Calling node.place(field_1) after field_2.from_numpy() raises RuntimeError "dense node must have at least one child."

[sunjp704]

Describe the bug
Calling node.place(field_1) after field_2.from_numpy() raises RuntimeError "dense node must have at least one child."

To Reproduce

import numpy as np
import taichi as ti

ti.init(arch=ti.cuda)

node= ti.root.dense(ti.ij, (3, 2))
field_1 = ti.field(dtype=float)
# node.place(field_1) # moving this line to the end causes problem

field_2 = ti.field(dtype=float, shape=(3,))
field_2.from_numpy(np.array([1, 2, 3]))

node.place(field_1)

field_1 and field_2 are supposed to be independent of each other. But if I call node.place(field_1) after field_2.from_numpy(), it raises RuntimeError: [snode_tree.cpp:taichi::lang::SNodeTree::check_tree_validity@26] dense node must have at least one child.

Log/Screenshots

(taichi) PS D:\codes\TaichiTest> & C:\Programs\miniforge3\envs\taichi\python.exe d:/codes/TaichiTest/tests/test.py
[Taichi] version 1.7.4, llvm 15.0.1, commit b4b956fd, win, python 3.13.12
[Taichi] Starting on arch=cuda
[E 05/21/26 13:56:08.546 21824] [snode_tree.cpp:taichi::lang::SNodeTree::check_tree_validity@26] dense node must have at least one child.


Traceback (most recent call last):
  File "d:\codes\TaichiTest\tests\test.py", line 10, in <module>
    field_2.from_numpy(np.array([1, 2, 3]))
    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\util.py", line 351, in wrapped
    return func(*args, **kwargs)
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\field.py", line 357, in from_numpy
    self._from_external_arr(arr)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\util.py", line 351, in wrapped
    return func(*args, **kwargs)
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\field.py", line 347, in _from_external_arr
    ext_arr_to_tensor(arr, self)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\kernel_impl.py", line 1113, in wrapped
    return primal(*args, **kwargs)
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\kernel_impl.py", line 1043, in __call__
    key = self.ensure_compiled(*args)
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\kernel_impl.py", line 1011, in ensure_compiled
    self.materialize(key=key, args=args, arg_features=arg_features)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\kernel_impl.py", line 637, in materialize
    self.runtime.materialize()
    ~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\impl.py", line 471, in materialize
    self.materialize_root_fb(not self.materialized)
    ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\lang\impl.py", line 406, in materialize_root_fb
    root.finalize(raise_warning=not is_first_call)
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\_snode\fields_builder.py", line 170, in finalize
    return self._finalize(raise_warning, compile_only=False)
           ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Programs\miniforge3\envs\taichi\Lib\site-packages\taichi\_snode\fields_builder.py", line 182, in _finalize
    return SNodeTree(_ti_core.finalize_snode_tree(_snode_registry, self.ptr, impl.get_runtime().prog, compile_only))
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: [snode_tree.cpp:taichi::lang::SNodeTree::check_tree_validity@26] dense node must have at least one child.