Re-land the robustness batch on main (#6): fillets running into an earlier round go to blend_corner (any radius) instead of the same-radius undo; the lip and drilled-hole regression tests move into tests/robustness.rs with the new command ids; measuring 5000 faces is checked for its counts, its time in an ignored perf test run alone

Part of #6

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RjGw4gA5ZvKrU8MQP6sBgT

crates/kernel/src/tests.rs

@@ -1361,8 +1361,8 @@ fn boolean_of_a_body_in_pieces() {
     assert!((v - (2000.0 - 2.0 * PI * 4.0 * 10.0)).abs() < 1.0, "{v}");
 }
 
-/// Measuring a body of 5000 faces (a modelled thread is like that) stays fast and counts
-/// right: 0.8 s here, it took 13 s (a per-face recomputation of the body's size).
+/// Measuring a body of 5000 faces (a modelled thread is like that) counts right (it took 13 s,
+/// a per-face recomputation of the body's size; now under a second).
 #[test]
 fn measure_of_a_body_with_many_faces() {
     let n = 5000;
@@ -1373,9 +1373,23 @@ fn measure_of_a_body_with_many_faces() {
         })
         .collect();
     let b = extrude(&Plane::XY, &[Region2 { outer: Loop2::polygon(&pts), holes: vec![] }], 0.0, 10.0).unwrap().pop().unwrap();
-    let t = std::time::Instant::now();
     let m = measure(&b).unwrap();
-    // (A loaded build machine runs slower; the bound is loose.)
-    assert!(t.elapsed().as_secs_f64() < 5.0, "{:?}", t.elapsed());
     assert_eq!((m.merged.faces, m.merged.edges, m.merged.vertices), (n + 2, 3 * n, 2 * n), "{:?}", m.merged);
 }
+
+/// The time it takes (run alone, the suite's other tests share the machine):
+/// `cargo test --release -p solvecraft-kernel perf_measure_5000_faces -- --ignored`.
+#[test]
+#[ignore]
+fn perf_measure_5000_faces() {
+    let pts: Vec<Vec2> = (0..5000)
+        .map(|i| {
+            let a = std::f64::consts::TAU * i as f64 / 5000.0;
+            Vec2::new(20.0 * a.cos(), 20.0 * a.sin())
+        })
+        .collect();
+    let b = extrude(&Plane::XY, &[Region2 { outer: Loop2::polygon(&pts), holes: vec![] }], 0.0, 10.0).unwrap().pop().unwrap();
+    let t = std::time::Instant::now();
+    measure(&b).unwrap();
+    assert!(t.elapsed().as_secs_f64() < 1.5, "{:?}", t.elapsed());
+}