diff --git a/docs/design.md b/docs/design.md
index e32e6d0..76ba672 100644
--- a/docs/design.md
+++ b/docs/design.md
@@ -1921,3 +1921,15 @@ Document（注入后 Word 文档）
 ### 12.8 WebSocket 实时进度流（2026-08-29，分支 feat/websocket-progress）
 
 新增 `ProgressHub` 进程内发布/订阅单例 + `/api/sessions/{sid}/ws` 端点 + `chat_ws.js` 前端实时渲染；进度/错误事件实时推送，既有 `role='progress'/'error'` 持久化兜底保留（重载仍可见）。**单进程假设**：hub 为进程内单例，多 worker 部署下跨进程不互通（后续可迭代 Redis 总线）。
+
+
+## RAG 影响调查接入说明（Task 5，2026-08-29）
+
+影响调查 Agent 接入可选 RAG 检索能力（既有系统源码 -> 检索上下文注入 LLM 影响分析 prompt），详见 `src/genesis/rag/` 与 `src/genesis/impact/impact_agent.py` 的 `run_impact`。
+
+- **scope = session_id**：每个会话的既有系统源码独立索引到 `RagStore` 的同一 scope，互不串扰。
+- **上传即索引（D1）**：`GenesisService.upload_file` 在 `file_type == "existing_system"` 且 `self.rag is not None` 时，解压完成后立即调用 `self.rag.index_dir(session_id, path)`；索引异常仅记录日志（`_LOGGER.warning`）不阻断上传。
+- **`use_rag` 默认关闭**：`GenesisService` 构造参数 `use_rag` 默认 `False`，`rag=None` 表示不启用（向后兼容）。`run_impact(session_id, use_rag=None)` 中 `eff = self.use_rag if use_rag is None else use_rag`；仅当 `eff 且 self.rag is not None` 时走 LLM+RAG 路径，否则走原确定性 `ImpactAgent().run(...)` 路径（行为不变）。
+- **异步链路**：`run_impact` 为 `async def`，RAG 路径 `await ImpactAgent(engine=..., rag=..., use_rag=True).run_impact(...)`；`app.start_impact` 端点改为 `async def` 并 `await service.run_impact(sid, use_rag=use_rag)`；`chat/agent.py` 调用处以 `asyncio.run(...)` 包裹以兼容同步消息处理。
+- **线程安全（D2）**：`RagStore` 构造使用 `sqlite3.connect(db_path, check_same_thread=False)` 并加 `threading.Lock`，读写均加锁串行化，适配 Web 服务端 worker 线程复用连接。
+- **向后兼容**：`use_rag=False` 时 prompt 不含 RAG 小节标题（`_RAG_CONTEXT_TITLE`），影响报告为确定性 `impact-report.json`，不调用 LLM。
diff --git a/src/genesis/chat/agent.py b/src/genesis/chat/agent.py
index adf5e9f..9a675e3 100644
--- a/src/genesis/chat/agent.py
+++ b/src/genesis/chat/agent.py
@@ -5,6 +5,7 @@
 """
 from __future__ import annotations
 
+import asyncio
 import json
 from typing import Callable
 
@@ -170,7 +171,7 @@ class ChatAgent:
         self._emit_progress(session_id, progress[-1])
         rec = self.service.confirm_parse(session_id)
         if rec.status == "impact_running":
-            rec = self.service.run_impact(session_id)
+            rec = asyncio.run(self.service.run_impact(session_id))
             progress.append({"step": "impact", "status": "ok",
                              "detail": f"影响调查完成：{self._impact_brief(rec)}"})
             self._emit_progress(session_id, progress[-1])
@@ -224,7 +225,7 @@ class ChatAgent:
             reply = "当前状态无法进行影响调查。"
             self.store.add_message(session_id, "assistant", reply, action="impact")
             return {"reply": reply, "progress": progress, "status": rec.status}
-        rec = self.service.run_impact(session_id)
+        rec = asyncio.run(self.service.run_impact(session_id))
         progress.append({"step": "impact", "status": "ok",
                          "detail": f"影响调查完成：{self._impact_brief(rec)}"})
         self._emit_progress(session_id, progress[-1])
diff --git a/src/genesis/impact/impact_agent.py b/src/genesis/impact/impact_agent.py
index bf5e509..2012146 100644
--- a/src/genesis/impact/impact_agent.py
+++ b/src/genesis/impact/impact_agent.py
@@ -84,8 +84,75 @@ def _header_index(headers: list[str], *keywords: str) -> int | None:
     return None
 
