Blends: a curved seam where the edge chain runs on holds the contact on itself (#1291)

A round or chamfer whose edge chain runs on across a curved seam (the end circle of a lofted tube whose axis bends) is now built: the section solve keeps its contact on the seam through a plane taken afresh at the seam's nearest point at each step. Straight seams are unchanged. Robustness seed 41 is re-recorded: its second fillet, refused before, now builds. Fixes #1213.

Co-authored-by: gvocale <[email protected]>

crates/engine/src/tests.rs

@@ -306,6 +306,7 @@ fn join_of_a_lobed_disc_pattern_is_not_refused() {
 mod blend_fit;
 mod boolean_diagnostics;
 mod component_frames;
+mod curved_seam_round;
 mod large_step_import;
 mod loft_cut;
 mod loft_ring;