Kernel rig: a symmetric surface extrude with no convention is the total distance (#9091); the per-side reading is its own case

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

tests/kernel-cases/surfaces/cov-extrude-line-symmetric-legacy-per-side/expected.json

@@ -0,0 +1,26 @@
+{
+ "sources": [],
+ "what": "a line extruded symmetric 10 as a surface with the legacy per-side convention: 10 each way",
+ "source": "analytic",
+ "method": "convention legacy_per_side gives the distance on each side: the plane y = 0, x 0..10, z -10..10, area 200, 4 free edges",
+ "valid": false,
+ "body_count": 1,
+ "faces": 1,
+ "boundary_edges": 4,
+ "area_mm2": 200.0,
+ "surface_types": [
+  "plane"
+ ],
+ "bbox": {
+  "min": [
+   0,
+   0,
+   -10
+  ],
+  "max": [
+   10,
+   0,
+   10
+  ]
+ }
+}

tests/kernel-cases/surfaces/cov-extrude-line-symmetric-legacy-per-side/recipe.json

@@ -0,0 +1,60 @@
+{
+ "commands": [
+  {
+   "command": "sketch.create",
+   "params": {
+    "plane": {
+     "origin": [
+      0,
+      0,
+      0
+     ],
+     "x_dir": [
+      1,
+      0,
+      0
+     ],
+     "y_dir": [
+      0,
+      1,
+      0
+     ]
+    },
+    "name": "S"
+   }
+  },
+  {
+   "command": "sketch.line",
+   "params": {
+    "points": [
+     [
+      0,
+      0
+     ],
+     [
+      10,
+      0
+     ]
+    ],
+    "infer": false
+   }
+  },
+  {
+   "command": "sketch.finish",
+   "params": {}
+  },
+  {
+   "command": "surface.extrude",
+   "params": {
+    "sketch": "S",
+    "curves": [
+     "l1"
+    ],
+    "distance": 10,
+    "direction": "symmetric",
+    "body_name": "Wall",
+    "convention": "legacy_per_side"
+   }
+  }
+ ]
+}

tests/kernel-cases/surfaces/cov-extrude-line-symmetric/expected.json

@@ -1,13 +1,13 @@
 {
  "sources": [],
- "what": "a line extruded symmetric 10 as a surface: surface.extrude's distance is per side (its legacy convention, kept by default), so 10 each way",
+ "what": "a line extruded symmetric 10 as a surface with no convention: the total, 5 each side of the sketch plane, as for a solid extrude (#9091)",
  "source": "analytic",
- "method": "surface.extrude without `convention` keeps legacy_per_side (crates/engine/src/cmd/features.rs, extrude_convention_tests): the plane y = 0, x 0..10, z -10..10, area 200, 4 free edges",
+ "method": "surface.extrude without `convention` reads the distance as the total (default_extrude_convention): the plane y = 0, x 0..10, z -5..5, area 100, 4 free edges",
  "valid": false,
  "body_count": 1,
  "faces": 1,
  "boundary_edges": 4,
- "area_mm2": 200.0,
+ "area_mm2": 100.0,
  "surface_types": [
   "plane"
  ],
@@ -15,12 +15,12 @@
   "min": [
    0,
    0,
-   -10
+   -5
   ],
   "max": [
    10,
    0,
-   10
+   5
   ]
  }
 }