The topic was only being injected into the initial breakthrough message via
get_argument_start_prompt(). After that, every subsequent exchange called
get_miku_argument_prompt() / get_evil_argument_prompt() which had no concept
of the topic — so both personas forgot what they were arguing about after the
first exchange and reverted to generic identity-crisis arguments.
Fix: added argument_topic parameter to both persona prompt functions and inject
it as a bold ARGUMENT THEME reminder in every single exchange. The topic block
explicitly tells the LLM to stay on-topic and not drift into generic territory.