putUInt64String used cvtUlongToString, which is cvtUInt32ToString, so the 64-bit source was narrowed to its low 32 bits (e.g. 0x1_0000_0007 printed as "7"). Use cvtUInt64ToString, matching getUInt64String and every other width-specific putXxxString. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>