feat(impact): Impact Agent MVP —— 变更点定位 + 影响调查书（追加改修场景）

- 门控：用户提供 existing_system 路径 → 进入影响调查；未提供 → 原流程不变
- CodeParser 解析 Java（@RestController/@Service/@Entity/@TableName）+ ExistingSystemExplorer 组装
- ImpactAgent 变更点定位（变更区分×既存対応 确定性比对，无 LLM）→ ImpactReport（JSON 可下载）
- 影响调查结果作为 Writer 生成概要设计书的主上下文（{{impact}}，无专用影响章）
- source_aggregator 解除 existing_system=None 硬编码
- 既有系统样本 sunOnly/stock-trade-system（无 LICENSE，仅测试输入，保留来源标注）
- 新造股票交易域追加改修样本 要件定義_追加改修_股票.xlsx（对齐 sunOnly 真实类名）
- 全量 351 passed / 99.27% 覆盖；门禁 PASS（16 要素：新规5/変更8/削除3/未受影响50）

tests/test_phase5_writer_orchestrator.py

@@ -2,13 +2,20 @@ import pytest
 from types import SimpleNamespace
 from docx import Document
 
-from genesis.data_models import ParsedTemplate, ChapterMarker
+from genesis.data_models import (
+    ControllerInfo, EntityInfo, ExistingSystemInfo, ImpactReport, ParsedTemplate,
+    ChapterMarker, ServiceInfo,
+)
 from genesis.writer.orchestrator import WriteOrchestrator
 from genesis.writer.models import ChapterContent
 
 
 class FakeEngine:
+    def __init__(self):
+        self.last_variables = None
+
     def chat_structured(self, *, session_id, prompt, variables, schema, retry_count=2):
+        self.last_variables = variables
         # 返回一个固定章节内容（title + 一个段落块）
         return SimpleNamespace(
             data={"title": variables["title"], "blocks": [{"type": "paragraph", "text": "自动生成的内容"}]},
@@ -108,3 +115,90 @@ def test_generate_warns_on_unanchored_heading(tmp_path, caplog):
             template_path=str(tpl),
         )
     assert any("附録" in r.message for r in caplog.records)
+
+
+# ---------- Impact Agent MVP：影响调查结果作为生成主上下文（2026-08-23） ----------
+
+def _ss_with_existing(template_path):
+    from genesis.data_models import CellValue, ExcelTable, Provenance, SheetType
+    parsed = ParsedTemplate(
+        file_name=template_path,
+        sections=[
+            ChapterMarker(type="heading", name="はじめに", level=1),
+            ChapterMarker(type="placeholder", name="section:introduction", level=0),
+        ],
+        placeholders={},
+        styles={"defined": ["Heading 1"], "used": ["Heading 1"]},
+    )
+    existing = ExistingSystemInfo(
+        controller_layer=[ControllerInfo("OrderController", "OrderController", "OrderController.java",
+                                         "/trade/order", [], "trade-order/OrderController.java")],
+        service_layer=[],
+        entity_layer=[EntityInfo("OrderDO", "OrderDO", "OrderDO.java", "trade_order", ["id"], "trade-order/OrderDO.java")],
+        api_endpoints=[],
+        source_path="samples/existing-system",
+    )
+    headers = ["機能ID", "機能名", "変更区分", "既存対応"]
+    rows = [{
+        "機能ID": CellValue("F002", Provenance("f.xlsx", "機能一覧", 3, "A", "機能ID")),
+        "機能名": CellValue("订单状态查询扩展", Provenance("f.xlsx", "機能一覧", 3, "B", "機能名")),
+        "変更区分": CellValue("変更", Provenance("f.xlsx", "機能一覧", 3, "G", "変更区分")),
+        "既存対応": CellValue("OrderController", Provenance("f.xlsx", "機能一覧", 3, "H", "既存対応")),
+    }]
+    tables = [ExcelTable(name="機能一覧", detected_type=SheetType.FUNCTION, extraction_method="openpyxl",
+                         headers=headers, rows=rows)]
+    return SimpleNamespace(template=parsed, existing_system=existing, tables=tables,
+                           impact_report=None)
+
+
+def test_generate_auto_runs_impact_when_existing_system(tmp_path):
+    """门控：existing_system 非 None 且未显式传 impact_report → 自动跑影响调查，注入生成上下文。"""
+    tpl = tmp_path / "tpl.docx"
+    out = tmp_path / "out.docx"
+    _make_template(str(tpl))
+    engine = FakeEngine()
+    WriteOrchestrator().generate(
+        _ss_with_existing(str(tpl)), str(out),
+        samples_dir="nonexistent_dir_xyz", engine=engine,
+    )
+    impact = engine.last_variables["impact"]
+    assert "project_type=enhancement" in impact
+    assert "OrderController" in impact
+
+
+def test_generate_without_existing_system_impact_empty(tmp_path):
+    tpl = tmp_path / "tpl.docx"
+    out = tmp_path / "out.docx"
+    _make_template(str(tpl))
+    engine = FakeEngine()
+    WriteOrchestrator().generate(
+        _ss(str(tpl)), str(out),
+        samples_dir="nonexistent_dir_xyz", engine=engine,
+    )
+    assert engine.last_variables["impact"] == ""
+
+
+def test_generate_explicit_impact_report_used(tmp_path):
+    from genesis.data_models import ChangeAnalysis, ChangeElement, ChangeType
+    tpl = tmp_path / "tpl.docx"
+    out = tmp_path / "out.docx"
+    _make_template(str(tpl))
+    ca = ChangeAnalysis(project_type="enhancement", new_elements=[], modified_elements=[],
+                        deleted_elements=[], unchanged_elements=[], warnings=[])
+    report = ImpactReport(metadata={"version": "v1"}, change_analysis=ca, summary={"new": 0})
+    engine = FakeEngine()
+    ss = _ss_with_existing(str(tpl))
+    WriteOrchestrator().generate(ss, str(out), samples_dir="nonexistent_dir_xyz",
+                                 engine=engine, impact_report=report)
+    assert engine.last_variables["impact"] != ""
+    # 显式传入时也回填 structured_source，便于 QA/日志读取
+    assert ss.impact_report is report
+
+
+def test_generate_missing_template_path_raises(tmp_path):
+    parsed = ParsedTemplate(file_name=None, sections=[], placeholders={}, styles={"used": []})
+    with pytest.raises(ValueError, match="template_path"):
+        WriteOrchestrator().generate(
+            SimpleNamespace(template=parsed), str(tmp_path / "out.docx"),
+            samples_dir="nonexistent_dir_xyz", engine=FakeEngine(),
+        )