Kernel rig: export and print face cases in the import area

- file.export_step, export_stl, export_3mf, export_obj: a 30x20x10 box
  written and read back (the meshes converted to a solid): V 6000,
  A 2200, 6 faces, box (5,-10,0)-(35,10,10).
- file.export_urdf: a hinged arm on a grounded base: 3 links, 2 joints,
  and the base's mesh, written in metres, reads back as the
  1 x 0.5 x 0.2 box (V 0.1, A 1.6).
- body.print_face: a cylinder's flat end is accepted, its side refused.

PATHS adds the URDF writer and the print face modules.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DtL5M41G8Nua7HvuFPZkmJ

tests/kernel-cases/import/PATHS

@@ -1,14 +1,18 @@
 # The source files whose change reruns this area of the kernel rig (scripts/ci/kernel_rig_plan.py),
 # besides the shared core in ../PATHS-ALL. One git pathspec glob a line, relative to the
 # repository root; `#` starts a comment.
-# STEP and IGES import and export, mesh import (3MF, STL, OBJ, glTF) and mesh-to-solid conversion.
+# STEP and IGES import and export, mesh import and export (3MF, STL, OBJ, glTF, URDF), mesh-to-solid conversion
+# and the print face a body is laid on.
+crates/doc/src/print_face.rs
 crates/engine/src/cmd/file.rs
 crates/engine/src/cmd/file_import.rs
 crates/engine/src/cmd/mesh.rs
+crates/engine/src/cmd/print_face.rs
 crates/io/src/formats.rs
 crates/io/src/gltf_in.rs
 crates/io/src/obj.rs
 crates/io/src/threemf.rs
+crates/io/src/urdf.rs
 crates/kernel/src/iges_in.rs
 crates/kernel/src/iges_in/**
 crates/kernel/src/iges_out.rs

tests/kernel-cases/import/cov-export-3mf-box-round-trip/expected.json

@@ -0,0 +1,22 @@
+{
+ "sources": [],
+ "what": "a box written by Export 3MF, read back as a mesh and converted to a solid",
+ "source": "analytic",
+ "method": "box 30x20x10 from (5,-10,0): every face is flat, so its mesh is exact and the converted solid is the box: V = 6000, A = 2200, 6 faces, box (5,-10,0)-(35,10,10)",
+ "body_count": 1,
+ "faces": 6,
+ "volume_mm3": 6000.0,
+ "area_mm2": 2200.0,
+ "bbox": {
+  "min": [
+   5.0,
+   -10.0,
+   0.0
+  ],
+  "max": [
+   35.0,
+   10.0,
+   10.0
+  ]
+ }
+}

tests/kernel-cases/import/cov-export-3mf-box-round-trip/recipe.json

@@ -0,0 +1,49 @@
+{
+ "commands": [
+  {
+   "command": "solid.box",
+   "params": {
+    "length": 30,
+    "width": 20,
+    "height": 10,
+    "corner": [
+     5,
+     -10,
+     0
+    ],
+    "operation": "new",
+    "body_name": "Block"
+   }
+  },
+  {
+   "command": "file.export_3mf",
+   "params": {
+    "path": "$OUT/cov-export-3mf-box.3mf"
+   }
+  },
+  {
+   "command": "file.new",
+   "params": {
+    "name": "Reimported"
+   }
+  },
+  {
+   "command": "file.insert_mesh",
+   "params": {
+    "path": "$OUT/cov-export-3mf-box.3mf"
+   }
+  },
+  {
+   "command": "component.activate",
+   "params": {
+    "component": "cov-export-3mf-box"
+   }
+  },
+  {
+   "command": "mesh.convert",
+   "params": {
+    "body": "Block"
+   }
+  }
+ ]
+}

tests/kernel-cases/import/cov-export-obj-box-round-trip/expected.json

@@ -0,0 +1,22 @@
+{
+ "sources": [],
+ "what": "a box written by Export OBJ, read back as a mesh and converted to a solid",
+ "source": "analytic",
+ "method": "box 30x20x10 from (5,-10,0): every face is flat, so its mesh is exact and the converted solid is the box: V = 6000, A = 2200, 6 faces, box (5,-10,0)-(35,10,10)",
+ "body_count": 1,
+ "faces": 6,
+ "volume_mm3": 6000.0,
+ "area_mm2": 2200.0,
+ "bbox": {
+  "min": [
+   5.0,
+   -10.0,
+   0.0
+  ],
+  "max": [
+   35.0,
+   10.0,
+   10.0
+  ]
+ }
+}

