Engine: the meshing commands pass the design's edge seeds to the meshers

mesh.tet.generate, mesh.hex.*, mesh.hex.blocks and mesh.cells give every
seed on the open design to their meshers, which match them to their own
curves by position, so a seed on an edge two cells share holds in both. The
tet reply gives, per seed, the mesh edges along it. Docs and the roadmap
say what is honoured where.

Fixes #230.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/geometry/src/edges.rs

@@ -15,7 +15,7 @@ use crate::{Result, Shape, SurfaceMesh};
 
 /// Tessellation tolerance (a fraction of the body's size) of [`Shape::edges`]: the edge polylines
 /// are for display, picking and matching edges by position.
-const EDGE_TOLERANCE: f64 = 1e-3;
+pub const EDGE_TOLERANCE: f64 = 1e-3;
 
 /// A B-rep edge of a body.
 #[derive(Debug, Clone, PartialEq)]

crates/geometry/src/lib.rs

@@ -25,7 +25,7 @@ pub mod sample;
 mod script;
 
 pub use design::{Design, FeatureError, MAX_DESIGN_BYTES, open_design};
-pub use edges::Edge;
+pub use edges::{EDGE_TOLERANCE, Edge};
 pub use partition::{Cut, CutReport};
 pub mod tagged_mesh;
 #[cfg(feature = "scripts")]