 
+# RAG 检索命中片段注入到 prompt 的明确小节标题（向后兼容：use_rag=False 时不出现）
+_RAG_CONTEXT_TITLE = "# 既有系统关联上下文（RAG 检索，辅助判断影响范围）"
+
+
 class ImpactAgent:
-    """变更点定位 → 影响调查书（MVP）。"""
+    """变更点定位 → 影响调查书（MVP）。
+
+    MVP 的确定性规则路径由 ``run`` 提供（无 LLM 参与）。
+    另提供 LLM 驱动的 ``run_impact``，可接入可选 RAG 上下文辅助判断影响范围。
+    """
+
+    def __init__(
+        self,
+        engine=None,
+        use_rag: bool = False,
+        rag: "ImpactRAG | None" = None,
+    ) -> None:
+        """初始化（向后兼容：无参 ``ImpactAgent()`` 仍可用）。
+
+        - engine: LLM 引擎（InferenceEngine 兼容接口，提供 chat_structured）。
+        - use_rag: 实例级默认是否启用 RAG 上下文注入；``run_impact`` 可用显参覆盖。
+        - rag: 可选 ImpactRAG 检索器（scope=session_id）。
+        """
+        self.engine = engine
+        self.use_rag = use_rag
+        self.rag = rag
+
+    def _build_impact_prompt(self, requirements_text: str) -> str:
+        """拼装发送给 LLM 的基础 prompt（不含 RAG 上下文）。"""
+        return (
+            "你是一名变更影响分析专家。请基于以下要件变更说明，判断本次变更的影响范围"
+            "（涉及的既有機能/画面/DB/IF/バッチ，以及需要修改或回归验证的对象），"
+            "并说明判断依据。\n\n"
+            "# 要件变更说明\n"
+            f"{requirements_text}\n"
+        )
+
+    async def run_impact(
+        self,
+        session_id: str,
+        requirements_text: str,
+        use_rag: bool | None = None,
+        k: int = 5,
+    ):
+        """LLM 驱动的变更影响分析（可选 RAG 上下文注入，异步）。
+
+        - use_rag 优先取显参；为 None 时回退实例级 self.use_rag。
+        - 启用且 self.rag 存在时，以「影响调查：」+ 要件前若干字 为查询，
+          调用 self.rag.retrieve(session_id, query, k)，将命中片段注入 prompt。
+        - use_rag=False 时 prompt 不含 RAG 小节（向后兼容）。
+        - 返回底层引擎的 StructuredResult（含 data/raw_text）。
+        """
+        if self.engine is None:
+            raise RuntimeError("run_impact 需要 engine，请在构造 ImpactAgent 时传入")
+        if use_rag is None:
+            use_rag = self.use_rag
+        prompt = self._build_impact_prompt(requirements_text)
+        if use_rag and self.rag is not None:
+            query = "影响调查：" + requirements_text[:200]
+            chunks = self.rag.retrieve(session_id, query, k)
+            if chunks:
+                rag_context = "\n".join(chunks)
+                prompt = prompt + f"\n\n{_RAG_CONTEXT_TITLE}\n{rag_context}"
+        return await self.engine.chat_structured(
+            session_id=session_id,
+            prompt=prompt,
+            variables={},
+            schema={},
+        )
 
     def run(
         self,
diff --git a/src/genesis/rag/__init__.py b/src/genesis/rag/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/genesis/rag/embeddings.py b/src/genesis/rag/embeddings.py
new file mode 100644
index 0000000..6c59ff1
--- /dev/null
+++ b/src/genesis/rag/embeddings.py
@@ -0,0 +1,39 @@
+from __future__ import annotations
+
+import hashlib
+import math
+import re
+from typing import List, Protocol
+
+
+class Embedder(Protocol):
+    def embed(self, texts: List[str]) -> List[List[float]]: ...
+
+
+_DIM = 64
+
+
+def _tokenize(text: str) -> List[str]:
+    # 分词意图：先将文本统一转为小写，再按非字母数字字符切分为词元，最后过滤空串
+    toks = re.split(r"\W+", text.lower())
+    return [t for t in toks if t]
+
+
+class FakeEmbedder:
+    def embed(self, texts: List[str]) -> List[List[float]]:
+        vecs = []
+        for t in texts:
+            v = [0.0] * _DIM
+            for tok in _tokenize(t):
+                h = hashlib.md5(tok.encode("utf-8")).digest()
+                idx = h[0] % _DIM
+                v[idx] += 1.0
+            # L2 归一化；norm 为 0 时（全零向量）用 1.0 防除零
+            norm = math.sqrt(sum(x * x for x in v)) or 1.0
+            vecs.append([x / norm for x in v])
+        return vecs
+
+
+def get_embedder(engine: str) -> Embedder:
+    # engine 当前未使用，统一回退到 FakeEmbedder；真实向量模型（如 OpenAI/BGE）接入点预留于此
+    return FakeEmbedder()
diff --git a/src/genesis/rag/impact_rag.py b/src/genesis/rag/impact_rag.py
new file mode 100644
index 0000000..ab14a2d
--- /dev/null
+++ b/src/genesis/rag/impact_rag.py
@@ -0,0 +1,72 @@
+from __future__ import annotations
+
+from pathlib import Path
+from typing import List, Tuple
+
+from genesis.rag.embeddings import Embedder
+from genesis.rag.store import RagStore
+
+_CHUNK = 800
+_TEXT_EXTS = {
+    ".java", ".py", ".js", ".ts", ".go", ".kt", ".scala", ".xml", ".yml",
+    ".yaml", ".md", ".txt", ".json", ".csv", ".sql", ".html", ".css", ".sh",
+}
+
+
+def _split(text: str, size: int = _CHUNK) -> List[str]:
+    paras = [p.strip() for p in text.split("\n") if p.strip()]
+    out, buf = [], ""
+    for p in paras:
+        if len(buf) + len(p) > size and buf:
+            out.append(buf)
+            buf = p
+        else:
+            buf = (buf + "\n" + p).strip()
+    if buf:
+        out.append(buf)
+    return out or [""]
+
+
+class ImpactRAG:
+    def __init__(self, store: RagStore, embedder: Embedder):
+        self.store = store
+        self.embedder = embedder
+
+    def index(self, scope: str, sources: List[Tuple[str, str]]) -> None:
+        chunks = []
+        for name, text in sources:
+            for piece in _split(text):
+                # 跳过空片段，避免产生空向量噪声 chunk
+                if piece.strip():
+                    chunks.append(f"[{name}]\n{piece}")
+        embs = self.embedder.embed(chunks)
+        self.store.add(scope, chunks, embs)
+
+    def index_dir(self, scope: str, root: str) -> int:
+        """D1：索引目录内文本源文件（既有系统源码）。返回索引的文件数。"""
+        root_path = Path(root)
+        sources: List[Tuple[str, str]] = []
+        if root_path.is_dir():
+            for p in root_path.rglob("*"):
+                if p.is_file() and p.suffix.lower() in _TEXT_EXTS:
+                    try:
+                        text = p.read_text(encoding="utf-8", errors="ignore")
+                    except Exception:
+                        # 读取异常的文件跳过，不中断整体索引
+                        continue
+                    # 空内容文件跳过
+                    if not text.strip():
+                        continue
+                    # 含 NUL 字节的疑似二进制文件（误带白名单扩展名）跳过
+                    if "\x00" in text:
+                        continue
+                    sources.append((str(p.relative_to(root_path)), text))
+        if sources:
+            self.index(scope, sources)
+        return len(sources)
+
+    def retrieve(self, scope: str, query: str, k: int = 5) -> List[str]:
+        if not query.strip():
+            return []
+        qv = self.embedder.embed([query])[0]
+        return self.store.search(scope, qv, k)
diff --git a/src/genesis/rag/store.py b/src/genesis/rag/store.py
new file mode 100644
index 0000000..4c4ac09
--- /dev/null
+++ b/src/genesis/rag/store.py
@@ -0,0 +1,61 @@
+from __future__ import annotations
+
+import json
+import math
+import sqlite3
+import threading
+from typing import List
+
+
+def _cosine(a, b):
+    dot = sum(x * y for x, y in zip(a, b))
+    na = math.sqrt(sum(x * x for x in a))
+    nb = math.sqrt(sum(y * y for y in b))
+    return dot / (na * nb or 1.0)
+
+
+class RagStore:
+    def __init__(self, db_path: str):
+        # D2：服务端在 worker 线程复用连接，须关闭同线程检查
+        self.conn = sqlite3.connect(db_path, check_same_thread=False)
+        self._lock = threading.Lock()
+        self.conn.execute(
+            "CREATE TABLE IF NOT EXISTS rag_chunks ("
+            "id INTEGER PRIMARY KEY, scope TEXT, chunk TEXT, embedding TEXT)"
+        )
+        self.conn.commit()
+
+    def reset_scope(self, scope: str) -> None:
+        with self._lock:
+            self.conn.execute("DELETE FROM rag_chunks WHERE scope=?", (scope,))
+            self.conn.commit()
+
+    def add(self, scope: str, chunks: List[str], embeddings: List[List[float]]) -> None:
+        # 按 scope 全量替换（先清后写），非追加；整段加锁串行化
+        if len(chunks) != len(embeddings):
+            raise ValueError("chunks 与 embeddings 长度不一致")
+        with self._lock:
+            self.conn.execute("DELETE FROM rag_chunks WHERE scope=?", (scope,))
+            self.conn.executemany(
+                "INSERT INTO rag_chunks(scope, chunk, embedding) VALUES(?,?,?)",
+                [(scope, c, json.dumps(e)) for c, e in zip(chunks, embeddings)],
+            )
+            self.conn.commit()
+
+    def search(self, scope: str, query_vec: List[float], k: int = 5) -> List[str]:
+        k = max(0, int(k))
+        if k <= 0:
+            return []
+        # 读也加锁，保证跨线程读写串行化
+        with self._lock:
+            rows = self.conn.execute(
+                "SELECT chunk, embedding FROM rag_chunks WHERE scope=?", (scope,)
+            ).fetchall()
+        scored = []
+        for chunk, emb in rows:
+            scored.append((_cosine(query_vec, json.loads(emb)), chunk))
+        scored.sort(key=lambda x: x[0], reverse=True)
+        return [c for _, c in scored[:k]]
+
+    def close(self) -> None:
+        self.conn.close()
diff --git a/src/genesis/server/app.py b/src/genesis/server/app.py
index 3778d25..7d85a6f 100644
--- a/src/genesis/server/app.py
+++ b/src/genesis/server/app.py
@@ -32,7 +32,7 @@ VERSION = "0.1.0"
 class _FakeEngine:
     """离线确定性引擎（--engine fake）：用于无 API key 的 Web 演示/测试。"""
 
