nx_geo_hull.nx

nx_geo_hull.nx -- LIB: GEO-012 CONVEX HULL (Andrew's monotone chain), INTEGER-EXACT. THE EXCEED ANGLE (measured, not asserted): the turn-direction test is a single INTEGER cross product over microdegree coordinates -- ZERO floating point. So the orientation predicate is EXACT, and collinear / duplicate points are classified deterministically (cross == 0 is decided, never a float epsilon coin-flip). Those are exactly the inputs where Turf.js / Shapely / qhull (float) emit non-deterministic hulls or spurious near-collinear vertices. We drop collinear edge points (pop on cross <= 0) for a minimal, exact hull. Convention (matches nx_geo): pts = flat [lat0,lon0, ...], n points, lat = Y, lon = X. Writes the hull vertex INDICES (into pts) in counter-clockwise order to out_idx; returns the hull size. Overflow-safe for Earth coords in i64 (cross of two deltas <= 3.6e8^2 ~ 1.3e17, no accumulation). Selection-sort O(n^2) for now (exactness first; an O(n log n) sort is a later perf rung). license_tier: ORIGINAL