engine: mesh.hex.octree command

Replaces the mesh with the octree all-hex mesh of a body, an imported surface or every body
of the open design, and tags boundary element faces with their B-rep faces so sets by
geometry resolve. Size, tolerance, refinement depth, element cap, attempts and optimiser
sweeps are validated and capped; the element cap defaults to the session limit
(`Limits::max_hex_elements`), which the hostile-params test keeps small. Body input and face
tagging are shared with mesh.hex.generate. The catalogue's Automatic Hex entry is ready.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

ROADMAP.md

@@ -32,7 +32,7 @@ pressure) is a degree of freedom of the existing DOF framework, not a separate s
 | M3 First deck | Sets and surfaces bound to SolidCraft face, edge, vertex and body names, resolved after meshing; materials (isotropic and orthotropic elastic, density) with a unit-system label and consistency check; sections (solid, shell, beam profiles) assigned by set; element formulation per region mapped to each solver; BCs (fixed, displacement, symmetry); loads (force and moment on reference points, pressure, gravity); reference points with kinematic and distributing coupling; steps (linear static, frequency) with explicit per-step load and BC tables and output presets; `model.check` naming every missing or bad item; `model.*` and `mesh.tag` commands (model definition: done); writers for Abaqus input (done: `deck.write`), Nastran SOL 101/103 (done: `deck.write`) and LS-DYNA implicit (done); the `.fieldcraft` file (text definition, binary mesh, geometry references reopened on load, journal; atomic saves, autosave and recovery; undo/redo on the journal: done) | in progress |
 | M4 Own solver and first results | Element library per docs/elements.md (1D and 2D first); Linear static and modal solver (tet4/10, wedge6, hex8, hex20; sparse direct, Lanczos), verified against analytic solutions (solver: done — `fieldcraft-fem` kernels, `fieldcraft-solver` with nested dissection, sparse Cholesky and block Lanczos, `solve.static`/`solve.frequency`/`solve.probe`, patch, cantilever, Lamé, Kirsch and beam-frequency tests; reference points with kinematic and distributing couplings and moments by master–slave constraint elimination, verified by rigid motion, clamping, Saint-Venant tension, bending and tube torsion; 1D elements I: rod2/rod3 trusses, point masses, rotary inertia, springs and dashpots in both solvers and all three decks, verified by the method of joints, the three-bar truss, spring–mass, two-mass chain and torsional pendulum frequencies, and damped decay; 2D elements: plane stress, plane strain and axisymmetric tri3, tri6, quad4 (incompatible modes QM6), quad8 with two degrees of freedom per node, centrifugal loads, `mesh.planar` 2D meshes of polygons and planar faces, verified by patch tests, Kirsch, Lamé (plane strain and axisymmetric), rotating discs and cylinders, and a plane stress cantilever; deck mapping to Abaqus CPS/CPE/CAX, Nastran membranes, LS-DYNA ELFORM 12/13); shells and beams (done: quad4 MITC4 and tri3 MITC3 flat shells with a Hughes–Brezzi drilling rotation, two-node Timoshenko beams with profile properties and orientations, six degrees of freedom at shell and beam nodes shared with solids and trusses, section forces and surface stresses, verified by shell patch tests, Navier's plate, cantilever and portal-frame beams, and the Scordelis–Lo and pinched-cylinder benchmarks); results display (done: `results.*` commands, deformed shape to scale, banded contours of displacement, von Mises, principal and component stresses with a legend, mode shapes with their frequencies and animation, probing a node by clicking it, reaction force and moment sums per set, stale results marked after an edit; explicit steps: field frames by slider or animation with contours per frame, energy histories plotted) | started |
