落地 12.2 二十个用例目录：toml + .st + 期望表。

- tests/cases/ 01~20：13 正例 / 6 负例 / 1 运行时故障
- 负例冻结报错类别：非 GVL 写全局、同名全局、io.var 未声明、FUNCTION 写全局、未声明实例、循环调用
- tests/README 补充用例清单与点亮节奏

tests/cases/20_line1/project.toml

@@ -0,0 +1,28 @@
+[project]
+name = "line1"
+entry = "program MAIN"
+cycle_limit = 100000
+dt_ms = 10
+
+[files]
+st = ["globals.st", "motor.st", "main.st"]
+
+# 全工程只允许这一处出现 VAR_GLOBAL（第一版：单个文件）
+[gvl]
+file = "globals.st"
+
+# 可选：I/O 绑定。不创造变量，var 必须已在 GVL 里声明
+[[io.input]]
+var = "EmergencyStop"
+channel = 0
+bit = 2
+
+[[io.input]]
+var = "I0_0"
+channel = 0
+bit = 0
+
+[[io.output]]
+var = "Q0_0"
+channel = 0
+bit = 0