Predict ranked candidate crystal structures from a powder XRD pattern. Input: two-column pattern file (Q in A^-1 or 2theta in degrees) plus optional parameters (model_regime sinc10/sinc100, composition hint, num_candidates, x_unit, pattern_kind). Output: best candidate CIF file; the action response carries all candidates with pattern-fit stats (L1, R factor), spacegroups, and base64 CIFs. Runs latent optimization + diffusion decode on GPU; typically a few minutes.