fix(writer): 章节级数据注入 + 修复 prompt 从未渲染的关键缺陷

- models: CHAPTER_SHEET_TYPES/CHAPTER_IMPACT_ELEMENT 章节→数据映射（design §6.8 ①）
- models: _format_chapter_data 按章定向渲染 ExcelTable 为 Markdown；GENERIC 自由記述作通用背景
- models: _format_impact 支持按 ElementType 过滤（章节级影响上下文）
- writer_agent: {{source}}(全量repr) → {{data}}(章节数据)；新增【主题约束】
- writer_agent: 关键修复——真实 PromptRegistry.get 返回模板字符串，
  引擎对 str 不做变量渲染，LLM 实际收到的是 {{占位符}} 原文；
  _resolve_prompt 统一包装为 Prompt 对象保证渲染
- 真实试运行验证：13 章主题全部正确、引用影响调查数据、语言漂移消除

tests/test_phase5_context_builder.py

@@ -45,3 +45,43 @@ def test_build_contexts_carries_impact_report():
     ctxs = build_contexts(ss, samples_dir="nonexistent_dir_xyz")
     assert ctxs[0].impact_report is report
     assert "project_type" in ctxs[0].to_vars()["impact"] or ctxs[0].to_vars()["impact"] != ""
+
+
+def test_build_contexts_vars_data_scoped_per_chapter():
+    """集成：多章模板 + FUNCTION/DB 表 → 各章 to_vars()['data'] 按章节定向。"""
+    from genesis.data_models import (
+        CellValue, ExcelTable, Provenance, SheetType, StructuredSource,
+    )
+    template = ParsedTemplate(
+        file_name="t.docx",
+        sections=[
+            ChapterMarker(type="heading", name="機能一覧", level=1),
+            ChapterMarker(type="placeholder", name="section:function_list", level=0),
+            ChapterMarker(type="heading", name="DB設計", level=1),
+            ChapterMarker(type="placeholder", name="section:db_design", level=0),
+        ],
+        placeholders={},
+        styles={"used": ["Heading1"]},
+    )
+
+    def cell(v):
+        return CellValue(value=v, provenance=Provenance("f.xlsx", "s", 1, "A", "列"))
+
+    ss = StructuredSource(
+        tables=[
+            ExcelTable("機能一覧", SheetType.FUNCTION, "openpyxl",
+                       ["機能ID", "機能名"],
+                       [{"機能ID": cell("F001"), "機能名": cell("止损风控")}]),
+            ExcelTable("DB定義", SheetType.DATABASE, "openpyxl",
+                       ["テーブルID", "テーブル名"],
+                       [{"テーブルID": cell("T001"), "テーブル名": cell("trade_order")}]),
+        ],
+        template=template, rule_docs=[], image_analyses=[],
+        existing_system=None, comments=[],
+    )
+    ctxs = build_contexts(ss, samples_dir="nonexistent_dir_xyz")
+    by_id = {c.chapter_id: c for c in ctxs}
+    fn = by_id["function_list"].to_vars()["data"]
+    db = by_id["db_design"].to_vars()["data"]
+    assert "F001" in fn and "trade_order" not in fn
+    assert "T001" in db and "止损风控" not in db