Ship the random half of the C12.1 param-sweep axis (grid landed in 0028).
A new `Space` trait (`points`/`param_specs`) generalizes `sweep`/`sweep_with_threads`
from `&GridSpace` to `&S: Space`; `GridSpace`'s trait impl forwards to its existing
inherent methods, so the grid path is behaviour-preserving (C1, every pre-existing
grid sweep test stays green). `RandomSpace` is the second `Space` producer: N seeded
uniform points over per-slot typed `ParamRange { lo, hi }` ranges (I64 inclusive
[lo,hi], F64 half-open [lo,hi)), validated in `new` against the param-space — a
non-numeric slot, a range-kind mismatch, and an empty range are the three new typed
`SweepError` variants, all caught before any run. Sampling reuses the existing
bit-stable `SplitMix64` (promoted to `pub(crate)`) as a code-path-disjoint instance
from the data-edge seed RNG — the #52/#71 World-II source-seam firewall: they share
only the `u64` type, never a path. The sweep-layer signature stays param-only
(`Fn(&[Cell]) -> RunReport`); no `Source`/stream type enters it.
Deviation from the spec's verbatim sampler, accepted as a correctness hardening:
the I64 draw guards the full-width span ([i64::MIN, i64::MAX] computes a span of
2^64 that wraps a u64 to 0) and uses `lo.wrapping_add(draw as i64)` instead of a
plain `+`. This avoids both the `% 0` divide-by-zero at the full domain and the
signed-overflow panic the literal form hits on wide ranges in debug builds, while
preserving uniform-over-[lo,hi] draws and determinism (an extra RED test,
random_points_full_range_i64_does_not_panic, pins it). Modulo bias for spans not
dividing 2^64 remains the spec's documented, accepted simplification (param search
needs no cryptographic uniformity).
Includes a public-API E2E suite (tests/random_sweep_e2e.rs) exercising the feature
exactly as a downstream researcher would — reproducibility at the report boundary,
seed-sensitivity, in-range draws, the typed NonNumericRange gate, a well-formed
empty (count==0) family, and Grid/Random interchangeability through `Space`.
Verified: cargo test --workspace green (incl. 17 new engine tests + 6 E2E);
cargo clippy --workspace --all-targets -- -D warnings clean.
closes#52
Brummel
e17d78f24f