refactor(flywheel): 首席架構師審查修正 C1/C2/I1/I2/I3/I4/M1

C1 — Repository 層修正 (積木化鐵律):
  新增 PlaybookEmbeddingRepository (pgvector UPSERT)
  playbook_embedding_service 改透過 Repository 存取 DB，不再直接 db.execute(text(...))

C2 — Router 層業務邏輯移入 Service 層:
  create_incident_for_approval + extract_affected_services (去掉底線前綴) 移入 incident_service.py
  webhooks.py 改從 incident_service import，自身不再含業務邏輯

I1 — _infra_jobs 提升為 module-level frozenset (_INFRA_JOB_NAMES)，避免每次呼叫重建

I2 — _persist_embeddings_to_db 補齊 PlaybookRAGService / list[Playbook] 型別標注

I3 — embedding 格式顯式化: "[" + ",".join(str(float(x)) for x in embedding) + "]"
  防止 pgvector 因格式差異靜默解析失敗

I4 — import asyncio 移至 main.py 頂層，移除 try 區塊內重複 import

M1 — similarity.py: 移除死代碼 `if union > 0 else 0.0`
  union 在兩個集合都非空時不可能為 0

2026-04-10 Asia/Taipei — Claude Sonnet 4.6
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/src/repositories/playbook_embedding_repository.py

@@ -0,0 +1,104 @@
+"""
+Playbook Embedding Repository — pgvector 持久化層
+=================================================
+C1 修正 (首席架構師審查 2026-04-10 Claude Sonnet 4.6 Asia/Taipei):
+  違規修復: playbook_embedding_service.py 直接 db.execute(text(...)) 繞過 Repository 層
+  解法: 移至此 Repository，Service 層透過此介面存取
+
+職責: playbook_embeddings 表的 CRUD (pgvector)
+對應遷移: migrations/flywheel_playbook_embeddings.sql
+"""
+
+from __future__ import annotations
+
+import structlog
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import AsyncSession
+
+logger = structlog.get_logger(__name__)
+
+
+class PlaybookEmbeddingRepository:
+    """
+    Playbook Embedding Repository
+
+    職責: playbook_embeddings 表 CRUD
+    使用 pgvector 儲存 nomic-embed-text 768 維向量
+
+    Args:
+        db: SQLAlchemy AsyncSession (DI 注入)
+    """
+
+    def __init__(self, db: AsyncSession) -> None:
+        self._db = db
+
+    async def upsert(
+        self,
+        playbook_id: str,
+        embedding: list[float],
+        alert_names: list[str],
+        keywords: list[str],
+    ) -> bool:
+        """
+        新增或更新 Playbook 向量 (UPSERT)。
+
+        pgvector 格式: '[x,y,z,...]' 字串
+        ON CONFLICT (playbook_id) → 更新向量快照與 updated_at
+
+        Args:
+            playbook_id: Playbook ID
+            embedding: 768 維浮點向量 (list[float])
+            alert_names: 索引時的 alert_names 快照
+            keywords: 索引時的 keywords 快照
+
+        Returns:
+            True 表示成功
+        """
+        try:
+            # 顯式格式化保證 pgvector 可解析，避免 str(list) 空格差異
+            vec_str = "[" + ",".join(str(float(x)) for x in embedding) + "]"
+
+            await self._db.execute(
+                text("""
+                    INSERT INTO playbook_embeddings
+                        (playbook_id, embedding, alert_names, keywords, indexed_at, updated_at)
+                    VALUES
+                        (:playbook_id, :embedding, :alert_names, :keywords, NOW(), NOW())
+                    ON CONFLICT (playbook_id) DO UPDATE SET
+                        embedding   = EXCLUDED.embedding,
+                        alert_names = EXCLUDED.alert_names,
+                        keywords    = EXCLUDED.keywords,
+                        updated_at  = NOW()
+                """),
+                {
+                    "playbook_id": playbook_id,
+                    "embedding": vec_str,
+                    "alert_names": alert_names,
+                    "keywords": keywords,
+                },
+            )
+            return True
+
+        except Exception as e:
+            logger.warning(
+                "playbook_embedding_upsert_failed",
+                playbook_id=playbook_id,
+                error=str(e),
+            )
+            return False
+
+    async def delete(self, playbook_id: str) -> bool:
+        """刪除 Playbook 向量記錄。"""
+        try:
+            await self._db.execute(
+                text("DELETE FROM playbook_embeddings WHERE playbook_id = :pid"),
+                {"pid": playbook_id},
+            )
+            return True
+        except Exception as e:
+            logger.warning(
+                "playbook_embedding_delete_failed",
+                playbook_id=playbook_id,
+                error=str(e),
+            )
+            return False