monkeypatch):
+    """session_start 不應建 incident，但應寫 DB。"""
+    fake_engine = MagicMock()
+    fake_engine.process_signal = AsyncMock()
+    monkeypatch.setattr("src.workers.aider_event_processor.get_incident_engine",
+                        lambda: fake_engine)
+
+    inserted = {}
+    class FakeRepo:
+        def __init__(self, sess): pass
+        async def insert(self, **kw): inserted.update(kw); return 1
+    class FakeSession:
+        async def __aenter__(self): return self
+        async def __aexit__(self, *a): return False
+        async def commit(self): pass
+    monkeypatch.setattr("src.workers.aider_event_processor.AiderEventRepository",
+                        FakeRepo)
+    monkeypatch.setattr("src.workers.aider_event_processor.get_session_factory",
+                        lambda: (lambda: FakeSession()))
+
+    fake_r = MagicMock()
+    fake_r.xack = AsyncMock()
+    monkeypatch.setattr("src.workers.aider_event_processor.get_worker_redis",
+                        lambda: fake_r)
+
+    # Act
+    proc = AiderEventProcessor()
+    payload = _payload_dict()
+    payload["type"] = "session_start"
+    payload["payload"] = {"cwd": "/r", "model": "m", "aider_args": [],
+                          "aider_pid": 1, "cli_version": "0"}
+    data = {b"payload": json.dumps(payload).encode()}
+    await proc._process_one("stream", "1-0", data)
+
+    # Assert
+    assert not fake_engine.process_signal.called  # session_start 不建 incident
+    assert inserted.get("incident_id") is None    # DB 依然寫入
+    assert inserted.get("type_") == "session_start"
+    fake_r.xack.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_process_one_malformed_payload_acks_and_skips(monkeypatch, caplog):
+    """malformed JSON 應 ACK 避免卡 pending，但不建 DB record。"""
+    fake_r = MagicMock()
+    fake_r.xack = AsyncMock()
+    monkeypatch.setattr("src.workers.aider_event_processor.get_worker_redis",
+                        lambda: fake_r)
+
+    # Act
+    proc = AiderEventProcessor()
+    data = {b"payload": b"this is not json"}
+    await proc._process_one("stream", "1-0", data)
+
+    # Assert
+    fake_r.xack.assert_called_once()  # 壞 payload ACK 避免卡 pending
+
+
+@pytest.mark.asyncio
+async def test_incident_failure_still_writes_db(monkeypatch):
+    """incident engine 壞掉時，event 仍要進 DB（不丟資料）。"""
+    fake_engine = MagicMock()
+    fake_engine.process_signal = AsyncMock(side_effect=RuntimeError("engine down"))
+    monkeypatch.setattr("src.workers.aider_event_processor.get_incident_engine",
+                        lambda: fake_engine)
+
+    inserted = {}
+    class FakeRepo:
+        def __init__(self, sess): pass
+        async def insert(self, **kw): inserted.update(kw); return 1
+    class FakeSession:
+        async def __aenter__(self): return self
+        async def __aexit__(self, *a): return False
+        async def commit(self): pass
+    monkeypatch.setattr("src.workers.aider_event_processor.AiderEventRepository",
+                        FakeRepo)
+    monkeypatch.setattr("src.workers.aider_event_processor.get_session_factory",
+                        lambda: (lambda: FakeSession()))
+
+    fake_r = MagicMock()
+    fake_r.xack = AsyncMock()
+    monkeypatch.setattr("src.workers.aider_event_processor.get_worker_redis",
+                        lambda: fake_r)
+
+    # Act
+    proc = AiderEventProcessor()
+    payload = _payload_dict()
+    data = {b"payload": json.dumps(payload).encode()}
+    await proc._process_one("stream", "1-0", data)
+
+    # Assert
+    assert inserted.get("type_") == "error"
+    assert inserted.get("incident_id") is None  # engine 壞，無 id
+    fake_r.xack.assert_called_once()            # 仍 ACK