Updating DataArray attributes in a Zarr archive does not work as for Dataset

What happened?

When using the new functionality of calling to_zarr on DataArrays, I've noticed that the attributes are not updated and can only be set once, on initial archive creation. In our case, we are performing sequential writes to the Zarr regions and also want to update attributes. Regular Zarr API allows updating metadata and it also works with Datasets, so we suspect it's an issue with DataArrays. In fact, when calling to_zarr, the DataArray is converted to a Dataset, but when we check it, it does not have its attributes, as they live inside the nested array.

What did you expect to happen?

I would like to update attributes in the same manner as with plain Zarr or with Datasets. Currently, we have to resort to modifying the .zmetadata JSON and consider this dangerous and hacky.

Minimal Complete Verifiable Example

import xarray as xr

ds_path = "ds"
xr.Dataset().assign_attrs(a=1).to_zarr(ds_path, mode="w")
xr.open_dataset(ds_path, engine="zarr").assign_attrs(b=2).to_zarr(ds_path, mode="a")

da_path = "da"
xr.DataArray().assign_attrs(a=1).to_zarr(da_path, mode="w")
xr.open_dataarray(da_path, engine="zarr").assign_attrs(b=2).to_zarr(da_path, mode="a")

print(xr.open_dataset(ds_path, engine="zarr").attrs == xr.open_dataarray(da_path, engine="zarr").attrs)

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

No response

Anything else we need to know?

No response

Environment

Start with the minimal example using DataArray.to_zarr and compare its behavior with Dataset.to_zarr. Trace the DataArray-to-Dataset conversion and Zarr metadata update path; the issue is done when sequential DataArray writes update attributes like Dataset writes do, with a regression test covering the example.