mesh.plan: decomposition proposals for unmapped features

For a body with features the sweep cannot mesh, mesh.plan replies a
decomposition: the cuts that box those features into one cell, the region,
and the commands that make the cuts and mesh the cells with pyramids. A plate
with a joined dome: 5 cuts, 17 hex cells swept together, the dome cell tet,
valid and conforming, end displacement in tension within 0.4% of all-tet.

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

docs/features.md

@@ -6,7 +6,7 @@ Every entry is a toolbar button. **Ready** entries run their command; **coming s
 shown greyed with the roadmap milestone that brings them (ROADMAP.md). Scripts, the command line,
 the control channel and AI agents over MCP (docs/mcp.md) run the same commands.
 
-81 ready, 38 coming soon.
+81 ready, 37 coming soon.
 
 ## Geometry
 
@@ -40,12 +40,11 @@ the control channel and AI agents over MCP (docs/mcp.md) run the same commands.
 | 2D | 2D Mesh — Quad or triangle mesh of a planar face or polygon in the XY plane for plane stress, plane strain and axisymmetric models; edges tagged | ready | `mesh.planar` |
 | Structured Hex | Quad Faces — All-quad meshes of faces on shared edge nodes | coming soon (M5) |  |
 | Structured Hex | Hex Mesh — Structured hex mesh of a body: automatic, or extruded, swept, revolved or mapped (the Method drop-down) | ready | `mesh.hex.generate`, (`mesh.hex.sweep`), (`mesh.hex.mapped`) |
-| Structured Hex | Partitioned Mesh — One mesh of a partitioned part, a method per cell (hex, tet, or all hex as conforming blocks); cells joined across partitions | ready | `mesh.cells`, (`mesh.hex.blocks`) |
+| Structured Hex | Partitioned Mesh — One mesh of a partitioned part, a method per cell (hex, tet, or all hex as conforming blocks); cells joined across partitions, tet cells to hex cells through conforming pyramids | ready | `mesh.cells`, (`mesh.hex.blocks`) |
 | Structured Hex | Extrude to Surface — Hex layers from a meshed or planar section up to a curved target surface, following the side faces | ready | `mesh.hex.extrude` |
 | Structured Hex | Mesh Plan — A hex-meshing plan from the features that built a body (sweeps, blocks, O-grids, layers, imprints, copies); saved, editable, applied with the structured meshers | ready | `mesh.plan`, `mesh.plan.apply` |
 | Structured Hex | Mesh Block — A mapped block of hex, wedge or quad elements between corner points; projection blocking (a block topology projected onto the part) | ready | `mesh.block`, `mesh.hex.project` |
 | Structured Hex | Decompose — Find sweepable and mappable regions of 3D parts (extruded cross-sections are already cut into blocks by Hex Mesh) | coming soon (M5) |  |
-| Structured Hex | Transition — Conforming tet–hex interfaces with pyramids | coming soon (M5) |  |
 | Automatic Hex | Octree Hex — Unstructured all-hex mesh of any part: adaptive grid, boundary layers on every sharp edge, untangled and proven valid | ready | `mesh.hex.octree` |
 | Automatic Hex | Hex-Dominant — Hex-dominant mesh by recombining tets | coming soon (M6) |  |
 | Automatic Hex | Polycube — Polycube hex mesh of blocky parts | coming soon (M6) |  |

docs/meshing/literature.md

@@ -1132,6 +1132,22 @@ faces, so a region need not be sweepable between two parallel faces.
   National Conference 1968.
 - **Layer grading**: geometric progression of thicknesses (last over first = bias).
 
+### B11. Hex–tet transitions and decomposition proposals (implemented in `fieldcraft-mesh::transition`, `mesh.cells`, `mesh.plan`)
+
+- **Pyramid transition layer**: a pyramid on each quadrilateral of a hex mesh's interface with a
+  tetrahedral region, its apex inside the region, so tetrahedra share its triangular sides:
+  S. J. Owen, S. A. Canann, S. Saigal, *Pyramid elements for maintaining tetrahedra to hexahedra
+  conformability*, AMD Vol. 220, Trends in Unstructured Mesh Generation, ASME 1997, 123–129. The
+  tet mesher keeps the pyramids' sides as frozen boundary faces (A3's refinement and improvement
+  refuse to change them).
+- **Pyramid element**: L. Bedrosian, *Shape functions and integration formulas for
+  three-dimensional finite element analysis*, IJNME 35(1):95–108, 1992 (rational functions, a
+  collapsed Gauss rule).
+- **Decomposition into sweepable cells**: cutting a part so most of it sweeps and a remainder goes
+  to a free mesher, as in T. D. Blacker, *The Cooper Tool*, Proc. 5th International Meshing
+  Roundtable, 13–29, 1996 (B4, B8); here the remainder is the box round the features the
+  provenance plan does not map.
+
 ## Part C: Datasets and benchmarks
 
 | Dataset | Content | Licence | Usable for FieldCraft? |