feat(flywheel): few-shot 在线检索注入打通风险规则编译链路

- 新增 FewShotStore：独立 Qdrant collection few_shot_samples，向量 upsert/search/delete，
  全程失败降级不阻塞主链路
- 新增 FewShotIngestionService：RiskObservation confirmed/false_positive → FewShotSample +
  向量，带 sample_key 幂等去重
- 新增 FewShotRetriever：按 case 特征检索相似历史样本，去重 + token 预算 + 单条字符上限裁剪
- risk_observations.create_feedback commit 后挂 hook 自动入库，带 feature flag 和 try/except 兜底
- risk_rule_generation_prompt 新增 few_shot_samples 可选参数，合并进 examples 并标
  source=historical_confirmed；risk_rule_generation 构造 prompt 前调 retriever，失败降级为空

server/src/app/services/few_shot_retrieval.py

@@ -0,0 +1,122 @@
+"""Few-shot 检索器：按当前 case 特征检索相似历史样本，拼成注入块。
+
+从 :class:`FewShotStore` 取相似样本，转成可供 prompt 构造函数直接使用的结构。
+带 token 预算裁剪和去重，确保不撑爆 prompt。
+
+典型用法（在构造 prompt 之前调用）::
+
+    retriever = FewShotRetriever.from_session(session)
+    samples = retriever.retrieve_for_risk_rule_generation(
+        domain="travel", natural_language="票据城市与申报地不一致"
+    )
+    messages = build_risk_rule_compiler_messages(
+        ...,
+        few_shot_samples=samples,
+    )
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from sqlalchemy.orm import Session
+
+from app.core.logging import get_logger
+from app.services.embedding_provider import EmbeddingProvider
+from app.services.few_shot_store import FewShotStore
+
+logger = get_logger("app.services.few_shot_retrieval")
+
+# 单条 few-shot 样本估算 token 数（用于预算裁剪）
+SAMPLE_TOKEN_BUDGET = 1200
+# 单条样本最大字符数，超长直接截断结论，避免撑爆 prompt
+SINGLE_SAMPLE_MAX_CHARS = 400
+# 历史样本最多注入条数（与原内置 examples 合并后总量受限）
+MAX_HISTORICAL_SAMPLES = 3
+
+
+class FewShotRetriever:
+    """按 case 特征检索已确认样本，返回 prompt 可直接消费的结构。"""
+
+    def __init__(self, store: FewShotStore) -> None:
+        self._store = store
+
+    @classmethod
+    def from_session(cls, session: Session) -> "FewShotRetriever":
+        provider = EmbeddingProvider.from_settings(session)
+        return cls(FewShotStore(provider))
+
+    def retrieve_for_risk_rule_generation(
+        self,
+        *,
+        domain: str = "",
+        risk_type: str = "",
+        natural_language: str,
+        top_k: int = MAX_HISTORICAL_SAMPLES,
+    ) -> list[dict[str, Any]]:
+        """检索与当前规则需求相似的历史样本，返回注入块列表。"""
+
+        case_text = self._build_case_text(
+            natural_language=natural_language,
+            domain=domain,
+            risk_type=risk_type,
+        )
+        if not case_text:
+            return []
+        hits = self._store.search(
+            case_text,
+            scene="risk_rule_generation",
+            labels=["confirmed", "false_positive"],
+            top_k=top_k,
+        )
+        return self._hits_to_injection_blocks(hits)
+
+    def _build_case_text(
+        self,
+        *,
+        natural_language: str,
+        domain: str = "",
+        risk_type: str = "",
+    ) -> str:
+        parts = [natural_language, domain, risk_type]
+        return "\n".join(p for p in parts if p).strip()
+
+    def _hits_to_injection_blocks(
+        self,
+        hits: list[dict[str, Any]],
+    ) -> list[dict[str, Any]]:
+        """把检索命中转成 prompt 可消费的块，做去重和预算裁剪。"""
+
+        blocks: list[dict[str, Any]] = []
+        seen_conclusions: set[str] = set()
+        budget = SAMPLE_TOKEN_BUDGET
+        for hit in hits:
+            conclusion = (hit.get("conclusion_text") or "").strip()
+            if not conclusion or conclusion in seen_conclusions:
+                continue
+            # 超长结论截断到上限，避免单条样本占用过多预算
+            if len(conclusion) > SINGLE_SAMPLE_MAX_CHARS:
+                conclusion = conclusion[:SINGLE_SAMPLE_MAX_CHARS]
+            payload = hit.get("payload_json") or {}
+            block = {
+                "source": "historical_confirmed",
+                "label": hit.get("label"),
+                "domain": hit.get("domain") or "",
+                "risk_type": hit.get("risk_type") or "",
+                "score": round(float(hit.get("score") or 0.0), 4),
+                "conclusion": conclusion,
+                "context": {
+                    "risk_signal": payload.get("risk_signal") or "",
+                    "risk_level": payload.get("risk_level") or "",
+                    "ontology": payload.get("ontology") or {},
+                    "feedback_comment": payload.get("feedback_comment") or "",
+                },
+            }
+            # 粗略 token 估算（按字符数 / 1.6 近似中文 token 比）
+            estimated_tokens = int(len(conclusion) / 1.6) + 40
+            if estimated_tokens > budget:
+                break
+            budget -= estimated_tokens
+            blocks.append(block)
+            seen_conclusions.add(conclusion)
+        return blocks