audit: cycle 0049 — drift-clean (random param-sweep)

Architect drift review over 3de00e2..HEAD (the 0049 spec/plan/feat plus the
two intervening refactors that had not been audited: aura-ingest M1 transpose
6390093, aura-std SMA perf 67c1f51). Verdict: feature clean — C1 determinism
preserved (RandomSpace points seed-determined before any run; grid path
behaviour-preserving via trait-forwards-to-inherent), the #52/#71 source-seam
firewall honoured in code (sweep stays &S: Space + Fn(&[Cell]) -> RunReport, no
Source type enters the sweep layer; SplitMix64 a code-path-disjoint instance),
and both intervening refactors behaviour-preserving (pinned by
incremental_matches_full_resum_within_tolerance and
chunked_accumulation_equals_single_transpose).

Two low-grade doc-debt items found and fixed inline (doc-only, behaviour-
preserving):
- sweep.rs module doc named only the grid axis; refreshed to name RandomSpace
  + the Space trait the module now also owns.
- C12 ledger had no realization note for axis-1 (param-sweep); added one
  recording the grid (0028) + random (0049) landing and the Space-trait
  unification.

Regression gate: the project configures no regression scripts, so the test
suite + lint are the gate. Independently verified: cargo test --workspace green
(incl. the 17 new engine tests + 6 public-API E2E), cargo clippy --workspace
--all-targets -- -D warnings clean.

Drift-clean, not a milestone close (no milestone fieldtest run this cycle).

crates/aura-engine/src/sweep.rs

@@ -1,8 +1,11 @@
-//! Grid param-sweep (C12.1): enumerate a cartesian grid over a blueprint's
+//! Param-sweep (C12.1): enumerate a blueprint's param-space — either a cartesian
-//! param-space and run each point disjointly (C1). This module owns enumeration
+//! `GridSpace` (a discrete per-slot lattice) or a seeded `RandomSpace` (`N` draws
-//! (`GridSpace`), execution (`sweep`), and collection (`SweepFamily`); the
+//! over typed continuous ranges) — and run each point disjointly (C1). Both
-//! per-point run-to-metrics closure is the author's (harness-specific sink glue
+//! enumerations implement the `Space` trait that `sweep` is generic over, so
-//! the engine cannot generically own — C8/C18).
+//! either runs through one execution path. This module owns enumeration
+//! (`GridSpace` / `RandomSpace` / the `Space` trait), execution (`sweep`), and
+//! collection (`SweepFamily`); the per-point run-to-metrics closure is the
+//! author's (harness-specific sink glue the engine cannot generically own — C8/C18).
 
 use aura_core::{zip_params, Cell, ParamSpec, Scalar, ScalarKind};
 use crate::RunReport;

docs/design/INDEX.md

@@ -568,6 +568,16 @@ a streaming path *existing*, not by deleting the eager one). **Still open:**
 cross-*sim* `Arc<[T]>` sharing — one window shared zero-copy across many disjoint
 sweep sims — has no consumer until the orchestration families (axes 2–4 above:
 #66/#68/#69) are built, and remains the target for those cycles.
+**Realization (cycles 0028, 0049).** Axis 1 (param-sweep) is built. `GridSpace`
+(0028) enumerates a cartesian lattice over discrete per-slot value-lists;
+`RandomSpace` (0049) draws `N` seeded points over typed continuous `ParamRange`s
+(I64 inclusive `[lo,hi]`, F64 half-open `[lo,hi)`), validated against the
+param-space before any run. Both implement the `Space` trait the disjoint
+`sweep` / `run_indexed` core is generic over, so either enumeration runs through
+one execution path (C1: results in enumeration order, not completion order). The
+seeded sampler reuses the bit-stable `SplitMix64` as a **code-path-disjoint**
+instance from the data-edge seed RNG (the source-seam firewall, #52/#71: they
+share only the `u64` type, never a path).
 **Forbids.** Baking a specific search strategy (Bayesian/genetic) into the
 primitive — those are pluggable policies atop the atomic unit; recompiling on a
 param change.