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_data_models.py

@@ -1,8 +1,9 @@
 from dataclasses import asdict
 
 from genesis.data_models import (
-    CellComment, CellFormatting, CellValue, Confidence, ElementType,
-    ExcelTable, ExtractionMethod, ImageAnalysis, ParsedTemplate, Provenance,
+    CellComment, CellFormatting, CellValue, ChangeAnalysis, ChangeElement,
+    ChangeType, Confidence, ElementType, ExcelTable, ExtractionMethod,
+    ImageAnalysis, ImpactReport, ImpactWarning, ParsedTemplate, Provenance,
     RelationType, RuleDocument, SheetType, StructuredSource,
 )
 
@@ -75,3 +76,56 @@ def test_asdict_serializable():
     prov = Provenance(file_name="f.xlsx", sheet_name="S", row=1, column="A", column_header="h")
     d = asdict(CellValue(value=1, provenance=prov))
     assert d["provenance"]["row"] == 1
+
+
+# ---------- Impact Agent MVP 数据模型（2026-08-23） ----------
+
+def test_changetype_members():
+    assert ChangeType.NEW.value == "新規"
+    assert ChangeType.MODIFIED.value == "変更"
+    assert ChangeType.DELETED.value == "削除"
+    assert ChangeType.UNCHANGED.value == "不变"
+
+
+def test_change_element_defaults():
+    el = ChangeElement(element_id="F001", element_type="機能", name="止损风控", change_type=ChangeType.NEW)
+    assert el.existing_mapping == []
+    assert el.impacted_existing == []
+    assert el.evidence == ""
+    assert el.status == "ok"
+
+
+def test_change_analysis_holds_lists():
+    ca = ChangeAnalysis(
+        project_type="enhancement",
+        new_elements=[ChangeElement("F001", "機能", "止损风控", ChangeType.NEW)],
+        modified_elements=[],
+        deleted_elements=[],
+        unchanged_elements=[],
+        warnings=[ImpactWarning(element_id="F002", issue="无法定位修改对象")],
+    )
+    assert ca.project_type == "enhancement"
+    assert ca.new_elements[0].element_id == "F001"
+    assert ca.warnings[0].issue == "无法定位修改对象"
+
+
+def test_impact_report_defaults():
+    report = ImpactReport(metadata={"version": "v1"})
+    assert report.change_analysis is None
+    assert report.summary == {}
+
+
+def test_impact_report_holds_analysis():
+    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})
+    assert report.change_analysis.project_type == "enhancement"
+    assert report.summary["new"] == 0
+
+
+def test_structured_source_impact_report_default_none():
+    """StructuredSource 新增 impact_report 字段，缺省 None（门控未提供时保持 None）。"""
+    source = StructuredSource(
+        tables=[], template=None, rule_docs=[], image_analyses=[], existing_system=None, comments=[],
+    )
+    assert source.impact_report is None