fix(mpack): boundary values for negative integer encoding
Problem:
libmpack encodes boundary values -129 and -32769 with wrong integer
sizes:
- -129 as int8 instead of int16
- -32769 as int16 instead of int32
because the boundary checks compare against the wrong values (e.g., lo
< 0xffffff7f instead of lo < 0xffffff80). This caused data corruption:
-129 would decode as 127.
Solution:
Fix off-by-one errors in the two's complement boundary constants:
0xffffff80 (-128, min int8) and 0xffff8000 (-32768, min int16).
Co-authored-by: benarcher2691 <ben.archer2691@gmail.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
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