generators/grid.gen rebuilt around two composed geometries, box and sweep, replacing the three hardcoded ones (cpipe, pipe, warp).
- box is a Cartesian block whose two bounding walls may each be a piecewise height field - flat, step, ramp, arc, sine, gaussian, hill segments laid end to end, each continuing from the height the previous reached. One representation reaches the backward- and forward-facing step, sudden expansion and contraction, open cavity, rib-roughened channel, wall-mounted obstacle, periodic hill, wavy wall, ramp and diffuser - no multi-block or immersed-boundary support was added; all of this is a single warped box. A spanwise envelope scales a wall's departure from its datum, which is what gives a wall-attached obstacle finite width. box subsumes warp exactly: every shipped [warp] config section regenerates byte-identical under [box] with nothing but the section renamed, which is the proof its migration was faithful.
- sweep carries a cross-section (rectangle or the square-to-disc circle map, chosen over an O-grid because that needs a circumferential seam the runtime can only reach through an unselectable cgrid branch) along a piecewise centreline of straight and arc segments, using a parallel-transported frame so a path leaving one plane does not twist the section about its own tangent. It reproduces the retired cpipe geometry to 1.8e-15 over a domain of size 13 (arithmetic reordering, not a difference in geometry) and the 2.9 MB .picgrid examples/bent_channel used to ship to 5e-8, the precision that file was written at.
- A geometry-independent placement and similarity transform list - anchor/translate/scale/rotate/mirror/permute - composes on top of the existing origin placement, in one kind:key=value grammar shared by wall segments, path segments and transforms alike, reading identically on the command line and in a .cfg.
- Given the case's reference scales (or explicit --length-ref/--nu/--velocity-ref/ --re-tau/--u-tau), the .info report now also states the grid in solver units and nominal wall units - reproducing a shipped channel config's hand-computed y+ = 0.5, dx+ = 8.8, dz+ = 17.5 instead of leaving that arithmetic in an unchecked comment. Coordinates are never scaled by the generator; non-dimensionalization stays exactly where it already was.
- New refusals rather than silent bad output: a wall segment turning the wall in less than one cell (below that a shorter segment produces the identical single-cell jump), node counts the multigrid hierarchy cannot coarsen, one-sided stretching on a periodic axis, and rotating a grid with a periodic axis (the runtime's periodic reconstruction assumes an axis-aligned seam). An unknown config key is now an error, not a warning - it previously left the built-in default silently in force.
- Two pre-existing defects the rewrite surfaced: a single-node axis returned a bare array where every other path returns (positions, factor), breaking the caller's unpack; and Jacobian_Sign_Consistent cannot detect a uniformly inverted grid, since such a grid agrees with itself. A separate Right_Handed report catches it, and showed that the retired pipe O-grid had always emitted a left-handed mesh - not fatal, since the solver already repairs a uniformly negative Jacobian at runtime, but previously invisible in the generator's own output.
- generators/ was invisible to audit_family_census and the review-packet's change router, so a change to any of the five bundled generators named no test target and no owning page; both now see it, and grid.gen has the freshness surface that lets 48_Grid_Generator_Guide be flagged stale when the generator moves without it.
- examples/bent_channel now generates its grid instead of shipping it, and examples/decaying_isotropic_turbulence gets its own periodic-cube config instead of overriding every field of a curved-tube template through cli_args. Together with deleting a duplicate and a derived .vts that should never have been tracked, examples/ drops from 9.1 MB to 3.5 MB.
- grid.mode: grid_gen is refused for any analytical carrier flow other than TGV3D (a pre-existing, unrelated constraint), which the bent-channel conversion above ran into: pairing bent_channel with config/solvers/Analytical-UniformFlow.yml, as examples/bent_channel/guide.md has long documented, needs grid.mode: file on that specific combination. tests/smoke/run_smoke.sh's bent_analytical_uniform workflow and the guide now show the override, pointing at the one bent-duct .picgrid examples/search_robustness still ships.