Boundary semantics

LocateTile uses unambiguous, verifier-friendly boundary rules.

• Longitude is half-open: [-180°, +180°)
• Latitude includes poles: [-90°, +90°]
• Tile assignment uses floor semantics
• Points exactly on a tile edge map to the tile with the lower index
• The North Pole maps deterministically to the topmost row (iy = NY - 1)

These rules prevent ambiguity and cross-implementation disagreement.