feat(review): 审查结论改为结构化 JSON，移除二次 LLM 抽取

- checklist.py：系统提示加入结构化输出契约（只输出 {summary, issues[]}，
  引用 handle 必须真实存在、不得编造）
- review.py：review_frame 返回 {summary, issues, raw}；仅在「不再请求工具」的回合
  解析结论，中间工具回合的 content 永不解析；强制收口那次 chat 不传 tools
- report.py：删除 extract_issues 与 _EXTRACT_SYSTEM（不再需要第二次 LLM 调用）；
  新增 format_finding（用 .get，顺带修复缺 frame 键 KeyError）；save_report 的
  issues 省略时从 findings 拍平
- __main__.py：主流程改为 确定性检查 → review_frame → build_finding（合并+校验），
  issues 由 flatten_issues 派生

顺带修复既有 gap：summarize 硬下标 KeyError、extract_issues 单行围栏解析失败。

tests/test_review.py

@@ -111,11 +111,12 @@ def test_readonly_empty_response_marker():
 # ---------------------------------------------------------------------------
 #  review_frame
 # ---------------------------------------------------------------------------
-def test_review_frame_returns_text_when_no_tools():
+def test_review_frame_returns_summary_when_no_tools():
     llm = FakeLlmClient(script=[llm_text("结论A")])
     ctx = make_ctx(client=FakeMcpClient(), llm=llm)
     out = review_frame(ctx, make_evidence(), "系统提示", log=lambda *a: None)
-    assert out == "结论A"
+    assert out["summary"] == "结论A"  # 非 JSON → 降级为纯文本 summary
+    assert out["issues"] == []
     assert len(llm.calls) == 1
     assert llm.calls[0]["tools"] is not None  # 传了只读工具 schema
 
@@ -147,7 +148,7 @@ def test_review_frame_runs_tool_then_concludes():
     client = FakeMcpClient(responses={"query_entities": ok_text({"total": 1})})
     ctx = make_ctx(client=client, llm=llm)
     out = review_frame(ctx, make_evidence(), "sys", log=lambda *a: None)
-    assert out == "结论B"
+    assert out["summary"] == "结论B"
     assert len(llm.calls) == 2
     assert client.called_names() == ["query_entities"]
 
@@ -179,7 +180,7 @@ def test_review_frame_force_closes_at_iteration_limit():
     )
     ctx = make_ctx(client=FakeMcpClient(), llm=llm, max_iters=1)
     out = review_frame(ctx, make_evidence(), "sys", log=lambda *a: None)
-    assert out == "收口结论"
+    assert out["summary"] == "收口结论"
     last_msg = llm.calls[-1]["messages"][-1]
     assert last_msg["role"] == "user"
     assert "上限" in last_msg["content"]
@@ -189,7 +190,7 @@ def test_review_frame_with_zero_iters_forces_immediate_close():
     llm = FakeLlmClient(script=[llm_text("直接结论")])
     ctx = make_ctx(client=FakeMcpClient(), llm=llm, max_iters=0)
     out = review_frame(ctx, make_evidence(), "sys", log=lambda *a: None)
-    assert out == "直接结论"
+    assert out["summary"] == "直接结论"
     assert len(llm.calls) == 1
 
 
@@ -207,3 +208,38 @@ def test_review_frame_payload_is_json_serializable():
     review_frame(ctx, make_evidence(), "sys", log=lambda *a: None)
     text = llm.calls[0]["messages"][1]["content"][0]["text"]
     json.loads(text.split("：\n", 1)[1])  # 不抛异常即通过
+
+
+def test_review_frame_parses_structured_json_conclusion():
+    text = (
+        '{"summary": "整体尚可", "issues": ['
+        '{"category": "几何", "severity": "medium", "message": "零长度", "handle": "A1"}]}'
+    )
+    llm = FakeLlmClient(script=[llm_text(text)])
+    ctx = make_ctx(client=FakeMcpClient(), llm=llm)
+    out = review_frame(ctx, make_evidence(), "sys", log=lambda *a: None)
+    assert out["summary"] == "整体尚可"
+    assert out["issues"] == [
+        {"category": "几何", "severity": "medium", "message": "零长度", "handle": "A1"}
+    ]
+
+
+def test_review_frame_parses_fenced_json():
+    llm = FakeLlmClient(script=[llm_text('```json\n{"summary": "s", "issues": []}\n```')])
+    ctx = make_ctx(client=FakeMcpClient(), llm=llm)
+    out = review_frame(ctx, make_evidence(), "sys", log=lambda *a: None)
+    assert out["summary"] == "s"
+    assert out["issues"] == []
+
+
+def test_review_frame_intermediate_tool_turn_json_not_parsed():
+    # 中间工具回合的 content 里即使塞了 JSON，也不能被当成最终结论
+    intermediate = '{"summary": "这不是最终结论", "issues": [{"message": "x"}]}'
+    llm = FakeLlmClient(script=[
+        llm_calls([("query_entities", {})], content=intermediate),
+        llm_text('{"summary": "最终结论", "issues": []}'),
+    ])
+    ctx = make_ctx(client=FakeMcpClient(), llm=llm)
+    out = review_frame(ctx, make_evidence(), "sys", log=lambda *a: None)
+    assert out["summary"] == "最终结论"
+    assert out["issues"] == []