UxDataArray.subset.bounding_box() on edge-centered data crashes with confusing KeyError: No variable named '_subgrid_edge_indices'... if connectivity isn't populated #1888

Version

v2026.10.1

How did you install UXarray?

Source

What happened?

Calling UxDataArray.subset.bounding_box(...) on edge-centered data crashes with a very confusing error (see title), if face_edge_connectivity has not yet been populated.

Similar to #1758 but scoped to subsetting operations instead of isel and sel operations. Initially mentioned by @cmdupuis3 in #1875 (review).

Possibly also relevant: #1882.

I didn't test the other subset operations yet but since they also use _slice_from_grid I would expect similar behavior. While the title and description above are scoped only to bounding_box, the scope of this issue should actually be considered to be all subset operations; a full fix here should fix it for the other subset operations like bounding_circle and constant_latitude, too.

What did you expect to happen?

I expected a clearer error message, or for face_edge_connectivity to be populated automatically so that this operation can complete successfully.

Can you provide a MCVE to repoduce the bug?

import uxarray as ux
arr = ux.tutorial.open_dataset('quad-hexagon-random-edge')['random_data_edge']
arr.subset.bounding_box((-50, 50), (-50, 50))  # crashes

# but, if running the following before calling bounding_box():
arr.uxgrid.face_edge_connectivity

# then the bounding_box() command does not crash:
arr.subset.bounding_box((-50, 50), (-50, 50))