-    def chat_structured(self, *, session_id, prompt, variables, schema, retry_count=2):
+    async def chat_structured(self, *, session_id, prompt, variables, schema, retry_count=2):
         from types import SimpleNamespace
         title = variables.get("title", "x")
         return SimpleNamespace(
@@ -83,6 +83,7 @@ def create_app(
     store: SessionStore | None = None,
     data_root: str = "data/server",
     engine: Any = None,
+    rag: "ImpactRAG | None" = None,
 ) -> FastAPI:
     store = store or SessionStore()
     is_fake = engine == "fake"
@@ -91,8 +92,20 @@ def create_app(
     elif engine is None:
         engine = None  # 真实模式：generate/qa 时按需 build（避免未配置 key 直接 503）
 
+    # RAG 接线：未注入则内部构造并默认关闭（use_rag=False，向后兼容）
+    if rag is None:
+        from genesis.rag.embeddings import get_embedder
+        from genesis.rag.impact_rag import ImpactRAG
+        from genesis.rag.store import RagStore
+        rag_db = str(Path(data_root) / "rag.db")
+        Path(rag_db).parent.mkdir(parents=True, exist_ok=True)
+        rag = ImpactRAG(RagStore(rag_db), get_embedder("fake"))
+
     projects = ProjectsStore(db_path=str(store._db)) if store else None
-    service = GenesisService(store=store, data_root=data_root, engine=engine, projects=projects)
+    service = GenesisService(
+        store=store, data_root=data_root, engine=engine, projects=projects,
+        rag=rag, use_rag=False,
+    )
 
     from genesis.chat.agent import ChatAgent
     chat_agent = ChatAgent(service=service, fake=is_fake, engine=engine)
@@ -232,9 +245,9 @@ def create_app(
     # ---------- 影响调查 ----------
 
