Add ARB6 and ARB7 detection to csg-g polyhedron import

ARB6 (triangular prism): 6 vertices, 5 faces (2 triangles + 3 quads).
Identifies opposing triangle faces and pairs vertices via shared
side quads.

ARB7 (arb8 with one collapsed corner): 7 vertices, 6 faces
(2 triangles + 4 quads).  Finds the bottom quad, identifies top
vertices, and pairs via face adjacency.

Previously these fell through to BOT.

doc/asciidoc/system/man1/CMakeLists.txt

@@ -34,6 +34,7 @@ set(
   coil.adoc
   comgeom-g.adoc
   conv-vg2g.adoc
+  csg-g.adoc
   cv.adoc
   dbupgrade.adoc
   decimate.adoc
@@ -70,6 +71,7 @@ set(
   g-obj.adoc
   g-ply.adoc
   g-raw.adoc
+  g-scad.adoc
   g-shell-rect.adoc
   g-step.adoc
   g-stl.adoc

doc/asciidoc/system/man1/csg-g.adoc

@@ -0,0 +1,61 @@
+= CSG-G(1)
+:doctype: manpage
+:mansource: BRL-CAD
+:manmanual: User Commands
+
+== NAME
+csg-g - OpenSCAD CSG Translator (CSG to BRL-CAD)
+
+== SYNOPSIS
+
+[source]
+----
+csg-g [-d] file.csg file.g
+----
+
+
+[[description]]
+== DESCRIPTION
+
+*csg-g* converts an OpenSCAD evaluated CSG file (_file.csg_) to a BRL-CAD _file.g_ file. The CSG format is produced by running `openscad -o file.csg input.scad` and contains the fully evaluated CSG tree with all variables, modules, and loops resolved.
+
+The converter preserves CSG structure, mapping OpenSCAD primitives and boolean operations directly to BRL-CAD equivalents rather than tessellating to mesh. Supported primitives include cube (RPP), sphere (SPH), cylinder (TGC), polyhedron (ARB or BOT), torus via rotate_extrude of circle (TOR), and extrusions of square, circle, and polygon profiles (RPP, TGC, or sketch+extrusion). Boolean operations (difference, union, intersection, group) and transformation matrices (multmatrix) are preserved. Colors are stored as object attributes. The `import()` node reads and inlines referenced STL files as BOT primitives.
+
+Polyhedra are matched against ARB4, ARB5, and ARB8 when the vertex and face counts match and the shape is convex. Non-convex polyhedra and unmatched shapes fall back to BOT (bag of triangles).
+
+The *-d* option prints debugging information during conversion.
+
+
+[[example]]
+== EXAMPLE
+
+
+----
+
+$ openscad -o model.csg model.scad
+$ csg-g model.csg model.g
+----
+
+
+[[see_also]]
+== SEE ALSO
+
+*g-scad*(1), *stl-g*(1), *openscad*(1)
+
+
+[[author]]
+== AUTHOR
+
+BRL-CAD Team
+
+
+[[copyright]]
+== COPYRIGHT
+
+This software is Copyright (c) 2025 by the United States Government as represented by U.S. Army Research Laboratory.
+
+
+[[bug_reports]]
+== BUG REPORTS
+
+Reports of bugs or problems should be submitted via electronic mail to devs@brlcad.org

doc/asciidoc/system/man1/g-scad.adoc

@@ -0,0 +1,59 @@
+= G-SCAD(1)
+:doctype: manpage
+:mansource: BRL-CAD
+:manmanual: User Commands
+
+== NAME
+g-scad - BRL-CAD to OpenSCAD Translator (BRL-CAD to SCAD)
+
+== SYNOPSIS
+
+[source]
+----
+g-scad [-d] [-o output.scad] file.g object(s)
+----
+
+
+[[description]]
+== DESCRIPTION
+
+*g-scad* converts the specified BRL-CAD objects from _file.g_ to OpenSCAD format. The output preserves CSG structure, mapping BRL-CAD boolean operations and primitives directly to OpenSCAD equivalents rather than tessellating everything to polyhedron.
+
+Direct primitive mappings: SPH and ELL to sphere(), TGC and REC to cylinder(), ARB to polyhedron(), BOT to polyhedron(), TOR to rotate_extrude(circle()), PARTICLE to hull() of two spheres, PIPE to union of cylinders and spheres, EXTRUDE to linear_extrude(polygon()), REVOLVE to rotate_extrude(polygon()), and HALF to a large translated cube. Combination colors are emitted as color() wrappers. Primitives without direct mappings are tessellated via their ft_tessellate method and emitted as polyhedron().
+
+The *-d* option prints debugging information. The *-o* option specifies the output file (default is stdout).
+
+
+[[example]]
+== EXAMPLE
+
+
+----
+
+$ g-scad -o model.scad model.g all.g
+$ openscad model.scad
+----
+
+
+[[see_also]]
+== SEE ALSO
+
+*csg-g*(1), *g-stl*(1), *openscad*(1)
+
+
+[[author]]
+== AUTHOR
+
+BRL-CAD Team
+
+
+[[copyright]]
+== COPYRIGHT
+
+This software is Copyright (c) 2025 by the United States Government as represented by U.S. Army Research Laboratory.
+
+
+[[bug_reports]]
+== BUG REPORTS
+
+Reports of bugs or problems should be submitted via electronic mail to devs@brlcad.org

src/conv/CMakeLists.txt

@@ -31,6 +31,10 @@ brlcad_addexec(comgeom-g "${comgeom-g_SRCS}" "libwdb;libbn;libbu;${M_LIBRARY}" F
 
 brlcad_addexec(conv-vg2g conv-vg2g.c "libbu" FOLDER Conv)
 
+brlcad_addexec(csg-g csg/csg-g.c "libwdb;librt;libbu" FOLDER Conv)
+
+brlcad_addexec(g-scad csg/g-scad.c "libwdb;librt;libnmg;libbu" FOLDER Conv)
+
 brlcad_addexec(dbupgrade dbupgrade.c "libwdb;librt;libbu" FOLDER Conv)
 
 brlcad_addexec(dxf-g dxf/dxf-g.c "libwdb;librt;libnmg;libbn;libbu;${M_LIBRARY}" FOLDER Conv)