The last slice of the risk-regime structural axis. The sugar parity
(`translate_sweep` emitting `risk: vec![]`, absent-serializing) and the
real-data two-regime e2e landed in the earlier slices (the loop's self-correction
and its e2e phase), so this closes the remaining pieces:
- design-ledger note: the risk regime realizes the StopRule structural axis at
the campaign-document level — kept-separate keying, compared-not-selected (the
R-unit argument), the C18 stamp, absent-parity, and the deferred trace gap
(#212).
- clippy: `validate_campaign`'s regime check reads `k <= 0.0 || k.is_nan()`
instead of `!(k > 0.0)` (neg_cmp_op_on_partial_ord), behaviour-identical.
Full workspace suite green; clippy clean.
refs #210
Brummel
50d3db7028