diag: VCOPY logging in value-copy hook + field-index finding

Root cause of no-match: GetBitRange's 3rd arg (captured as _currentFieldIndex) is
a field-PATH TOKEN (from the changed-field list param_8), NOT a direct index into
serializer+0x10. ResolveFieldName uses it as an array index -> out of range ->
name='' -> never matches m_iHealth. The positional index (iStack_18bb8) is
WFL-internal, not passed to GetBitRange. VCOPY#n logs ser/fieldIdx/name/bits/client
(first 50) to confirm live + reveal the token values.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>