tests/kernel-cases/import/cov-export-obj-box-round-trip/recipe.json

@@ -0,0 +1,49 @@
+{
+ "commands": [
+  {
+   "command": "solid.box",
+   "params": {
+    "length": 30,
+    "width": 20,
+    "height": 10,
+    "corner": [
+     5,
+     -10,
+     0
+    ],
+    "operation": "new",
+    "body_name": "Block"
+   }
+  },
+  {
+   "command": "file.export_obj",
+   "params": {
+    "path": "$OUT/cov-export-obj-box.obj"
+   }
+  },
+  {
+   "command": "file.new",
+   "params": {
+    "name": "Reimported"
+   }
+  },
+  {
+   "command": "file.insert_mesh",
+   "params": {
+    "path": "$OUT/cov-export-obj-box.obj"
+   }
+  },
+  {
+   "command": "component.activate",
+   "params": {
+    "component": "cov-export-obj-box"
+   }
+  },
+  {
+   "command": "mesh.convert",
+   "params": {
+    "body": "Block"
+   }
+  }
+ ]
+}

tests/kernel-cases/import/cov-export-step-box-round-trip/expected.json

@@ -0,0 +1,22 @@
+{
+ "sources": [],
+ "what": "a box written by Export STEP and read back",
+ "source": "analytic",
+ "method": "box 30x20x10 from (5,-10,0): V = 6000, A = 2(600 + 300 + 200) = 2200, 6 faces, box (5,-10,0)-(35,10,10). The re-imported body is graded, not the exported one (the design holds only the import)",
+ "body_count": 1,
+ "faces": 6,
+ "volume_mm3": 6000.0,
+ "area_mm2": 2200.0,
+ "bbox": {
+  "min": [
+   5.0,
+   -10.0,
+   0.0
+  ],
+  "max": [
+   35.0,
+   10.0,
+   10.0
+  ]
+ }
+}

tests/kernel-cases/import/cov-export-step-box-round-trip/recipe.json

@@ -0,0 +1,37 @@
+{
+ "commands": [
+  {
+   "command": "solid.box",
+   "params": {
+    "length": 30,
+    "width": 20,
+    "height": 10,
+    "corner": [
+     5,
+     -10,
+     0
+    ],
+    "operation": "new",
+    "body_name": "Block"
+   }
+  },
+  {
+   "command": "file.export_step",
+   "params": {
+    "path": "$OUT/cov-export-step-box.step"
+   }
+  },
+  {
+   "command": "file.new",
+   "params": {
+    "name": "Reimported"
+   }
+  },
+  {
+   "command": "file.insert_step",
+   "params": {
+    "path": "$OUT/cov-export-step-box.step"
+   }
+  }
+ ]
+}

tests/kernel-cases/import/cov-export-stl-box-round-trip/expected.json

@@ -0,0 +1,22 @@
+{
+ "sources": [],
+ "what": "a box written by Export STL, read back as a mesh and converted to a solid",
+ "source": "analytic",
+ "method": "box 30x20x10 from (5,-10,0): every face is flat, so its mesh is exact and the converted solid is the box: V = 6000, A = 2200, 6 faces, box (5,-10,0)-(35,10,10)",
+ "body_count": 1,
+ "faces": 6,
+ "volume_mm3": 6000.0,
+ "area_mm2": 2200.0,
+ "bbox": {
+  "min": [
+   5.0,
+   -10.0,
+   0.0
+  ],
+  "max": [
+   35.0,
+   10.0,
+   10.0
+  ]
+ }
+}

tests/kernel-cases/import/cov-export-stl-box-round-trip/recipe.json

@@ -0,0 +1,49 @@
+{
+ "commands": [
+  {
+   "command": "solid.box",
+   "params": {
+    "length": 30,
+    "width": 20,
+    "height": 10,
+    "corner": [
+     5,
+     -10,
+     0
+    ],
+    "operation": "new",
+    "body_name": "Block"
+   }
+  },
+  {
+   "command": "file.export_stl",
+   "params": {
+    "path": "$OUT/cov-export-stl-box.stl"
+   }
+  },
+  {
+   "command": "file.new",
+   "params": {
+    "name": "Reimported"
+   }
+  },
+  {
+   "command": "file.insert_mesh",
+   "params": {
+    "path": "$OUT/cov-export-stl-box.stl"
+   }
+  },
+  {
+   "command": "component.activate",
+   "params": {
+    "component": "cov-export-stl-box"
+   }
+  },
+  {
+   "command": "mesh.convert",
+   "params": {
+    "body": "cov-export-stl-box"
+   }
+  }
+ ]
+}

tests/kernel-cases/import/cov-export-urdf-arm-on-a-base/expected.json

@@ -0,0 +1,20 @@
+{
+ "sources": [],
+ "what": "an arm hinged on a grounded base written by Export URDF, and the base's mesh read back",
+ "source": "analytic",
+ "method": "Base (grounded): box 1000x500x200; Arm: box 400x100x100 on a revolute joint. The tree: base_link, Base fixed to it, Arm on the revolute: 3 links, 2 joints. Meshes are written in metres, so the base's STL read back as millimetres is the box 1 x 0.5 x 0.2: V = 0.1, A = 2(0.5 + 0.2 + 0.1) = 1.6, 6 faces",
+ "body_count": 1,
+ "faces": 6,
+ "volume_mm3": 0.1,
+ "area_mm2": 1.6,
+ "results": [
+  {
+   "step": 8,
+   "json": {
+    "format": "Urdf",
+    "links": 3,
+    "joints": 2
+   }
+  }
+ ]
+}