 | M5 Structured hex | 2D quad meshing of faces (`fieldcraft-mesh::quad`: transfinite mapped meshes, free all-quad meshes of polygons with holes on prescribed boundary nodes, exact planar quad validity, shared `SizeField` and even edge divisions; done for planar faces); mapped hex of six-sided regions (trivariate TFI, curved faces) and sweep meshing (multi-level extrusions with imprinted cross-sections, revolutions, one-to-one sweeps through linking faces; interval assignment, hex8/hex20 on the geometry, B-rep face tags, `mesh.hex.generate`/`sweep`/`mapped`: done, 16 of 21 corpus parts all-hex); conforming interfaces between cells (done: `mesh.hex.blocks` meshes a part split with SolidCraft's Split Body into mapped blocks as one conforming mesh — composite faces for seams and tangent faces, interval assignment over all cells, shared faces meshed once, grading off holes and fillets, free-internal-face check; the filleted bracket in 30 cells, hex20 within 0.1 % of a fine tet10 tip deflection); sweepable cells in a conforming mesh and tet–hex transition; automatic decomposition into sweepable and mappable regions, proposed as SolidCraft splits | started |
-| M6 Automatic hex | Octree/grid-dual all-hex for any part; hex-dominant by tet recombination; polycube for blocky parts; smoothing, untangling, boundary padding, layers through thin walls; mesh editing and orphan-mesh import | planned |
+| M6 Automatic hex | Octree/grid all-hex for any part (first version: done — `fieldcraft-mesh::octree`, `mesh.hex.octree`: 3-refinement grid with conforming templates refined by curvature, thickness and narrow faces, a core cleared to a manifold boundary, feature map onto it, padding and a pillow per patch capturing every sharp curve, foldover-free fitting, certified validity, B-rep face tags; the corpus hex column and the filleted-bracket oracle case; next: transitions for concave refined regions so thin and curved parts stop over-refining); hex-dominant by tet recombination; polycube for blocky parts; layers through thin walls; mesh editing and orphan-mesh import | started |
 | M7 Assemblies, contact and friction | Needs M15. Part instances from SolidCraft occurrences; tie between non-matching meshes (mortar); implicit contact: surface-to-surface mortar and node-to-surface, penalty and augmented Lagrange, self-contact, automatic pair detection with a bounding-volume search shared with explicit contact; friction: Coulomb with stick–slip, static/kinetic, anisotropic, pressure-, rate- and temperature-dependent coefficients; contact output (pressure, slip, status); thermal contact conductance and frictional heating; wear (Archard); bolt pretension, connectors with behaviour (elastic, damped, stops, locks); amplitudes, multiple steps, restart; nonlinear steps in all three decks. Verified by Hertz (sphere and cylinder), the Cattaneo–Mindlin partial-slip problem, the sliding block, NAFEMS contact benchmarks | planned |
 | M8 Materials, explicit, shells, composites | Plasticity, hyperelasticity, damage data per solver; explicit dynamics decks (Abaqus/Explicit, LS-DYNA); midsurface shells; composite layups and material orientations, continuum shells on swept hex; hybrid (mixed u–p) hex8/hex20/tet10 for nearly incompressible materials (done); heat transfer (solids done: steady and θ-method transient conduction with flux, convection and sources, thermal strain in static steps (solids and 2D) and explicit dynamics (with plasticity), coupled temperature–displacement, `solve.heat`; deck output, 2D/shell/beam conduction planned) | started |
 | M9 Post-processing and deck readers | Results readers for public formats (Nastran OP2, LS-DYNA d3plot, Abaqus `.fil`); XY and path plots, cuts, display groups, free-body forces; deck readers that keep unknown keywords; mesh convergence studies | planned |
@@ -60,7 +60,7 @@ In progress, in this order of landing:
 
 1. Tet quality: sliver repair and Delaunay refinement to a size field, so curved and filleted parts
    (the filleted bracket) solve on tets (M2).
-2. Octree all-hex for any part (M6), the project's main meshing goal.
+2. Octree all-hex (M6): concave transitions (Schneiders' modified templates or Livesu's dual schemes) so curved and thin-walled parts mesh without filling their hull with fine cells.
 3. The analysis video regenerated with the setup's symbols (done: support, load, reference-point
    and coupling symbols in the viewport and headless renders), captions and an orbit (screenshot
    camera and the ribbon following the command: done).