Survey Grid v1 at equator bug

hi,
When setting a grid survey on each side of the equator (so latitude is positive and negative) I get coords like -7903575728.1829500 557114566423.8260000 -> upper edge of the world

Reproduce the Survey Grid v1 case with survey points on both positive and negative sides of the equator, using the coordinates and screenshot in the report as the starting reference. Trace the survey-grid coordinate handling and verify that the generated coordinates remain valid rather than jumping to the upper edge of the world; add or run a regression check for this scenario.

Written by the indexing model from the issue text.