diff --git a/apps/api/src/services/aider_event_service.py b/apps/api/src/services/aider_event_service.py
new file mode 100644
index 00000000..e313d71c
--- /dev/null
+++ b/apps/api/src/services/aider_event_service.py
@@ -0,0 +1,111 @@
+# aider_event_service | 2026-04-20 @ Asia/Taipei
+"""aider event 分類 + 轉成 awoooi signal_data 給 IncidentService。
+
+設計原則：
+- 不重做 dedup — 既有 IncidentService.create_incident_from_signal 已有 3min fingerprint debounce
+- 不做 pattern extract — Task A8 ai_router 會直接從 aider_event_repository 聚合
+- 純函式為主，副作用（建 incident）由 caller（A7 processor job）管理
+"""
+from __future__ import annotations
+from typing import Any
+from src.models.aider import AiderEventIn
+from src.utils.secret_redactor import redact
+
+
+# ---- 分類 ----
+
+def classify_severity(ev: AiderEventIn) -> str | None:
+    """回傳對應 awoooi Signal 的 severity 字串（_parse_severity 會轉 P0-P3），
+    None = 不該建 incident。
+    映射：
+      error → warning (P2)
+      silent_timeout → info (P3)
+      session_end + nonzero exit + error_count>=3 → high (P1)
+      session_end + nonzero exit → warning (P2)
+      其他 → None
+    """
+    t = ev.type
+    if t == "error":
+        return "warning"
+    if t == "silent_timeout":
+        return "info"
+    if t == "session_end":
+        exit_code = ev.payload.get("exit_code", 0)
+        err_count = ev.payload.get("error_count", 0)
+        if exit_code != 0 and err_count >= 3:
+            return "high"
+        if exit_code != 0 or err_count >= 1:
+            return "warning"
+    return None
+
+
+def should_create_incident(ev: AiderEventIn) -> bool:
+    return classify_severity(ev) is not None
+
+
+# ---- signal_data 構造 ----
+
+def build_signal_data(ev: AiderEventIn) -> dict[str, Any] | None:
+    """把 AiderEventIn 轉成 IncidentService.create_incident_from_signal 所需 dict。
+    不該建 incident 的 event（session_start 等）回傳 None。
+
+    Fingerprint 設計：'aider:{session_id}:{type}' — 讓既有 3min debounce 自然發揮
+    （同 session 60s 內連續 5 個 error 會只建 1 個 incident）。
+    """
+    sev = classify_severity(ev)
+    if sev is None:
+        return None
+
+    p = redact(ev.payload)
+    cwd = p.get("cwd") or ""
+    model = p.get("model") or "unknown"
+    repo = _repo_basename(cwd)
+
+    alert_name_map = {
+        "error":          "AiderError",
+        "silent_timeout": "AiderSilentTimeout",
+        "session_end":    "AiderSessionFailure",
+    }
+    alert_name = alert_name_map.get(ev.type, "AiderEvent")
+
+    return {
+        "alert_name":  alert_name,
+        "severity":    sev,
+        "source":      "manual",                         # aider 不屬 prometheus/signoz/alertmanager/telegram
+        "fingerprint": f"aider:{ev.session_id}:{ev.type}",
+        "target":      repo or "unknown",
+        "labels": {
+            "session_id": ev.session_id,
+            "host":       ev.host,
+            "repo":       repo,
+            "model":      model,
+            "event_type": ev.type,
+        },
+        "annotations": {
+            "summary":     f"[aider/{ev.type}] {repo} ({model})",
+            "description": _compact_desc(ev.type, p),
+        },
+    }
+
+
+def _repo_basename(cwd: str) -> str:
+    """/Users/ogt/awoooi → awoooi"""
+    if not cwd:
+        return ""
+    return cwd.rstrip("/").rsplit("/", 1)[-1]
+
+
+def _compact_desc(event_type: str, payload: dict) -> str:
+    """把 payload 壓成 200 字內描述，secret 已 redacted。"""
+    if event_type == "error":
+        kind = payload.get("kind", "unknown")
+        msg = payload.get("message", "")[:150]
+        return f"kind={kind} message={msg}"
+    if event_type == "silent_timeout":
+        return f"idle_sec={payload.get('idle_sec')} tail={payload.get('last_output_tail','')[:50]}"
+    if event_type == "session_end":
+        return (f"exit_code={payload.get('exit_code')} "
+                f"errors={payload.get('error_count',0)} "
