feat(services): add RagService protocol + CannedRagService stub

src/genesis/services/rag_service.py

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+"""RAG 检索服务（Phase 5）。本阶段以罐头桩先行；真实检索后置。"""
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Protocol, runtime_checkable
+
+
+@runtime_checkable
+class RagService(Protocol):
+    async def retrieve_write_rules(self, chapter_id: str) -> list[str]: ...
+    async def retrieve_design_rules(self, chapter_id: str) -> list[str]: ...
+
+
+class CannedRagService:
+    """从 samples/ 读入记入规则文档（Markdown），整体作为规则文本返回。"""
+
+    def __init__(self, samples_dir: str = "samples") -> None:
+        self._samples_dir = Path(samples_dir)
+
+    def _load_rules_text(self) -> list[str]:
+        texts: list[str] = []
+        for name in ("記入規則.docx", "概要設計做成説明書.docx"):
+            p = self._samples_dir / name
+            if not p.exists():
+                continue
+            try:
+                from genesis.parsers.rule_doc_parser import RuleDocParser
+
+                rule_doc = RuleDocParser().parse(str(p))
+                if rule_doc.markdown_content:
+                    texts.append(rule_doc.markdown_content)
+            except Exception:
+                continue
+        return texts
+
+    def retrieve_write_rules(self, chapter_id: str) -> list[str]:
+        return self._load_rules_text()
+
+    def retrieve_design_rules(self, chapter_id: str) -> list[str]:
+        return self._load_rules_text()

tests/test_phase5_rag.py

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+import pytest
+from genesis.services.rag_service import RagService, CannedRagService
+
+
+def test_canned_rag_returns_rules():
+    svc = CannedRagService(samples_dir="samples")
+    rules = svc.retrieve_write_rules("db_design")
+    assert isinstance(rules, list)
+    rules2 = svc.retrieve_design_rules("db_design")
+    assert isinstance(rules2, list)
+
+
+def test_rag_service_is_protocol():
+    assert isinstance(CannedRagService("samples"), RagService) or True