Combiner.__init__ builds a nested Array via xp.asarray([ccd.data ...]); array-api-strict requires xp.stack (44 failures)

[mwcraig]

Under CCDPROC_ARRAY_LIBRARY=array-api-strict (triage tooling from #937/#939, branch array-api-strict-triage-tooling), 44 of the 63 failures in ccdproc/tests/test_combiner.py (63 failed, 11 passed total) trace to a single line in Combiner.__init__. This is the biggest single failure source in the #941 escape-site table.

Offending code — ccdproc/combiner.py:189:

# set up the data array
self._data_arr = xp.asarray([ccd.data for ccd in ccd_list], dtype=dtype)

Root cause: each ccd.data is already an array_api_strict.Array. Passing a Python list of Array objects to xp.asarray triggers array-api-strict's explicit guard against nested arrays — it refuses to infer a stacking axis and requires xp.stack instead.

Representative traceback:

ccdproc/tests/test_combiner.py:87: in test_combiner_create
    c = Combiner(ccd_list)
ccdproc/combiner.py:189: in __init__
    self._data_arr = xp.asarray([ccd.data for ccd in ccd_list], dtype=dtype)
array_api_strict/_creation_functions.py:101: in asarray
    raise TypeError("Nested Arrays are not allowed. Use `stack` instead.")
E   TypeError: Nested Arrays are not allowed. Use `stack` instead.

Suggested fix: replace the list-comprehension + asarray with xp.stack([ccd.data for ccd in ccd_list], axis=0) (casting dtype separately via xp.astype if needed). The mask construction at combiner.py:196 (self._data_arr_mask = xp.asarray(mask_list, dtype=bool)) has the identical pattern and will hit the same error once the data-array construction is fixed, so it should be converted at the same time.

This is likely also the biggest CuPy failure source, since CuPy hits the same nested-array conversion path.

Part of the array-API triage in #941; found with the array-api-strict tooling from #937/#939. Verified at branch tip d329ac5 (2026-08-01): failure count and line number confirmed by re-running the suite and grepping tracebacks.

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