sync_turn called manager._flush_session() directly, which flushes
synchronously every turn no matter what writeFrequency says — the
"async", "session", and every-N-turns modes were dead configuration
on the main turn path. Route through save(), the dispatcher that
actually implements those modes.
Same bug class reported in #19650 (starship-s) and #72708 (Diaspar4u);
this takes the minimal one-line routing fix without their broader
lifecycle refactors.
Co-authored-by: starship-s <45587122+starship-s@users.noreply.github.com>
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