Engine: mesh.cells meshes a partitioned part cell by cell

Each cell (a body of the open design) gets its own method: structured hex where
one fits (auto falls back to tet and says why), or tet. All go into one mesh.
Cells on either side of a partition are joined: where their element faces
match node for node the nodes are merged; otherwise (hex next to tet, or
different divisions) the two partition faces get a set each and a dual mortar
tie, the reported hex-tet transition. A 40 mm bar cut in half, one half hex,
the other tet, stretches F L / (E A) to 1e-6.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/cmd/forms.rs

@@ -700,6 +700,16 @@ pub const HEX_MAPPED: &[Field] = &[BODY, SURFACE, HEX_SIZE, HEX_ORDER, TOLERANCE
 pub const HEX_BLOCKS: &[Field] =
     &[references("bodies", "Cells", C::Body).hint("every body of the design"), HEX_SIZE, HEX_ORDER, TOLERANCE, WELD, WELD_DISTANCE, FEATURE_ANGLE];
 
+pub const CELLS: &[Field] = &[
+    json("methods", "Methods").hint(r#"{"cell": "auto | hex | swept | extrude | sweep | revolve | mapped | tet"}"#),
+    choice("default", "Other cells", &[("auto", "Auto (hex, else tet)"), ("hex", "Hex"), ("swept", "Swept"), ("mapped", "Mapped"), ("tet", "Tet")])
+        .def("\"auto\""),
+    references("bodies", "Cells", C::Body).hint("every body of the design"),
+    HEX_SIZE,
+    HEX_ORDER,
+    TOLERANCE,
+];
+
 pub const HEX_OCTREE: &[Field] = &[
     BODY,
     SURFACE,