D031 string_slice_not_char_boundary
String.slice was given a byte offset that is not on a UTF-8 character boundary.
A runtime defect: the running program stops with it; no compile phase reports it, and try cannot catch it. sakura explain D031 prints this explanation offline.
String.slice was given a byte offset that is not on a UTF-8 character boundary. Offsets are
bytes, not characters: derive them from the string itself rather than from a character count.
Runtime defects come from running programs, so compiler/tests/ui has no fixture for them; the explanation above names the repair.