AppendString (CultNetSelectionEvaluator.cs) wrote value.Length, .NET's UTF-16
code-unit count, but Cursor.Parse's ReadLengthPrefixedFields slices that many
bytes out of the UTF-8-encoded body. An astral character (a surrogate pair:
2 UTF-16 units, 4 UTF-8 bytes) made the two counts disagree, so a cursor
minted for a row keyed with one (Evaluator_CursorPositionUsesCodePointOrderMatchingTheRowTiebreak's
astral key) failed to parse back - caught by that existing test on Yggdrasil,
not a new one. The prefix is now Encoding.UTF8.GetByteCount(value); the
digest's canonical string never round-trips through the byte-sliced reader
(it is hashed whole), so this only had to be right for the cursor body, but
one counting rule for both is what keeps AppendString actually unambiguous.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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