+                f"duration={payload.get('duration_sec',0)}s "
+                f"tokens={payload.get('tokens_sent',0)}+{payload.get('tokens_received',0)}")
+    return str(payload)[:200]
diff --git a/apps/api/tests/test_aider_event_service.py b/apps/api/tests/test_aider_event_service.py
new file mode 100644
index 00000000..403038cb
--- /dev/null
+++ b/apps/api/tests/test_aider_event_service.py
@@ -0,0 +1,93 @@
+# Test aider_event_service | 2026-04-20 @ Asia/Taipei
+import pytest
+from datetime import datetime, timezone, timedelta
+from src.services.aider_event_service import (
+    classify_severity, should_create_incident, build_signal_data,
+)
+from src.models.aider import AiderEventIn
+
+TAIPEI = timezone(timedelta(hours=8))
+
+
+def _ev(t, p=None, sid="s1"):
+    return AiderEventIn(
+        ts=datetime.now(TAIPEI), session_id=sid,
+        host="ogt-mac", type=t, payload=p or {},
+    )
+
+
+def test_classify_error_is_warning():
+    # aider "error" event → signal severity "warning" → Severity.P2
+    assert classify_severity(_ev("error")) == "warning"
+
+
+def test_classify_silent_timeout_is_info():
+    # silent_timeout → "info" → P3
+    assert classify_severity(_ev("silent_timeout")) == "info"
+
+
+def test_classify_session_end_nonzero_exit_is_warning():
+    assert classify_severity(_ev("session_end", {"exit_code": 1})) == "warning"
+
+
+def test_classify_session_end_multi_error_is_high():
+    # 3+ errors + nonzero exit → "high" → P1
+    assert classify_severity(_ev("session_end", {"exit_code": 1, "error_count": 5})) == "high"
+
+
+def test_classify_session_end_clean_is_none():
+    ev = _ev("session_end", {"exit_code": 0, "error_count": 0})
+    assert classify_severity(ev) is None
+    assert should_create_incident(ev) is False
+
+
+def test_classify_session_start_is_none():
+    assert should_create_incident(_ev("session_start")) is False
+
+
+def test_classify_error_triggers_incident():
+    assert should_create_incident(_ev("error")) is True
+
+
+def test_build_signal_data_fingerprint_per_session_type():
+    # 同 session + 同 type → 同 fingerprint（讓既有 3min debounce 生效）
+    sd1 = build_signal_data(_ev("error", {"cwd": "/a", "model": "m"}, sid="sx"))
+    sd2 = build_signal_data(_ev("error", {"cwd": "/a", "model": "m"}, sid="sx"))
+    assert sd1["fingerprint"] == sd2["fingerprint"]
+    assert sd1["fingerprint"].startswith("aider:sx:error")
+
+
+def test_build_signal_data_different_sessions_different_fp():
+    sd_a = build_signal_data(_ev("error", sid="sA"))
+    sd_b = build_signal_data(_ev("error", sid="sB"))
+    assert sd_a["fingerprint"] != sd_b["fingerprint"]
+
+
+def test_build_signal_data_shape():
+    ev = _ev("error", {"cwd": "/Users/ogt/awoooi", "model": "elephant-alpha",
+                       "message": "api timeout", "kind": "api_rate_limit"})
+    sd = build_signal_data(ev)
+    # 必要 keys
+    for k in ("alert_name", "severity", "source", "fingerprint", "target",
+              "labels", "annotations"):
+        assert k in sd, f"missing {k}"
+    assert sd["source"] == "manual"
+    assert sd["target"] == "awoooi"  # 從 cwd basename
+    assert sd["labels"]["session_id"] == "s1"
+    assert sd["labels"]["model"] == "elephant-alpha"
+
+
+def test_build_signal_data_redacts_secrets_in_annotations():
+    """secret 不可進 annotations/labels"""
+    ev = _ev("error", {"cwd": "/r", "model": "m",
+                        "message": "key sk-or-v1-abcdef0123456789ABCDEFghijklmnopqrstuv fail"})
+    sd = build_signal_data(ev)
+    # annotations 可能含 message — 需已遮罩
+    annot_str = str(sd["annotations"])
+    assert "sk-or-v1-abcdef" not in annot_str
+    assert "<redacted:" in annot_str
+
+
+def test_build_signal_data_returns_none_for_non_incident_types():
+    # session_start 不該建 signal
+    assert build_signal_data(_ev("session_start")) is None