rtx-cfd: the deformed-tip outline chooses the flat / semicircle branch against the UNDEFORMED half-thickness — at the semicircle setting the deformed tip's radius breathes by nanometres and flipped the topology (143 → 144 points) within the first steps of the P6-b ny 41 cap-12 release at every α; pin: the point count is fixed under ± 1e-6 thickness breathing at h 10 / 6.6 mm and ny 41, semicircle and flat

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01YJPeT6WA2e7YvAnS875AHL

crates/specialized/rtx-cfd/src/mesh/patch_gen.rs

@@ -952,9 +952,16 @@ pub fn cylinder_flag_outline_deformed_tip(
     let mut pts: Vec<[f64; 2]> = Vec::new();
     // 1. Top edge: from the arc's top end toward the root, along the top
     //    polyline (given tip → root) from arclength `radius` to x = x_f.
-    // The corner radius: `radius` (the semicircle) or the flat tip's.
-    let rc = tip_corner.min(radius).max(0.0);
-    let flat = rc < radius - 1e-12;
+    // The corner radius: `radius` (the semicircle) or the flat tip's. The
+    // branch is chosen against the UNDEFORMED half-thickness `t`, never the
+    // deformed tip's `radius` (which breathes by nanometres under the FEA's
+    // deformation and flipped the topology at the semicircle setting).
+    let flat = tip_corner < t - 1e-9;
+    let rc = if flat {
+        tip_corner.min(radius).max(0.0)
+    } else {
+        radius
+    };
     // Corner arc centres and the tangent points on the faces.
     let c_top = [
         tc[0] - rc * axis[0] - rc * normal[0],