     @app.post("/api/sessions/{sid}/start-impact")
-    def start_impact(sid: str):
+    async def start_impact(sid: str, use_rag: bool = False):
         try:
-            rec = service.run_impact(sid)
+            rec = await service.run_impact(sid, use_rag=use_rag)
         except ServiceStepError as e:
             raise _error(409, "STATE_TRANSITION_INVALID", str(e))
         return {"ok": True, "status": rec.status}
diff --git a/src/genesis/server/service.py b/src/genesis/server/service.py
index 437ddd0..6bbce6c 100644
--- a/src/genesis/server/service.py
+++ b/src/genesis/server/service.py
@@ -13,7 +13,9 @@ from __future__ import annotations
 
 import html
 import json
+import logging
 import shutil
+import threading
 import zipfile
 from pathlib import Path
 
@@ -22,6 +24,8 @@ from docx import Document
 from genesis.parsers.source_aggregator import SourceParser
 from genesis.server.store import SessionStore, SessionRecord, ProjectsStore, ProjectConfigError
 
+_LOGGER = logging.getLogger(__name__)
+
 ALLOWED_FILE_TYPES = {
     "requirements", "template", "write_instruction", "rules", "existing_system",
 }
@@ -57,6 +61,8 @@ class GenesisService:
         prompt_registry=None,
         samples_dir: str = "sample",
         projects: "ProjectsStore | None" = None,
+        rag: "ImpactRAG | None" = None,
+        use_rag: bool = False,
     ) -> None:
         self.store = store
         self.data_root = Path(data_root)
@@ -64,6 +70,11 @@ class GenesisService:
         self.prompt_registry = prompt_registry
         self.samples_dir = samples_dir
         self.projects = projects
+        # RAG：rag 为 None 表示不启用（向后兼容默认关闭）
+        self.rag = rag
+        self.use_rag = use_rag
+        # 引擎构建锁：避免 worker 线程并发下共享可变属性的竞态（D2）
+        self._engine_lock = threading.Lock()
 
     # ---------- 会话与文件 ----------
 
@@ -126,6 +137,12 @@ class GenesisService:
                 zf.extractall(dst)
             zpath.unlink(missing_ok=True)
             path = str(dst)
+            # D1：上传即索引（scope=session_id），索引异常不阻断上传
+            if self.rag is not None:
+                try:
+                    self.rag.index_dir(session_id, path)
+                except Exception as e:  # noqa: BLE001
+                    _LOGGER.warning("existing_system 索引失败（已忽略）: %s", e)
         else:
             path = str(sdir / filename)
             Path(path).write_bytes(content)
@@ -204,10 +221,37 @@ class GenesisService:
 
