fix: tighten AST check to module-level only

The original tree-wide ast.walk() would match registry.register() calls
inside functions too. Restrict to top-level ast.Expr statements so helper
modules that call registry.register() inside a function are never picked
up as tool modules.

tools/registry.py

@@ -25,26 +25,32 @@ from typing import Callable, Dict, List, Optional, Set
 logger = logging.getLogger(__name__)
 
 
+def _is_registry_register_call(node: ast.AST) -> bool:
+    """Return True when *node* is a ``registry.register(...)`` call expression."""
+    if not isinstance(node, ast.Expr) or not isinstance(node.value, ast.Call):
+        return False
+    func = node.value.func
+    return (
+        isinstance(func, ast.Attribute)
+        and func.attr == "register"
+        and isinstance(func.value, ast.Name)
+        and func.value.id == "registry"
+    )
+
+
 def _module_registers_tools(module_path: Path) -> bool:
-    """Return True when the module contains a direct ``registry.register(...)`` call."""
+    """Return True when the module contains a top-level ``registry.register(...)`` call.
+
+    Only inspects module-body statements so that helper modules which happen
+    to call ``registry.register()`` inside a function are not picked up.
+    """
     try:
         source = module_path.read_text(encoding="utf-8")
         tree = ast.parse(source, filename=str(module_path))
     except (OSError, SyntaxError):
         return False
 
-    for node in ast.walk(tree):
-        if not isinstance(node, ast.Call):
-            continue
-        func = node.func
-        if (
-            isinstance(func, ast.Attribute)
-            and func.attr == "register"
-            and isinstance(func.value, ast.Name)
-            and func.value.id == "registry"
-        ):
-            return True
-    return False
+    return any(_is_registry_register_call(stmt) for stmt in tree.body)
 
 
 def discover_builtin_tools(tools_dir: Optional[Path] = None) -> List[str]: