diff --git a/apps/api/src/workers/aider_event_processor.py b/apps/api/src/workers/aider_event_processor.py
new file mode 100644
index 00000000..dd828f3d
--- /dev/null
+++ b/apps/api/src/workers/aider_event_processor.py
@@ -0,0 +1,198 @@
+# aider_event_processor_job | 2026-04-20 @ Asia/Taipei
+"""aider-watch 事件處理器
+
+消費 Redis stream `signals:aider:events` (由 /api/v1/aider/events webhook 推入)：
+1. 解析 AiderEventIn
+2. 若應該觸發 incident → build_signal_data → IncidentEngine.process_signal
+3. 寫入 aider_events 表（含 incident_id 關聯）
+4. XACK
+
+仿 workers/signal_worker.py，但簡化（無 Active Sweeper）。
+
+@author Claude Code
+@date 2026-04-20
+"""
+from __future__ import annotations
+import asyncio
+import os
+import socket
+from typing import Any
+
+import structlog
+
+from src.core.redis_client import get_redis, get_worker_redis
+from src.db.base import get_session_factory
+from src.models.aider import AiderEventIn
+from src.repositories.aider_event_repository import AiderEventRepository
+from src.services.aider_event_service import build_signal_data, should_create_incident
+from src.services.incident_engine import get_incident_engine
+
+logger = structlog.get_logger(__name__)
+
+# =========================================================================
+# Constants
+# =========================================================================
+
+STREAM_KEY_DEFAULT = "signals:aider:events"
+CONSUMER_GROUP = "aider_processors"
+CONSUMER_NAME = f"aider_{socket.gethostname()}"
+BATCH_SIZE = 10
+BLOCK_MS = 5000
+GRACEFUL_SHUTDOWN_TIMEOUT_S = 30
+
+
+def _stream_key() -> str:
+    """取得 Redis stream key，可覆蓋環境變數。"""
+    return os.environ.get("AIDER_EVENTS_STREAM_KEY", STREAM_KEY_DEFAULT)
+
+
+# =========================================================================
+# Processor
+# =========================================================================
+
+class AiderEventProcessor:
+    """Redis Streams consumer for aider events."""
+
+    def __init__(self) -> None:
+        self._running = False
+        self._task: asyncio.Task | None = None
+
+    async def _ensure_consumer_group(self) -> None:
+        """確保 Consumer Group 存在。"""
+        r = get_redis()
+        try:
+            await r.xgroup_create(_stream_key(), CONSUMER_GROUP,
+                                   id="0", mkstream=True)
+            logger.info("aider_consumer_group_created",
+                        stream=_stream_key(), group=CONSUMER_GROUP)
+        except Exception as e:
+            if "BUSYGROUP" in str(e):
+                logger.debug("aider_consumer_group_exists", group=CONSUMER_GROUP)
+            else:
+                raise
+
+    async def start(self) -> None:
+        """啟動消費循環。"""
+        if self._running:
+            logger.warning("aider_processor_already_running")
+            return
+        await self._ensure_consumer_group()
+        self._running = True
+        self._task = asyncio.create_task(self._consume_loop())
+        logger.info("aider_processor_started",
+                    stream=_stream_key(), group=CONSUMER_GROUP, consumer=CONSUMER_NAME)
+
+    async def stop(self) -> None:
+        """優雅關閉。"""
+        if not self._running:
+            return
+        self._running = False
+        if self._task:
+            try:
+                await asyncio.wait_for(self._task, timeout=GRACEFUL_SHUTDOWN_TIMEOUT_S)
+            except TimeoutError:
+                self._task.cancel()
+            except asyncio.CancelledError:
+                pass
+        logger.info("aider_processor_stopped")
+
+    async def _consume_loop(self) -> None:
+        """主消費循環。"""
+        r = get_worker_redis()
+        stream_key = _stream_key()
+        while self._running:
+            try:
+                messages = await r.xreadgroup(
+                    groupname=CONSUMER_GROUP, consumername=CONSUMER_NAME,
+                    streams={stream_key: ">"},
+                    count=BATCH_SIZE, block=BLOCK_MS,
+                )
+                if not messages:
+                    continue
+                for _stream_name, entries in messages:
+                    for message_id, data in entries:
+                        await self._process_one(stream_key, message_id, data)
+            except asyncio.CancelledError:
+                break
+            except Exception as e:
+                logger.exception("aider_processor_loop_error", error=str(e))
+                await asyncio.sleep(1.0)
+
+    async def _process_one(self, stream_key: str, msg_id: Any, data: dict) -> None:
+        """處理單筆 message：parse → (maybe) incident → DB write → ACK。"""
+        try:
+            raw = data.get(b"payload") or data.get("payload")
+            if isinstance(raw, bytes):
+                raw = raw.decode()
+            ev = AiderEventIn.model_validate_json(raw)
+        except Exception:
+            logger.exception("aider_processor_parse_failed", msg_id=msg_id)
+            # Parse 失敗不重試（bad payload），直接 ACK 避免卡 pending
+            await self._ack(stream_key, msg_id)
+            return
+
+        incident_id: str | None = None
+        if should_create_incident(ev):
+            try:
+                sig_data = build_signal_data(ev)
+                if sig_data is not None:
+                    engine = get_incident_engine()
+                    incident = await engine.process_signal(sig_data)
+                    if incident:
+                        incident_id = getattr(incident, "incident_id", None)
+            except Exception:
+                logger.exception("aider_processor_incident_failed",
+                                  session_id=ev.session_id, type=ev.type)
+                # 不中斷 — 即使 incident 失敗，event 仍要持久化
+
+        try:
+            session_factory = get_session_factory()
+            async with session_factory() as session:
+                repo = AiderEventRepository(session)
+                await repo.insert(
+                    session_id=ev.session_id, ts=ev.ts, type_=ev.type,
+                    host=ev.host, payload=ev.payload, incident_id=incident_id,
+                )
+                await session.commit()
+        except Exception:
+            logger.exception("aider_processor_db_write_failed",
+                              session_id=ev.session_id)
+            # DB 失敗就不 ACK，靠 Redis pending list 保留重試
+            return
+
+        await self._ack(stream_key, msg_id)
+
+    async def _ack(self, stream_key: str, msg_id: Any) -> None:
+        """確認訊息已處理。"""
+        try:
+            r = get_worker_redis()
+            await r.xack(stream_key, CONSUMER_GROUP, msg_id)
+        except Exception:
+            logger.exception("aider_processor_ack_failed", msg_id=msg_id)
+
+
+# =========================================================================
+# Lifespan entry (called from main.py in Task A9)
+# =========================================================================
+
+_instance: AiderEventProcessor | None = None
+
+
+def get_aider_event_processor() -> AiderEventProcessor:
+    """取得 AiderEventProcessor singleton。"""
+    global _instance
+    if _instance is None:
+        _instance = AiderEventProcessor()
+    return _instance
+
+
+async def run_aider_event_processor_loop() -> None:
+    """main.py lifespan 呼叫此函式。"""
+    proc = get_aider_event_processor()
+    await proc.start()
+    try:
+        while proc._running:
+            await asyncio.sleep(60)
+    except asyncio.CancelledError:
+        await proc.stop()
+        raise
diff --git a/apps/api/tests/test_aider_event_processor.py b/apps/api/tests/test_aider_event_processor.py
new file mode 100644
index 00000000..675e65cc
--- /dev/null
+++ b/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