Kernel rig: #316's bottom rounds as large as the wall, or larger, shell with a step wall at the opening, not refused

Where the round meets the open bottom the cavity's wall steps down along the bottom's normal, so the
round meets it at 90 degrees and the opening is exactly the picked face. The cases are renamed and
graded on the exact volumes, and come off the shell known-failing list.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/kernel-cases/shell/316-shell-open-beside-a-bottom-round-r2-4-as-large-as-the-wall-refused/expected.json

@@ -1,10 +0,0 @@
-{
- "sources": [
-  "tangency-labs/solidcraft#316"
- ],
- "what": "a 40 x 30 x 10 box, its bottom outline rounded R2.4, shelled 2 mm open at the bottom: the cavity's walls stand 2 in, where the round meets the bottom, so the rim would have no thickness: refused, naming the rim",
- "source": "analytic",
- "method": "the open bottom's rim runs from the round's contact with the bottom (r = 2.4 in from the outside) to the cavity's wall (2 in): the round's contact lies past the wall, so there is no rim; refused",
- "outcome": "refused",
- "refusal": "not supported yet: the rim"
-}

tests/kernel-cases/shell/316-shell-open-beside-a-bottom-round-r2-4-larger-than-the-wall-steps/expected.json

@@ -0,0 +1,22 @@
+{
+ "sources": [
+  "tangency-labs/solidcraft#316"
+ ],
+ "what": "a 40 x 30 x 10 box, its bottom outline rounded R2.4, shelled 2 mm open at the bottom: where the round meets the open bottom the cavity's wall steps down along the bottom's normal (a step wall), so the round meets it at 90 degrees at the opening's edge and the opening is exactly the picked face",
+ "source": "analytic",
+ "method": "box 40x30x10 less the bottom rounds R2.4 (the four edges mitred at the vertical corners), less the cavity: the walls and top moved 2 in, the open bottom kept, and at the bottom's tangent edge with the round a step wall along the bottom's normal from the bottom (offset 0) to the round's offset (offset 2); the round's offset has radius 0.4. The material along each bottom edge is a mitred ring of section t(r - t) + (1 - pi/4)(r - t)^2 on top of the walls' plain sections; integrated round the outline with the mitred corners (quadrature agrees to 3e-5): V = 4446.399483",
+ "body_count": 1,
+ "volume_mm3": 4446.399483,
+ "bbox": {
+  "min": [
+   0,
+   0,
+   0
+  ],
+  "max": [
+   40,
+   30,
+   10
+  ]
+ }
+}

tests/kernel-cases/shell/316-shell-open-beside-a-bottom-round-r2-as-large-as-the-wall-refused/expected.json

@@ -1,10 +0,0 @@
-{
- "sources": [
-  "tangency-labs/solidcraft#316"
- ],
- "what": "a 40 x 30 x 10 box, its bottom outline rounded R2, shelled 2 mm open at the bottom: the cavity's walls stand 2 in, where the round meets the bottom, so the rim would have no thickness: refused, naming the rim",
- "source": "analytic",
- "method": "the open bottom's rim runs from the round's contact with the bottom (r = 2 in from the outside) to the cavity's wall (2 in): 0 wide, so there is no rim; refused",
- "outcome": "refused",
- "refusal": "not supported yet: the rim"
-}

tests/kernel-cases/shell/316-shell-open-beside-a-bottom-round-r2-as-large-as-the-wall-steps/expected.json

@@ -0,0 +1,22 @@
+{
+ "sources": [
+  "tangency-labs/solidcraft#316"
+ ],
+ "what": "a 40 x 30 x 10 box, its bottom outline rounded R2, shelled 2 mm open at the bottom: where the round meets the open bottom the cavity's wall steps down along the bottom's normal (a step wall), so the round meets it at 90 degrees at the opening's edge and the opening is exactly the picked face",
+ "source": "analytic",
+ "method": "box 40x30x10 less the bottom rounds R2 (the four edges mitred at the vertical corners), less the cavity: the walls and top moved 2 in, the open bottom kept, and at the bottom's tangent edge with the round a step wall along the bottom's normal from the bottom (offset 0) to the round's offset (offset 2); the round's offset has radius 0. The material along each bottom edge is a mitred ring of section t(r - t) + (1 - pi/4)(r - t)^2 on top of the walls' plain sections; integrated round the outline with the mitred corners (quadrature agrees to 3e-5): V = 4394.890822",
+ "body_count": 1,
+ "volume_mm3": 4394.890822,
+ "bbox": {
+  "min": [
+   0,
+   0,
+   0
+  ],
+  "max": [
+   40,
+   30,
+   10
+  ]
+ }
+}

tests/kernel-cases/shell/KNOWN_FAILING

@@ -2,6 +2,4 @@
 # rig gate (.github/workflows/kernel-rig.yml) fails on a case that fails and is not listed here,
 # and on a listed case that passes: a fix removes its line in the same pull request.
 # Baseline: 45f69c0e5 with SMLib 60b1c6a, aarch64 Linux.
-316-shell-open-beside-a-bottom-round-r2-4-as-large-as-the-wall-refused builds a shell where the rim has no thickness instead of refusing it
-316-shell-open-beside-a-bottom-round-r2-as-large-as-the-wall-refused builds a shell where the rim has no thickness instead of refusing it
 cov-shell-again-open-at-an-inner-wall-of-a-shelled-box SMLib status 1001