Added experimental channel_spectral_velocity and duct_spectral_velocity initial-condition generators for Cartesian channels with two no-slip walls and rectangular ducts with four no-slip walls. Seeded spectral perturbations use a discrete curl, support stretched wall-normal grids, and preserve the requested bulk flux. They reuse the existing file-based velocity initialization and asset staging paths; no C solver changes or recurring perturbation injection are needed.
Extended spectra.gen and the conductor with plane_spectrum and line_spectrum tasks for initial fields and saved checkpoints. Each task transforms one selected physical plane or line along uniform periodic axes, retaining signed wavenumbers, Cartesian component energies, sample coordinates, and a Parseval check. Parallel samples are not averaged; shell spectra remain available for periodic-box cases.
Replaced the turbulent-channel example's coarse wall-modelled setup with a nominal Re_tau 180 candidate DNS startup using grid.gen and a stretched 128 x 128 x 256-cell grid. Added a spectral duct startup configuration and updated the capability registry, generated inventories, and usage documentation. These configurations are experimental: successful initialization and short runtime checks do not establish transition, sustained turbulence, or grid convergence; full-scale cluster validation remains outstanding.