Morning improvements

server-rs/src/utils/grid_index.rs

@@ -138,6 +138,26 @@ impl GridIndex {
         result
     }
 
+    /// Count the number of row indices within the given bounds without allocating.
+    /// O(grid cells in bounds) — much cheaper than query() for threshold decisions.
+    pub fn count_in_bounds(&self, south: f64, west: f64, north: f64, east: f64) -> usize {
+        let Some((row_min, row_max, col_min, col_max)) =
+            self.clamp_bounds(south, west, north, east)
+        else {
+            return 0;
+        };
+
+        let mut count = 0usize;
+        for row in row_min..=row_max {
+            let row_start = row * self.cols;
+            for col in col_min..=col_max {
+                let cell_idx = row_start + col;
+                count += (self.offsets[cell_idx + 1] - self.offsets[cell_idx]) as usize;
+            }
+        }
+        count
+    }
+
     #[inline]
     pub fn for_each_in_bounds(
         &self,
@@ -334,4 +354,27 @@ mod tests {
         let result = grid.query(-90.0, -180.0, 90.0, 180.0);
         assert_eq!(result.len(), 2);
     }
+
+    #[test]
+    fn count_in_bounds_matches_query_len() {
+        let lat = vec![51.5_f32, 51.6, 51.7, 52.0];
+        let lon = vec![-0.1_f32, -0.1, -0.1, -0.1];
+        let grid = GridIndex::build(&lat, &lon, 0.01);
+
+        let bounds = (51.4, -0.2, 51.8, 0.0);
+        assert_eq!(
+            grid.count_in_bounds(bounds.0, bounds.1, bounds.2, bounds.3),
+            grid.query(bounds.0, bounds.1, bounds.2, bounds.3).len()
+        );
+
+        // Full bounds
+        let full = (50.0, -1.0, 53.0, 1.0);
+        assert_eq!(
+            grid.count_in_bounds(full.0, full.1, full.2, full.3),
+            grid.query(full.0, full.1, full.2, full.3).len()
+        );
+
+        // Empty bounds
+        assert_eq!(grid.count_in_bounds(0.0, 0.0, 1.0, 1.0), 0);
+    }
 }