# C12 — The atomic sim unit and the four orchestration axes: history

> FROZEN HISTORICAL RECORD. Each block below was true as of its cycle/date stamp
> and may be superseded; this file is NOT current truth and NOT a grounding
> surface. Current contract: [c12-atomic-sim-unit.md](c12-atomic-sim-unit.md).

**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).

**Realization (cycle 0041).** The eager ingestion of cycle 0011 is no longer the
only path. `Harness::run` is re-typed to a **producer seam** — a `Source` trait
(`peek`/`next`, object-safe) the k-way merge drives — and a streaming
**`M1FieldSource`** (`aura-ingest`) pulls a data-server window lazily, borrowing
**one** `Arc<[M1Parsed]>` chunk per pull (zero-copy *within* a source) and
decoding each `Scalar` on demand: the **source ring** is resident O(one chunk),
not O(window length) — the measured `resident_records()` predicate, a *per-source*
bound, not whole-process RSS. (Data-server's `FileCache` retains each window's
parsed chunks read-only for the pass — ~56 B/record — so process residency is
O(records-touched); that is the **replay-many** sharing C12 wants — one window
parsed once across a sweep family — not a leak. The single-pass cost is tracked as
#95.) The eager `load_m1_window`/`close_stream` path is kept for bounded loads (the
gap closes by a streaming path *existing*, not by deleting the eager one). **Realized
(2026-06-29, family cycles shipped).** cross-*sim* `Arc<[T]>` sharing — one window shared
zero-copy across many disjoint sweep sims — is now in force: the sweep / Monte-Carlo /
walk-forward families (axes 2–4 above) build their members over **one** shared
`Arc<DataServer>` (one `FileCache`), so a window is parsed once and every member's
`M1FieldSource` borrows the same cached `Arc<[M1Parsed]>` chunks
(`crates/aura-ingest/src/lib.rs:316`). The single-pass *parse* cost stays tracked as #95.