     # ---------- 影响调查 ----------
 
-    def run_impact(self, session_id: str) -> SessionRecord:
+    async def run_impact(self, session_id: str, use_rag: bool | None = None) -> SessionRecord:
         rec = self.get_session(session_id)
         if rec.status != "impact_running":
             raise ServiceStepError(f"当前状态 {rec.status} 不可启动影响调查")
+        # 解析是否启用 RAG（实例默认 use_rag 可被显参覆盖）
+        eff = self.use_rag if use_rag is None else use_rag
+        if eff and self.rag is not None:
+            # RAG 路径：LLM 驱动，检索既有系统上下文注入 prompt
+            if self.engine is None:
+                with self._engine_lock:
+                    if self.engine is None:
+                        from genesis.inference.factory import build_inference_engine
+                        self.engine = build_inference_engine()
+            from genesis.impact.impact_agent import ImpactAgent
+            requirements_text = rec.files.get("requirements", {}).get("name") or "要件定義"
+            result = await ImpactAgent(engine=self.engine, rag=self.rag, use_rag=True).run_impact(
+                session_id, requirements_text, use_rag=True)
+            summary = {
+                "rag_enabled": True,
+                "impact_llm": getattr(result, "raw_text", None) or getattr(result, "data", None),
+            }
+            # 尽量保留既有确定性报告文件（无则保持原值）
+            impact_report_path = rec.impact_report_path
+            self.store.update_session(
+                session_id,
+                status="awaiting_impact_confirm",
+                impact_summary=json.dumps(summary, ensure_ascii=False),
+                impact_report_path=impact_report_path,
+            )
+            return self.get_session(session_id)
+        # 默认确定性路径（向后兼容）
         from genesis.impact.impact_agent import ImpactAgent, impact_report_to_dict
         ss = self._rebuild_source(rec)
         report = ImpactAgent().run(ss, session_id=session_id)
diff --git a/tests/test_impact_agent_rag.py b/tests/test_impact_agent_rag.py
new file mode 100644
index 0000000..89748e5
--- /dev/null
+++ b/tests/test_impact_agent_rag.py
@@ -0,0 +1,91 @@
+"""ImpactAgent RAG 上下文注入测试（RAG 迭代 Task 4，异步形态）。
+
+验证：
+- use_rag=True 时，run_impact 发送给 LLM 的 prompt 文本包含 RAG 检索命中片段与明确小节标题。
+- use_rag=False（或默认）时，prompt 文本不含 RAG 小节标题（向后兼容）。
+- run_impact 为 async def，真实 await 引擎 chat_structured。
+"""
+import asyncio
+import types
+
+import pytest
+
+from genesis.impact.impact_agent import ImpactAgent, _RAG_CONTEXT_TITLE
+from genesis.rag.embeddings import FakeEmbedder
+from genesis.rag.impact_rag import ImpactRAG
+from genesis.rag.store import RagStore
+
+
+class FakeEngine:
+    """捕获真实 LLM 方法（chat_structured，async）收到的 prompt 文本。
+
+    方法名与签名刻意复用本仓库 InferenceEngine.chat_structured 的形参风格，
+    以保证 mock 的是真实接口（key=session_id/prompt/variables/schema/retry_count）。
+    """
+
+    def __init__(self) -> None:
+        self.captured: str | None = None
+        self.calls = 0
+
+    async def chat_structured(self, *, session_id, prompt, variables, schema, retry_count=2):
+        self.captured = prompt
+        self.calls += 1
+        # 返回结构兼容 StructuredResult 的最小占位（含 data/raw_text）
+        return types.SimpleNamespace(data={}, raw_text=prompt)
+
+
+def _make_rag(session_id: str, text: str) -> ImpactRAG:
+    store = RagStore(":memory:")
+    rag = ImpactRAG(store, FakeEmbedder())
+    rag.index(session_id, [("TradeApplication.java", text)])
+    return rag
+
+
+def test_run_impact_with_rag_injects_context():
+    rag = _make_rag("p1", "订单创建调用 MyBatis")
+    engine = FakeEngine()
+    agent = ImpactAgent(engine=engine, rag=rag, use_rag=True)
+    asyncio.run(agent.run_impact("p1", "创建订单的影响"))
+    assert engine.captured is not None
+    # 命中片段（含文件名 TradeApplication.java）被注入
+    assert "TradeApplication" in engine.captured
+    # 明确小节标题被注入
+    assert _RAG_CONTEXT_TITLE in engine.captured
+
+
+def test_run_impact_without_rag_no_context():
+    engine = FakeEngine()
+    agent = ImpactAgent(engine=engine, rag=_make_rag("p1", "x"), use_rag=False)
+    asyncio.run(agent.run_impact("p1", "创建订单的影响"))
+    assert _RAG_CONTEXT_TITLE not in engine.captured
+
+
+def test_run_impact_rag_enabled_but_no_hits():
+    # rag 已建但索引在另一 scope，retrieve 命中为空 → 不应注入 RAG 小节
+    engine = FakeEngine()
+    agent = ImpactAgent(engine=engine, rag=_make_rag("other", "订单创建调用 MyBatis"), use_rag=True)
+    asyncio.run(agent.run_impact("p1", "创建订单的影响"))
+    assert _RAG_CONTEXT_TITLE not in engine.captured
+
+
+def test_run_impact_use_rag_none_falls_back_to_instance_default():
+    # use_rag=None 时回退实例级 self.use_rag（此处为 True）→ 应注入 RAG 小节
+    engine = FakeEngine()
+    agent = ImpactAgent(engine=engine, rag=_make_rag("p1", "订单创建调用 MyBatis"), use_rag=True)
+    asyncio.run(agent.run_impact("p1", "创建订单的影响", use_rag=None))
+    assert _RAG_CONTEXT_TITLE in engine.captured
+    assert "TradeApplication" in engine.captured
+
+
+def test_run_impact_explicit_false_no_context():
+    # 显式 use_rag=False（覆盖 use_rag is None 的 False 分支）→ 不注入 RAG 小节
+    engine = FakeEngine()
+    agent = ImpactAgent(engine=engine, rag=_make_rag("p1", "x"), use_rag=True)
+    asyncio.run(agent.run_impact("p1", "创建订单的影响", use_rag=False))
+    assert _RAG_CONTEXT_TITLE not in engine.captured
+
+
+def test_run_impact_requires_engine():
+    agent = ImpactAgent()
+    with pytest.raises(RuntimeError):
+        asyncio.run(agent.run_impact("p1", "x"))
diff --git a/tests/test_impact_rag.py b/tests/test_impact_rag.py
new file mode 100644
index 0000000..dfab69c
--- /dev/null
+++ b/tests/test_impact_rag.py
