nx_anchor_feature.nx

nx_anchor_feature.nx -- singular landmark-feature contributions. Solves the "generic FBM noise" problem for procgen worlds. Pure fractional Brownian motion gives terrain that LOOKS LIKE A WORLD in the abstract but has no signature features. Real worlds have landmarks that POP: Olympus Mons (22 km shield volcano, single massive cone), Hellas Basin (7 km deep impact crater 2300 km across), Valles Marineris (4000 km canyon system), Mt Everest, Mariana Trench, Caloris Basin on Mercury. This primitive ships the SHAPE FUNCTIONS for those features. Caller queries a feature's contribution at a (px, py) world coord; composer adds the contribution to the base FBM height. Body- specific anchor lists (Olympus Mons at 18 N 226 E, etc.) ship in nishi-engine/nx as the per-body data layer that composes this primitive into the surface generator. V1 kinds shipped (3): VOLCANIC_DOME -- Olympus Mons style: single radial peak with parabolic falloff (smooth shield-volcano profile) IMPACT_BASIN -- Hellas style: large circular depression with optional raised rim (negative magnitude) RIDGE -- mountain-range linear feature, 4-cardinal orientations (N-S or E-W in v1; arbitrary angle in v2 via nx_camera_q14 sin/cos import) V2 kinds queued (2): CANYON -- Valles Marineris style: linear depression with optional inner ridge / chasma structure PLATEAU -- Tharsis Bulge style: smooth flat-topped uplift Per cardinal `feedback-procgen-causal-growth-not-direct-sampling`: anchor features ARE the causal layer that makes one world feel distinct from another. Without them you get noise; with them you get geography. Loss audit: Q14 integer arithmetic throughout. Parabolic falloff is exact in Q14. Linear-feature distance is exact for the 2 cardinal orientations supported in v1.