Sweeps rig: a circle touching its axis revolved a quarter turn, as a case

The horn torus quarter (a circle r5 touching the Z axis, revolved 90 deg) is a
sweeps rig case with its Pappus volume, pi 25 x 2 pi 5 / 4 = 616.850. SMLib's
revolve refuses the profile today (status 1001), so it is on KNOWN_FAILING.

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

tests/kernel-cases/sweeps/KNOWN_FAILING

@@ -2,3 +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: not seeded yet; seeded from a develop run after the SMLib pin bump.
+cov-revolve-circle-touching-its-axis-a-quarter-turn SMLib revolve status 1001 on a profile touching its axis

tests/kernel-cases/sweeps/cov-revolve-circle-touching-its-axis-a-quarter-turn/expected.json

@@ -0,0 +1,8 @@
+{
+ "sources": [],
+ "what": "a circle r5 that touches the revolve axis, revolved 90 deg: a quarter of a horn torus, its tube pinched to a point on the axis",
+ "source": "analytic",
+ "method": "the disc r5 about (5, 0) on XZ touches the Z axis at the origin; Pappus, its centroid 5 from the axis: V = pi 25 x 2 pi 5 / 4 = 616.850275",
+ "body_count": 1,
+ "volume_mm3": 616.8502750680849
+}

tests/kernel-cases/sweeps/cov-revolve-circle-touching-its-axis-a-quarter-turn/recipe.json

@@ -0,0 +1,34 @@
+{
+ "commands": [
+  {
+   "command": "sketch.create",
+   "params": {
+    "plane": "XZ",
+    "name": "Tube"
+   }
+  },
+  {
+   "command": "sketch.circle.center",
+   "params": {
+    "center": [
+     5,
+     0
+    ],
+    "radius": 5
+   }
+  },
+  {
+   "command": "sketch.finish",
+   "params": {}
+  },
+  {
+   "command": "solid.revolve",
+   "params": {
+    "sketch": "Tube",
+    "axis": "Z",
+    "angle": "90 deg",
+    "body_name": "Horn"
+   }
+  }
+ ]
+}