fix(gen): callable[[]]（省略返回类型）按默认 int(i32) 注册函数指针签名，修间接调用签名缺失 fail-fast

App/lib/core/Gen/Type/TypeGenErr.vp

@@ -102,10 +102,15 @@ novirtual class TypeGenErr(TypeGenBase.TypeGenBase):
         # The subscript test uses TypeGenResolve as the single source of truth (the t.Callable
         # Attribute form is equivalent to the bare-name callable / Callable forms)
         if self.Gen.TypeGenResolve._IsCallableSubscriptValue(sub_cr.value) == 0: return None
-        # slice must be Tuple(elts=[args_list, ret_node])
+        # slice must be Tuple(elts=[args_list, ret_node]); the one-element form
+        # `callable[[A, B]]` omits the return type and means the default int (i32) — the same
+        # degradation a missing annotation gets elsewhere. It must still register, otherwise the
+        # indirect call fails fast with "Return type ... is not registered".
         if sub_cr.slice is None or sub_cr.slice.kind() != ast.ASTKind.Tuple: return None
         tp_cr: ast.Tuple* = ast.Tuple*(sub_cr.slice)
-        if tp_cr.elts is None or len(tp_cr.elts) != 2: return None
+        if tp_cr.elts is None: return None
+        if len(tp_cr.elts) == 1: return mlirlite.Int32(pool)
+        if len(tp_cr.elts) != 2: return None
         ret_node_cr: ast.AST* = tp_cr.elts.get(1)
         if ret_node_cr is None: return None
         return self.Gen.TypeGenResolve.resolve_annotation_type(pool, ret_node_cr, imported_modules, from_imports, trans, 0)