docs: meshing literature survey and the tet/hex pipeline it chooses (#1)

Survey of about 75 papers on robust predicates, Delaunay tetrahedralization, boundary
recovery, quality improvement and hexahedral meshing, with verified DOIs and the
licence of every associated code base. Architecture and roadmap now name the chosen
methods (robust CDT after Diazzi et al. 2023; octree-dual all-hex first). ADR 0001
adds the licence findings and the test-geometry rule.


Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture.md

@@ -43,12 +43,18 @@ Rules beyond the layer order:
    so feature edges and face-based loads and BCs survive meshing.
 2. **Surface preparation.** Weld coincident vertices, check the surface is closed, manifold and
    consistently oriented, find feature edges (face boundaries, sharp dihedral angles).
-3. **Tetrahedral meshing.** 3D Delaunay tetrahedralization of the boundary points with exact
-   predicates, boundary recovery, Delaunay refinement to a size field, then Voronoi-based
-   optimization (centroidal Voronoi / optimal Delaunay) and sliver removal.
-4. **Hexahedral meshing (the core).** All-hex first where it can be guaranteed valid, with
-   hex-dominant as the fallback; the method is chosen from the literature survey
-   (`docs/meshing/literature.md`).
+3. **Tetrahedral meshing.** Bowyer–Watson Delaunay on Shewchuk's adaptive predicates (symbolic
+   perturbation for degeneracies), boundary recovery by the robust constrained Delaunay method of
+   Diazzi et al. 2023 (implicit Steiner points on indirect predicates, gift-wrapping fallback), so
+   every boundary triangle and its B-rep face tag survives. Then constrained Delaunay refinement to a
+   size field, ODT smoothing interleaved as in Tournois et al. 2009, and the Klingner–Shewchuk 2007
+   improvement schedule against slivers.
+4. **Hexahedral meshing (the core).** Octree/grid dual all-hex first, the one family that meshes
+   any input validly (Livesu et al. 2021 dual schemes, Pitzalis et al. 2021 refinement, Gao et al.
+   2019 feature projection and padding, Garanzha et al. 2021 untangling). Then hex-dominant by tet
+   recombination (Pellerin et al. 2018), then polycube (DualCube labelling) for blocky parts;
+   frame-field/integer-grid-map methods stay research. Validity uses a certified trilinear Jacobian
+   check (Marschner et al. 2020), not corner Jacobians alone.
 5. **Quality.** Scaled Jacobian, aspect ratio, dihedral angles; every generated mesh is checked
    for positive Jacobians and conserved volume before it reaches the model.