\setuphead [chapter][resetnumber=no]
\setupsection[section][previousnumber=no]
</texcode>
This is handled differently in mkiv (where "resetnumber=no" is silently ignored):
<texcode>
\definestructurereset[default][1,1,0][1] % reset part, chapter, but not section
\setuphead[sectionresetset=default]
</texcode>