Card 59 started — the "how long until price comes back?" ruler, answer key frozen S1 DONE

Feature 2 of 4 began: card 59, the "forward visibility horizon". For every bar it asks a beautifully simple question: from this bar's closing price, how many bars into the future until the price closes at that level or higher again? If the answer over the last 200 bars averages ~2, dips are being bought back almost immediately; if it averages ~15, levels take a long time to be reclaimed. On the frozen reference data the average sits around 6 bars — with excursions from ~2.2 (relentless buying) to ~17.8 (long underwater stretches). Bars whose level is never re-reached before the window ends are honestly dropped, not guessed.

Why "visibility"? The name comes from a physics technique that turns a price series into a network of bars that can "see" each other over intervening bars. This feature's number is exactly a node's forward sight distance in that construction — but the arithmetic needs no network at all: it's a plain "first time the level is re-touched" scan. Simpler arithmetic = fewer places for bugs to hide.

The answer key was double-checked by two very different algorithms: the straightforward scan (look forward bar by bar), and a cleverer one-pass method using a "monotonic stack" — a completely different route to the same integers. Both had to agree exactly — not approximately — on all 19,602 windows, plus known-answer drills (an always-rising market must score exactly 1.0; an always-falling one must honestly say "undefined"; a tiny hand-worked example must give exactly 5/3). All passed.

Good news for effort: unlike feature 1 (which needed a brand-new dataset carrying bar durations), this one reads only closing prices — so it reuses the exact fingerprint-locked datasets every earlier feature trusts. And because the computation is just comparisons plus one division, the upcoming Rust version is expected to match the reference to the last binary digit — zero tolerance headroom needed.