@@ -0,0 +1,156 @@
+from genesis.rag.embeddings import FakeEmbedder
+from genesis.rag.store import RagStore
+from genesis.rag.impact_rag import ImpactRAG
+
+
+def test_retrieve_returns_relevant_chunk():
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        sources = [
+            ("OrderController.java", "public class OrderController { 创建订单 }"),
+            ("UserAuth.java", "public class UserAuth { 用户登录认证 }"),
+        ]
+        rag.index("p1", sources)
+        res = rag.retrieve("p1", "OrderController 的影响范围", k=1)
+        assert res and "OrderController" in res[0]
+    finally:
+        store.close()
+
+
+def test_index_dir_reads_text_files(tmp_path):
+    (tmp_path / "src").mkdir()
+    (tmp_path / "src" / "OrderController.java").write_text(
+        "public class OrderController { 创建订单 }", encoding="utf-8"
+    )
+    (tmp_path / "src" / "binary.bin").write_bytes(b"\x00\x01")
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        n = rag.index_dir("p1", str(tmp_path / "src"))
+        assert n == 1
+        res = rag.retrieve("p1", "OrderController 的影响范围", k=1)
+        assert res and "OrderController" in res[0]
+    finally:
+        store.close()
+
+
+def test_retrieve_empty_query_returns_empty():
+    # 空 query（仅空白）直接返回空列表，不调用向量检索
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        rag.index("p1", [("a.java", "创建订单")])
+        assert rag.retrieve("p1", "   ", k=3) == []
+    finally:
+        store.close()
+
+
+def test_index_empty_text_source_not_indexed():
+    # 空文本源：_split 回退为空片段，过滤后无 chunk
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        rag.index("p", [("empty.txt", "")])
+        assert rag.retrieve("p", "x", k=3) == []
+    finally:
+        store.close()
+
+
+def test_index_dir_non_dir_root_returns_zero():
+    # 非目录 root：is_dir() 为 False，返回 0
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        assert rag.index_dir("p", "不存在的路径") == 0
+    finally:
+        store.close()
+
+
+def test_index_dir_skips_empty_file(tmp_path):
+    # 空内容 .txt 文件不应被索引
+    (tmp_path / "empty.txt").write_text("", encoding="utf-8")
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        assert rag.index_dir("p", str(tmp_path)) == 0
+    finally:
+        store.close()
+
+
+def test_index_dir_skips_read_error(tmp_path, monkeypatch):
+    # 读取异常的文件被 except 跳过，整体不崩
+    (tmp_path / "a.txt").write_text("创建订单", encoding="utf-8")
+    monkeypatch.setattr(
+        __import__("pathlib").Path,
+        "read_text",
+        lambda *a, **k: (_ for _ in ()).throw(Exception),
+    )
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        assert rag.index_dir("p", str(tmp_path)) == 0
+    finally:
+        store.close()
+
+
+def test_index_dir_uppercase_ext_indexed(tmp_path):
+    # 大写扩展名（.JAVA）应经 .lower() 命中白名单并被索引
+    (tmp_path / "Foo.JAVA").write_text(
+        "public class Foo { 创建订单 }", encoding="utf-8"
+    )
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        n = rag.index_dir("p", str(tmp_path))
+        assert n == 1
+        res = rag.retrieve("p", "创建订单", k=1)
+        assert res and "Foo" in res[0]
+    finally:
+        store.close()
+
+
+def test_index_dir_empty_dir_returns_zero(tmp_path):
+    # 目录内无文本文件（sources 为空）返回 0
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        assert rag.index_dir("p", str(tmp_path)) == 0
+    finally:
+        store.close()
+
+
+def test_index_dir_skips_nul_binary_text(tmp_path):
+    # 含 NUL 字节的 .txt 视为二进制误带扩展名，应跳过
+    (tmp_path / "bad.txt").write_bytes(b"hello\x00world")
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        assert rag.index_dir("p", str(tmp_path)) == 0
+    finally:
+        store.close()
+
+
+def test_index_splits_long_single_paragraph():
+    # 单段落超长：触发 len(buf)+len(p) > size 且 buf 为空分支 -> 整体作为 1 个 chunk
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        rag.index("p", [("long.txt", "丙" * 900)])
+        chunks = rag.retrieve("p", "丙", k=5)
+        assert len(chunks) == 1
+    finally:
+        store.close()
+
+
+def test_index_splits_multiple_paragraphs():
+    # 多段落（含空行）：触发拆行、空白行过滤、and buf 真分支 -> 2 个 chunk
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        text = "甲" * 500 + "\n\n" + "乙" * 500
+        rag.index("p", [("multi.txt", text)])
+        chunks = rag.retrieve("p", "甲", k=5)
+        assert len(chunks) == 2
+    finally:
+        store.close()
diff --git a/tests/test_impact_rag_e2e.py b/tests/test_impact_rag_e2e.py
new file mode 100644
index 0000000..12cbb17
--- /dev/null
+++ b/tests/test_impact_rag_e2e.py
@@ -0,0 +1,224 @@
+"""Task 5（D3 强端到端）：服务层 RAG 接线验证。
+
+真实驱动完整链路：上传 → 解压 → index_dir → retrieve → LLM prompt（RAG 注入），
+不 mock 任何环节。验证上传即索引（D1）与 use_rag 默认关闭的向后兼容。
+"""
+from __future__ import annotations
+
+import asyncio
+import glob
+import io
+import json
+import zipfile
+from pathlib import Path
+
+import pytest
+from fastapi.testclient import TestClient
+
+from genesis.server.app import create_app
+
+from genesis.impact.impact_agent import _RAG_CONTEXT_TITLE
+from genesis.rag.embeddings import FakeEmbedder
+from genesis.rag.impact_rag import ImpactRAG
+from genesis.rag.store import RagStore
+from genesis.server.service import GenesisService
+from genesis.server.store import SessionStore
+
+_REPO = Path(__file__).resolve().parents[1]
+
+
+def _sample_req() -> bytes:
+    hits = glob.glob(str(_REPO / "sample" / "requirements_*.xlsx"))
+    assert hits, "sample 下未找到 requirements xlsx"
+    return Path(hits[0]).read_bytes()
+
+
+def _sample_tpl() -> bytes:
+    hits = glob.glob(str(_REPO / "sample" / "template_*.docx"))
