{%- if loop.first %}
{{- "[Round " ~ (ns.rounds) ~ "] USER:" }}
{%- else %}
{{- " [Round " ~ (ns.rounds) ~ "] USER:"}}
It appears there's no way to use LongCat-Flash-Chat with most frontends except with chat completion mode.
SillyTavern's aggressively useless STScript allegedly can increment variables but even macros don't work right/consistently in instruction templates so I'm not even going to try it.