The coordinates that carry a sub-field prompt. v1's rule, preserved verbatim: a coordinate
whose value is non-blank is a sub-field prompt box; a NULL value is the annotation's own
bounding box. Spatial columns are nullable TEXT and are irrelevant here, so nulls elsewhere on
the coordinate never affect the partition.
The coordinates that carry a sub-field prompt. v1's rule, preserved verbatim: a coordinate whose
valueis non-blank is a sub-field prompt box; a NULLvalueis the annotation's own bounding box. Spatial columns are nullable TEXT and are irrelevant here, so nulls elsewhere on the coordinate never affect the partition.