Brummel
6a775f700f
`aura walkforward <bp> --axis <name>=<v>` emitted a rejected axis's diagnostic more than once (a racy 1-3x) when the grid did not resolve. `blueprint_walkforward_family` resolved the axes *inside* the per-window closure, and `walk_forward` fans that closure out across the windows in parallel — so several windows each `eprintln!` the same `BindError` and `exit(2)` before any one exit tears the process down. Axis resolution is window-independent, so it is hoisted to a single dispatch-boundary pre-flight (mirroring `aura sweep`, which validates its axes once before any member runs): the first in-sample window is resolved up front, surfacing the `BindError` exactly once; the per-window closure then resolves already-validated axes and cannot re-raise (`expect`). RED-first: cli_run.rs `aura_walkforward_emits_an_unknown_axis_rejection_once` drives the verb 20x and asserts the rejection is single every run (the emit count was racy, so a single invocation would be a flaky assertion). Surfaced by the World/C21 milestone fieldtest. closes #177 refs #170