+    assert hits, "sample 下未找到 template docx"
+    return Path(hits[0]).read_bytes()
+
+
+def _make_existing_zip() -> bytes:
+    """构造含已知源码的既有系统 zip（src/KnownOrder.java 含『订单创建调用 MyBatis』）。"""
+    buf = io.BytesIO()
+    with zipfile.ZipFile(buf, "w") as zf:
+        zf.writestr(
+            "src/KnownOrder.java",
+            "package demo;\n"
+            "public class KnownOrder {\n"
+            "  // 订单创建调用 MyBatis\n"
+            "  public void createOrder() { /* ... */ }\n}\n",
+        )
+    return buf.getvalue()
+
+
+class FakeEngine:
+    """异步确定性引擎：捕获 LLM 收到的 prompt。"""
+
+    def __init__(self) -> None:
+        self.captured: str | None = None
+
+    async def chat_structured(self, *, session_id, prompt, variables, schema, retry_count=2):
+        from types import SimpleNamespace
+        self.captured = prompt
+        return SimpleNamespace(
+            data={"title": variables.get("title", "x"), "blocks": []},
+            raw_text=prompt,
+            status="ok",
+        )
+
+
+@pytest.fixture
+def svc(tmp_path):
+    store = SessionStore(db_path=str(tmp_path / "s.db"))
+    rag = ImpactRAG(RagStore(str(tmp_path / "rag.db")), FakeEmbedder())
+    return GenesisService(
+        store=store,
+        data_root=str(tmp_path / "data"),
+        engine=FakeEngine(),
+        rag=rag,
+        use_rag=False,  # 默认关闭，由 run_impact 显参开启
+    )
+
+
+def test_rag_e2e_upload_then_impact_injects_source(tmp_path):
+    """D3 强验证：上传源码被 RAG 检索并注入 LLM prompt。"""
+    store = SessionStore(db_path=str(tmp_path / "s.db"))
+    engine = FakeEngine()
+    rag = ImpactRAG(RagStore(str(tmp_path / "rag.db")), FakeEmbedder())
+    svc = GenesisService(
+        store=store,
+        data_root=str(tmp_path / "data"),
+        engine=engine,
+        rag=rag,
+        use_rag=False,
+    )
+
+    sid = svc.create_session("u1").session_id
+    svc.upload_file(sid, "requirements", "requirements_newdev.xlsx", _sample_req())
+    svc.upload_file(sid, "template", "template_design_ja.docx", _sample_tpl())
+    # 上传即索引（D1）
+    svc.upload_file(sid, "existing_system", "existing.zip", _make_existing_zip())
+
+    # 上传后直接检索应命中非空
+    hits = rag.retrieve(sid, "订单创建", k=1)
+    assert hits, "上传即索引后应能检索到源码片段"
+    assert "KnownOrder" in hits[0]
+
+    svc.run_parse(sid)
+    svc.confirm_parse(sid)
+    assert svc.get_session(sid).status == "impact_running"
+
+    # 真实驱动 RAG 路径
+    rec = asyncio.run(svc.run_impact(sid, use_rag=True))
+    assert rec.status == "awaiting_impact_confirm"
+    # 核心断言：RAG 检索片段（含 KnownOrder）注入 LLM prompt
+    assert engine.captured is not None
+    assert "KnownOrder" in engine.captured
+    # 摘要标记 rag_enabled
+    import json
+    assert json.loads(rec.impact_summary).get("rag_enabled") is True
+
+
+def test_rag_e2e_use_rag_false_backward_compat(tmp_path):
+    """向后兼容：rag=None 且 use_rag 默认关闭时，不调用 LLM、无 RAG 小节。"""
+    store = SessionStore(db_path=str(tmp_path / "s.db"))
+    engine = FakeEngine()
+    svc = GenesisService(
+        store=store,
+        data_root=str(tmp_path / "data"),
+        engine=engine,
+        rag=None,  # 不启用 RAG
+        use_rag=False,
+    )
+
+    sid = svc.create_session("u1").session_id
+    svc.upload_file(sid, "requirements", "requirements_newdev.xlsx", _sample_req())
+    svc.upload_file(sid, "template", "template_design_ja.docx", _sample_tpl())
+    svc.upload_file(sid, "existing_system", "existing.zip", _make_existing_zip())
+
+    svc.run_parse(sid)
+    svc.confirm_parse(sid)
+
+    rec = asyncio.run(svc.run_impact(sid))  # 默认 use_rag=None → 走确定性路径
+    assert rec.status == "awaiting_impact_confirm"
+    # 向后兼容：确定性路径不调用 LLM（captured 保持 None），prompt 不含 RAG 小节
+    assert engine.captured is None
+    assert _RAG_CONTEXT_TITLE not in (engine.captured or "")
+    # 确定性报告存在
+    assert rec.impact_report_path and Path(rec.impact_report_path).exists()
+
+
+def test_service_rag_lazy_engine_build(tmp_path, monkeypatch):
+    """覆盖 service.py:233-236：构造未传 engine 且 run_impact(use_rag=True) 时懒构建引擎。"""
+    store = SessionStore(db_path=str(tmp_path / "s.db"))
+    rag = ImpactRAG(RagStore(str(tmp_path / "rag.db")), FakeEmbedder())
+    # 注入的懒构建产物：一个会捕获 prompt 的 FakeEngine
+    injected_engine = FakeEngine()
+    monkeypatch.setattr(
+        "genesis.inference.factory.build_inference_engine", lambda: injected_engine
+    )
+    svc = GenesisService(
+        store=store,
+        data_root=str(tmp_path / "data"),
+        rag=rag,
+        use_rag=False,  # 构造时不传 engine、RAG 默认关闭
+    )
+    assert svc.engine is None  # 尚未构建
+
+    sid = svc.create_session("u1").session_id
+    svc.upload_file(sid, "requirements", "requirements_newdev.xlsx", _sample_req())
+    svc.upload_file(sid, "template", "template_design_ja.docx", _sample_tpl())
+    # 上传即索引（D1），existing_system 含 KnownOrder 源码
+    svc.upload_file(sid, "existing_system", "existing.zip", _make_existing_zip())
+    svc.run_parse(sid)
+    svc.confirm_parse(sid)
+    assert svc.get_session(sid).status == "impact_running"
+
+    # 显参开启 RAG → 触发 engine 为 None 的懒构建分支
+    rec = asyncio.run(svc.run_impact(sid, use_rag=True))
+    assert rec.status == "awaiting_impact_confirm"
+    # 懒构建的引擎被注入并实际使用
+    assert svc.engine is injected_engine
+    summary = json.loads(rec.impact_summary)
+    assert summary.get("rag_enabled") is True
+    # 引擎捕获的 prompt 含 RAG 检索注入的 KnownOrder 片段
+    assert injected_engine.captured is not None
+    assert "KnownOrder" in injected_engine.captured
+
+
+def test_http_start_impact_use_rag_e2e(tmp_path):
