Two-task execution plan for spec 0048: Task 1 lands the whole aura-engine/walkforward.rs cut atomically (struct shapes, walk_forward seam, param_stability rewrite, scalar_as_f64 deletion, fixture migration, new Bool-slot test) gated on a crate-only `cargo test -p aura-engine`; Task 2 threads the aura-cli caller and runs the workspace gates. Keeps a windows.is_empty() guard in param_stability to preserve the documented empty-on-no-windows contract (C1).
refs #75
Brummel
6ce00ee053