SpatialData repr breaks when Dask auto-partitions Parquet points

[enric-bazz]

Hi,
I'm encountering an issue when calling repr(sdata) which fails during the self-contained check for points elements backed by a Parquet file with the error:

AttributeError: 'list' object has no attribute 'values'

The failure originates in
_search_for_backing_files_recursively()
where the code assumes that each parquet-read task in the Dask graph has a dict in task.args[0] and therefore calls:

v.args[0].values()

However, when dask.dataframe.read_parquet() performs automatic partition aggregation, controlled by split_row_groups='infer' (default), task.args[0] can become a list of row-group dicts instead of a single dict.

Reproduce

To reproduce the error, first trigger Dask’s autopartitioning by forcing a DataFrame into a single partition, writing it to a Parquet file and reading it back with default read_parquet settings. Inspecting the graph reveals the list-of-dicts structure that breaks SpatialData. To trigger the original error, parse the DataFrame with PointsModel, build a SpatialData object, write it to a Zarr store (the error does not occur if unbacked), and finally call repr(sdata). The pseudocode is the following:

import dask.dataframe as dd
from spatialdata._core.points import PointsModel
from spatialdata._core.spatialdata import SpatialData

# 1. Create or load a Dask DataFrame
df = dd.from_pandas(some_pandas_df, npartitions=4)

# 2. Force a single partition
df_one_part = df.repartition(npartitions=1)

# 3. Write single-partition Parquet
df_one_part.to_parquet("example_points.parquet")

# 4. Read Parquet back
df_read = dd.read_parquet("example_points.parquet")

# 5. Inspect graph (optional)
print(df_read.dask)  # shows list-of-dicts if autopartitioning changed structure

# 6. Parse with PointsModel
points = PointsModel.parse(df_read)

# 7. Build SpatialData object
sdata = SpatialData(points=points)

# 8. Write to Zarr store (error triggers only when sdata.is_backed() == True)
sdata.write("example.zarr")

# 9. Trigger error with repr
print(repr(sdata))

[LucaMarconato]

Thanks for reporting! Related to #1077. Looping in also @melonora.