tests/kernel-cases/import/cov-export-urdf-arm-on-a-base/recipe.json

@@ -0,0 +1,135 @@
+{
+ "commands": [
+  {
+   "command": "solid.box",
+   "params": {
+    "length": 1000,
+    "width": 500,
+    "height": 200,
+    "corner": [
+     -500,
+     -250,
+     -200
+    ],
+    "operation": "new",
+    "body_name": "BaseBox"
+   }
+  },
+  {
+   "command": "solid.box",
+   "params": {
+    "length": 400,
+    "width": 100,
+    "height": 100,
+    "corner": [
+     0,
+     -50,
+     0
+    ],
+    "operation": "new",
+    "body_name": "ArmBox"
+   }
+  },
+  {
+   "command": "component.create",
+   "params": {
+    "name": "Base",
+    "parent": "root",
+    "activate": false,
+    "grounded": true
+   }
+  },
+  {
+   "command": "component.move_bodies",
+   "params": {
+    "bodies": [
+     "BaseBox"
+    ],
+    "component": "Base"
+   }
+  },
+  {
+   "command": "component.create",
+   "params": {
+    "name": "Arm",
+    "parent": "root",
+    "activate": false,
+    "grounded": false
+   }
+  },
+  {
+   "command": "component.move_bodies",
+   "params": {
+    "bodies": [
+     "ArmBox"
+    ],
+    "component": "Arm"
+   }
+  },
+  {
+   "command": "joint.create",
+   "params": {
+    "type": "revolute",
+    "name": "Hinge",
+    "flip": true,
+    "a": {
+     "occurrence": "Base",
+     "point": [
+      0,
+      0,
+      0
+     ],
+     "z": [
+      0,
+      0,
+      1
+     ]
+    },
+    "b": {
+     "occurrence": "Arm",
+     "point": [
+      0,
+      0,
+      0
+     ],
+     "z": [
+      0,
+      0,
+      1
+     ]
+    },
+    "quiet": true
+   }
+  },
+  {
+   "command": "file.export_urdf",
+   "params": {
+    "path": "$OUT/cov-export-urdf-arm.urdf"
+   }
+  },
+  {
+   "command": "file.new",
+   "params": {
+    "name": "Reimported"
+   }
+  },
+  {
+   "command": "file.insert_mesh",
+   "params": {
+    "path": "$OUT/cov-export-urdf-arm-Base.stl"
+   }
+  },
+  {
+   "command": "component.activate",
+   "params": {
+    "component": "cov-export-urdf-arm-Base"
+   }
+  },
+  {
+   "command": "mesh.convert",
+   "params": {
+    "body": "cov-export-urdf-arm-Base"
+   }
+  }
+ ]
+}

tests/kernel-cases/import/cov-print-face-on-a-flat-end/expected.json

@@ -0,0 +1,17 @@
+{
+ "sources": [],
+ "what": "a cylinder's flat end marked as the face a slicer export lays it on",
+ "source": "analytic",
+ "method": "(3,4,20) is on the top end of the cylinder r 10, h 20 about z: a flat face, so it is marked, and the body is unchanged: V = pi*100*20 = 6283.1853, 3 faces",
+ "body_count": 1,
+ "faces": 3,
+ "volume_mm3": 6283.185307,
+ "results": [
+  {
+   "step": 2,
+   "json": {
+    "body": "Peg"
+   }
+  }
+ ]
+}

tests/kernel-cases/import/cov-print-face-on-a-flat-end/recipe.json

@@ -0,0 +1,23 @@
+{
+ "commands": [
+  {
+   "command": "solid.cylinder",
+   "params": {
+    "radius": 10,
+    "height": 20,
+    "body_name": "Peg"
+   }
+  },
+  {
+   "command": "body.print_face",
+   "params": {
+    "body": "Peg",
+    "point": [
+     3,
+     4,
+     20
+    ]
+   }
+  }
+ ]
+}

tests/kernel-cases/import/cov-print-face-refuses-a-curved-face/expected.json

@@ -0,0 +1,8 @@
+{
+ "sources": [],
+ "what": "a cylinder's side picked as the face a slicer export lays it on",
+ "source": "analytic",
+ "method": "(10,0,10) is on the side of the cylinder r 10, h 20 about z: a curved face, which no body can lie flat on: refused",
+ "outcome": "refused",
+ "refusal": "only a flat face can be the print face"
+}

tests/kernel-cases/import/cov-print-face-refuses-a-curved-face/recipe.json

@@ -0,0 +1,23 @@
+{
+ "commands": [
+  {
+   "command": "solid.cylinder",
+   "params": {
+    "radius": 10,
+    "height": 20,
+    "body_name": "Peg"
+   }
+  },
+  {
+   "command": "body.print_face",
+   "params": {
+    "body": "Peg",
+    "point": [
+     10,
+     0,
+     10
+    ]
+   }
+  }
+ ]
+}