diff --git a/pybot/pybot/__init__.py b/pybot/pybot/__init__.py
index d732b84..d7be04d 100644
--- a/pybot/pybot/__init__.py
+++ b/pybot/pybot/__init__.py
@@ -25,3 +25,4 @@ from .parser import (          # noqa: F401
     to_int,
 )
 from .robot import RobotStruct  # noqa: F401
+from .plugin import PluginNotFound, PluginProtocolError, PluginVar  # noqa: F401
diff --git a/pybot/pybot/hardvars.py b/pybot/pybot/hardvars.py
index b25a31f..3f236a7 100644
--- a/pybot/pybot/hardvars.py
+++ b/pybot/pybot/hardvars.py
@@ -114,7 +114,12 @@ class MPU6050Var(HardwareVar):
         addr = get_mt(matrix, i, matrix.index_of_col(0, "addr"))
         log.info("Create a MPU6050_BIND HVar: %s, use i2c interf: %s, "
                  "i2c addr: %s", name, i2c_name, addr)
-        fd = M[i2c_name].play({})["fd"]     # 引用 I2C 变量取 fd
+        i2c_var = M[i2c_name]
+        if not isinstance(i2c_var, I2CVar):
+            raise TypeError(
+                f"@MPU6050_BIND '{name}' references '{i2c_name}', "
+                f"but it is a {type(i2c_var).__name__}, not an I2CVar")
+        fd = i2c_var.play({})["fd"]
         return cls(name, MPU6050(fd, to_int(addr)))
 
 
diff --git a/pybot/pybot/hd/kalman.py b/pybot/pybot/hd/kalman.py
index b3001a4..f353d60 100644
--- a/pybot/pybot/hd/kalman.py
+++ b/pybot/pybot/hd/kalman.py
@@ -21,7 +21,7 @@ class Kalman:
     def filter(self, dat):
         x_mid = self.a * self.x_last            # (1) x(k|k-1) = A*X(k-1|k-1)
         p_mid = self.a * self.p_last + self.q   # (2) p(k|k-1) = A*p(k-1|k-1)*A'+Q
-        kg = p_mid / (p_mid + self.r)           # (4) kg(k) = p(k|k-1)/(p(k|k-1)+R)
+        kg = p_mid / max(p_mid + self.r, 1e-10)   # (4) kg(k) = p(k|k-1)/(p(k|k-1)+R)
         x_now = x_mid + kg * (dat - x_mid)      # (3) x(k|k) = X(k|k-1)+kg*(Z(k)-X(k|k-1))
         p_now = (1.0 - kg) * p_mid              # (5) p(k|k) = (1-kg)*P(k|k-1)
         self.p_last = p_now
diff --git a/pybot/pybot/plugin.py b/pybot/pybot/plugin.py
index 9f5b00e..1e3c931 100644
--- a/pybot/pybot/plugin.py
+++ b/pybot/pybot/plugin.py
@@ -37,6 +37,17 @@ class PluginNotFound(Exception):
         self.searched = searched
 
 
+class PluginProtocolError(Exception):
+    """插件缺少 build / call / destroy 之一"""
+
+    def __init__(self, name, path, missing):
+        super().__init__(
+            f"plugin '{name}' at {path} missing function: {missing}(ctx)")
+        self.name = name
+        self.path = path
+        self.missing = missing
+
+
 def search_dirs():
     """插件搜索目录（按优先级）：$PYBOT_MODULES_PATH → 包内置 → cwd"""
     dirs = []
@@ -68,9 +79,7 @@ def load_module(name):
     spec.loader.exec_module(module)
     for fn in ("build", "call", "destroy"):
         if not callable(getattr(module, fn, None)):
-            raise PluginNotFound(
-                name, [path]) from ValueError(
-                f"plugin '{name}' missing function {fn}(ctx)")
+            raise PluginProtocolError(name, path, fn)
     log.debug("loaded plugin %s from %s", name, path)
     return module
 
diff --git a/pybot/tests/test_cli.py b/pybot/tests/test_cli.py
new file mode 100644
index 0000000..459ea46
--- /dev/null
+++ b/pybot/tests/test_cli.py
@@ -0,0 +1,49 @@
+"""CLI 端到端测试：--dry-run / --test roundtrip / stdin 输入"""
+
+import io
+import sys
+
+from tests.conftest import SCRIPTS_DIR
+
+from pybot.main import main
+
+
+def test_stdin_input(monkeypatch):
+    """stdin 输入（模拟 cat script | pybot）"""
+    src = (SCRIPTS_DIR / "std.mt").read_text(encoding="utf-8")
+    monkeypatch.setattr(sys, "stdin", io.StringIO(src))
+    monkeypatch.setattr(sys, "argv", ["pybot", "--dry-run"])
+    # 验证不抛异常且返回 0
+    assert main(["--dry-run"]) == 0
+
+
+def test_cli_help():
+    """--help 返回 0"""
+    try:
+        main(["--help"])
+    except SystemExit as e:
+        assert e.code == 0
+
+
+def test_test_roundtrip(tmp_path):
+    """--test roundtrip in.mt out.mt 往返"""
+    src = (SCRIPTS_DIR / "std.mt").read_text(encoding="utf-8")
+    infile = tmp_path / "in.mt"
+    infile.write_text(src, encoding="utf-8")
+    outfile = tmp_path / "out.mt"
+    assert main(["--test", "roundtrip", str(infile), str(outfile)]) == 0
+    # 输出可被再次解析
+    from pybot.parser import MatrixParser
+    parser = MatrixParser(outfile.read_text(encoding="utf-8"))
+    blocks = []
+    while True:
+        obj = parser.parse()
+        if obj is None:
+            break
+        blocks.append(obj)
+    assert len(blocks) == 7      # std.mt 含 7 个 @块
+
+
+def test_test_unknown_mode():
+    """未知 --test 模式返回 2"""
+    assert main(["--test", "unknown", "/dev/null", "/dev/null"]) == 2
diff --git a/pybot/tests/test_plugin.py b/pybot/tests/test_plugin.py
index 211967c..f0a01bf 100644
--- a/pybot/tests/test_plugin.py
+++ b/pybot/tests/test_plugin.py
@@ -36,7 +36,7 @@ def test_missing_protocol_function(tmp_path, monkeypatch):
     (tmp_path / "Broken.py").write_text(
         "def build(ctx): return {}\n", encoding="utf-8")
     monkeypatch.setenv("PYBOT_MODULES_PATH", str(tmp_path))
-    with pytest.raises(plugin.PluginNotFound):
+    with pytest.raises(plugin.PluginProtocolError):
         plugin.load_module("Broken")