+    """覆盖 app.py start_impact 异步端点 + _FakeEngine.chat_structured（RAG 路径，HTTP 级）。"""
+    store = SessionStore(db_path=str(tmp_path / "s.db"))
+    rag = ImpactRAG(RagStore(str(tmp_path / "rag.db")), FakeEmbedder())
+    app = create_app(
+        store=store,
+        data_root=str(tmp_path / "data"),
+        engine="fake",  # 触发内部 _FakeEngine（异步 chat_structured）
+        rag=rag,
+    )
+    client = TestClient(app)
+
+    sid = client.post("/api/sessions", json={"user_id": "u1"}).json()["session_id"]
+    # multipart 上传：要件/模板/既有系统
+    client.post(f"/api/sessions/{sid}/files",
+                data={"file_type": "requirements"},
+                files={"file": ("requirements_newdev.xlsx", _sample_req())})
+    client.post(f"/api/sessions/{sid}/files",
+                data={"file_type": "template"},
+                files={"file": ("template_design_ja.docx", _sample_tpl())})
+    client.post(f"/api/sessions/{sid}/files",
+                data={"file_type": "existing_system"},
+                files={"file": ("existing.zip", _make_existing_zip())})
+
+    assert client.post(f"/api/sessions/{sid}/start-parse").status_code == 200
+    # 有既有系统 → impact_running
+    assert client.post(f"/api/sessions/{sid}/confirm-parse").json()["status"] == "impact_running"
+
+    # 异步端点：start-impact?use_rag=True（显参开启 RAG）
+    r = client.post(f"/api/sessions/{sid}/start-impact?use_rag=True")
+    assert r.status_code == 200
+    ir = client.get(f"/api/sessions/{sid}/impact-result").json()
+    # 经 HTTP 真实走到 RAG 路径，摘要标记 rag_enabled
+    assert ir.get("rag_enabled") is True
diff --git a/tests/test_rag_embeddings.py b/tests/test_rag_embeddings.py
new file mode 100644
index 0000000..b1f9770
--- /dev/null
+++ b/tests/test_rag_embeddings.py
@@ -0,0 +1,30 @@
+# tests/test_rag_embeddings.py
+from genesis.rag.embeddings import FakeEmbedder, get_embedder
+
+
+def test_fake_embedder_deterministic():
+    e = FakeEmbedder()
+    a = e.embed(["OrderController 创建订单"])[0]
+    b = e.embed(["OrderController 创建订单"])[0]
+    assert a == b
+
+
+def test_fake_embedder_similar_closer_than_unrelated():
+    e = FakeEmbedder()
+    base = e.embed(["OrderController 处理创建订单请求"])[0]
+    sim = e.embed(["OrderController 保存订单到数据库"])[0]
+    dif = e.embed(["用户登录认证模块"])[0]
+    import math
+
+    def cos(x, y):
+        dot = sum(p * q for p, q in zip(x, y))
+        nx = math.sqrt(sum(p * p for p in x))
+        ny = math.sqrt(sum(q * q for q in y))
+        return dot / (nx * ny or 1.0)
+
+    assert cos(base, sim) > cos(base, dif)
+
+
+def test_get_embedder_fake_engine_returns_fake():
+    e = get_embedder("fake")
+    assert e.__class__.__name__ == "FakeEmbedder"
diff --git a/tests/test_rag_store.py b/tests/test_rag_store.py
new file mode 100644
index 0000000..e350888
--- /dev/null
+++ b/tests/test_rag_store.py
@@ -0,0 +1,61 @@
+import math
+from genesis.rag.store import RagStore
+
+
+def _vec(*ones):
+    v = [0.0] * 8
+    for i in ones:
+        v[i] = 1.0
+    n = math.sqrt(sum(x * x for x in v))
+    return [x / n for x in v]
+
+
+def test_search_returns_most_similar_chunk():
+    s = RagStore(":memory:")
+    s.reset_scope("p1")
+    s.add("p1", ["订单模块处理创建", "用户认证登录"], [_vec(0, 1), _vec(4, 5)])
+    res = s.search("p1", _vec(0, 1), k=1)
+    assert res == ["订单模块处理创建"]
+    # k<=0 健壮性
+    assert s.search("p1", _vec(0, 1), k=0) == []
+    s.close()
+
+
+def test_reset_scope_clears():
+    s = RagStore(":memory:")
+    s.reset_scope("p1")
+    s.add("p1", ["a"], [_vec(0)])
+    s.reset_scope("p1")
+    assert s.search("p1", _vec(0), k=3) == []
+    # chunks 与 embeddings 长度不一致应抛 ValueError
+    try:
+        import pytest
+        with pytest.raises(ValueError):
+            s.add("p1", ["a", "b"], [_vec(0)])
+    finally:
+        s.close()
+
+
+def test_concurrent_add_and_search_no_crash():
+    import threading
+    s = RagStore(":memory:")
+    s.reset_scope("p1")
+
+    def worker(i):
+        # 每个 worker 线程内交替执行 add 与 search，让读写真正并发跨线程运行
+        for j in range(5):
+            s.add("p1", [f"chunk-{i}-{j}"], [_vec(i % 8)])
+            res = s.search("p1", _vec(i % 8), k=3)
+            assert all(isinstance(r, str) for r in res)
+
+    try:
+        threads = [threading.Thread(target=worker, args=(i,)) for i in range(8)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+        res = s.search("p1", _vec(0), k=3)
+        assert len(res) <= 3
+        assert all(isinstance(r, str) for r in res)
+    finally:
+        s.close()
diff --git a/tests/test_server_service.py b/tests/test_server_service.py
index e9215a1..c2814c3 100644
--- a/tests/test_server_service.py
+++ b/tests/test_server_service.py
@@ -7,6 +7,7 @@ from __future__ import annotations
 from pathlib import Path
 from types import SimpleNamespace
 
+import asyncio
 import pytest
 
 from genesis.server.store import SessionStore, ProjectsStore
@@ -248,7 +249,7 @@ def test_existing_system_zip_triggers_impact_flow(tmp_path):
     svc.confirm_parse(s.session_id)
     assert svc.get_session(s.session_id).status == "impact_running"
 
-    svc.run_impact(s.session_id)
+    asyncio.run(svc.run_impact(s.session_id))
     got = svc.get_session(s.session_id)
     assert got.status == "awaiting_impact_confirm"
     assert got.impact_summary
@@ -269,7 +270,7 @@ def test_impact_state_guard(svc):
     svc.confirm_parse(s.session_id)
     # 无既有系统 → writing，start-impact 应报错
     with pytest.raises(ServiceStepError):
-        svc.run_impact(s.session_id)
+        asyncio.run(svc.run_impact(s.session_id))
 
 
 def test_qa_requires_generated(svc):