test: 补齐覆盖率工具（pytest-cov，fail_under=90，基线 96.67%）

pyproject.toml

@@ -16,10 +16,25 @@ dependencies = [
 ]
 
 [project.optional-dependencies]
-dev = ["pytest>=8.0"]
+dev = ["pytest>=8.0", "pytest-cov>=7.0"]
 
 [tool.setuptools.packages.find]
 where = ["src"]
 
 [tool.pytest.ini_options]
-testpaths = ["tests"]
+testpaths = ["tests"]
+addopts = "--cov=genesis --cov-report=term-missing"
+
+[tool.coverage.run]
+# 仅统计 src/genesis 业务代码（不含 tests 自身）
+source = ["genesis"]
+# 测量分支覆盖
+branch = true
+
+[tool.coverage.report]
+# 覆盖率门槛：低于该值 pytest 失败（红线，防止回归）
+fail_under = 90
+# 跳过 __init__.py 等空文件干扰
+skip_empty = true
+# 按语句总数降序展示
+sort = "miss"