A calendar/flow-event strategy on a data estate the factory has NEVER touched: Hong Kong equities (HKEQ, 174 liquid names, clean split-adjusted daily bars 2018-01-02 -> 2026-08, venue already wired in venue_configs.py as a CASH account at 0.11% per side). Mechanism: a large and mechanically-mandated share of daily turnover in HK large caps is mainland money arriving through Shanghai/Shenzhen-Hong Kong Stock Connect (southbound). When mainland exchanges close for a multi-day public holiday (Lunar New Year, Qingming, Labour Day, Dragon Boat, Mid-Autumn, National Day/Golden Week, New Year) Connect southbound trading is SUSPENDED while HKEX keeps trading. For those sessions a persistent, price-insensitive buy-side flow is removed from the HK book by regulation, not by sentiment; high-southbound-ownership H-shares trade thinner and drift soft. When the mainland reopens, the suspended flow returns in a burst. The strategy is long the flow-return: buy an equal-weighted basket of 10 high-southbound HK large caps at the close of the LAST HK session inside the closure window and hold through the reopening. This is not a momentum, mean-reversion, pairs, ETF-rotation, funding or liquidation idea — no family in the 1330-hypothesis corpus resembles it, and no experiment has ever run on HKEQ (0 of 3068). The closure calendar is known history, so the whole 8.7 years is backtestable today with zero data-availability risk. The mainland-holiday state is derived ONLINE, not hardcoded: 000001.CNEQ is subscribed as a SIGNAL-ONLY heartbeat (never traded) — if no CNEQ daily bar has printed for >= mainland_closed_days calendar days while HK bars keep arriving, the mainland is closed. Permitted fallback if the extra CNEQ venue proves awkward in the engine: a static table of mainland holiday windows 2018-2027 (ex-ante known, no lookahead).