notes update. add another poly.union update in fmd slice

notes.md

@@ -60,6 +60,7 @@
 * `B` outside cutting direction in roughing mode inverted
 * `B` clear voids has double interior pass because wrong offset shadow used
 * `B` top clearing operations should use linear, not offset, passes
+* `F` use 3 registration holes to prevent rotation accidents (midline offset one axis)
 * `F` parameterize dropping close points in prep.js. ensure long segments remain straight
 * `F` flat and volumetric rendering of paths
 * `F` z bounded slices (extension of z bottom offset feature)

src/mode/fdm/slice.js

@@ -918,7 +918,7 @@
 
         // return top.supports = supports;
         // then union supports
-        supports = POLY.union(supports);
+        supports = POLY.union(supports, null, true);
 
         // constrain support poly to top polys
         supports = POLY.trimTo(supports, trimTo);