Kernel rig: replace face cases, a top moved onto a plane and a lower step raised to the higher top (fails today: SMLib offset of faces refuses closing the step wall)

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

tests/kernel-cases/shell/KNOWN_FAILING

@@ -1,4 +1,5 @@
 # The shell cases that fail today, one a line: `<case> <why it fails today>`. Sorted. The kernel
 # 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: not seeded yet; seeded from a develop run after the SMLib pin bump.
+# Baseline: 45f69c0e5 with SMLib 60b1c6a, aarch64 Linux.
+cov-replace-face-step-onto-the-higher-face not supported yet: SMLib's offset of faces refuses (Unsupported) a move that closes a neighbouring face (the step wall) to nothing

tests/kernel-cases/shell/cov-replace-face-step-onto-the-higher-face/expected.json

@@ -0,0 +1,22 @@
+{
+ "sources": [],
+ "what": "the lower top of a stepped block replaced by the plane of the higher top: the step wall closes up and the tops become one face",
+ "source": "analytic",
+ "method": "stepped block (x 0..20 to z=20, x 20..40 to z=10); the lower top goes to z=20: a 40x30x20 block, V = 24000, A = 2(1200+800+600), the coplanar tops one face: 6 faces",
+ "body_count": 1,
+ "faces": 6,
+ "volume_mm3": 24000.0,
+ "area_mm2": 5200.0,
+ "bbox": {
+  "min": [
+   0,
+   0,
+   0
+  ],
+  "max": [
+   40,
+   30,
+   20
+  ]
+ }
+}

tests/kernel-cases/shell/cov-replace-face-step-onto-the-higher-face/recipe.json

@@ -0,0 +1,39 @@
+{
+ "commands": [
+  {
+   "command": "solid.box",
+   "params": {
+    "length": 40,
+    "width": 30,
+    "height": 10,
+    "body_name": "Block"
+   }
+  },
+  {
+   "command": "solid.box",
+   "params": {
+    "length": 20,
+    "width": 30,
+    "height": 20,
+    "operation": "join"
+   }
+  },
+  {
+   "command": "solid.replace_face",
+   "params": {
+    "faces": [
+     [
+      30,
+      15,
+      10
+     ]
+    ],
+    "target_face": [
+     10,
+     15,
+     20
+    ]
+   }
+  }
+ ]
+}

tests/kernel-cases/shell/cov-replace-face-top-onto-a-plane/expected.json

@@ -0,0 +1,22 @@
+{
+ "sources": [],
+ "what": "a block's top face replaced by the plane z=15",
+ "source": "analytic",
+ "method": "the top moves from z=10 to 15: a 40x30x15 block, V = 18000, A = 2(1200 + 600 + 450)",
+ "body_count": 1,
+ "faces": 6,
+ "volume_mm3": 18000.0,
+ "area_mm2": 4500.0,
+ "bbox": {
+  "min": [
+   0,
+   0,
+   0
+  ],
+  "max": [
+   40,
+   30,
+   15
+  ]
+ }
+}

tests/kernel-cases/shell/cov-replace-face-top-onto-a-plane/recipe.json

@@ -0,0 +1,37 @@
+{
+ "commands": [
+  {
+   "command": "solid.box",
+   "params": {
+    "length": 40,
+    "width": 30,
+    "height": 10,
+    "body_name": "Block"
+   }
+  },
+  {
+   "command": "solid.replace_face",
+   "params": {
+    "faces": [
+     [
+      20,
+      15,
+      10
+     ]
+    ],
+    "target": {
+     "origin": [
+      0,
+      0,
+      15
+     ],
+     "normal": [
+      0,
+      0,
+      1
+     ]
+    }
+   }
+  }
+ ]
+}