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Aura/docs/design/contracts/c12-atomic-sim-unit.md
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claude 8688a60ded docs(ledger): split the design ledger into an INDEX map, per-contract live files, and history sidecars
The single-file ledger had grown to 2968 lines / ~42k tokens, mixing
current design law with accreted history: 59 cycle-stamped realization
blocks, 18 [HISTORY] passages, 22 supersession markers, and the C10 /
C22 / C24 reframe sagas layered several supersessions deep. A
code-grounding audit (31 agents, adversarially verified) confirmed 11
defects stated as current truth: stale crate homes from the C28 #288
roster split (cost nodes, PositionManagement, PositionEvent, Session),
the renamed InputSpec->PortSpec, the pre-#241 project model in C16 and
the open-threads section, a stale HarnessKind retirement deferral in
C24, and three C28-internal inconsistencies.

New shape, per the ailang precedent:

- INDEX.md stays the sole addressable entry point: foundation, external
  components, a C-id-keyed contract map (one line per contract), and
  only the genuinely open architectural threads.
- contracts/cNN-<slug>.md carries each contract's current truth only:
  Guarantee / Forbids / Why with ratified refinements integrated, plus
  a code-anchored Current state. All confirmed defects are fixed here;
  crate anchors were re-verified against the tree.
- contracts/cNN-<slug>.history.md (18 sidecars) and INDEX.history.md
  preserve every superseded block verbatim, stamps and issue refs
  intact, under a frozen-record banner. Nothing was deleted: superseded
  design intent remains an addressable working-tree artifact, off the
  per-cycle audit walk.
- Ledger discipline is now stated in INDEX.md: live files are edited in
  place at cycle close, superseded text moves verbatim to the sidecar,
  and a supersession marker in a live file is itself an audit finding.

Every contract file was verified against its old text by an independent
zero-loss pass (statement-by-statement) plus a code-accuracy spot check;
C-ids and contract titles are unchanged, so existing C-id citations in
code, tests, and issues resolve as before.
2026-07-21 16:40:36 +02:00

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C12 — The atomic sim unit and the four orchestration axes

Guarantee. The atomic unit is (frozen topology + param-set + data-window + RNG-seed) → deterministic run → metrics. Parameters are typed, ranged, runtime values injected at graph build — no recompile per param-set; the optimizer sees a generic vector of typed ranges. A bound blueprint param is that param's default: "open" means must be bound by an axis, "bound" means default, overridable by an axis, so axis 1 (param-sweep) may name a bound param — the family boundary re-opens it on the probe and on every member reload, and the axis binds it per cell; run/mc still require every param resolved (a truly open param refuses). Identity is untouched: content_id_of (crates/aura-research/src/lib.rs) and topology_hash (crates/aura-cli/src/main.rs) read the authored document, never a re-opened probe, and each member manifest records its per-cell bindings (#246, ratified 2026-07-12; the restriction this amends — axes bind only open knobs — was an implementation consequence of bind() shrinking the param surface, not a recorded decision). Raw data is shared read-only across sims via Arc<[T]> (the data-server is built for this). Four axes orchestrate the atomic unit: (1) param-sweep (grid/random), (2) optimization (argmax metric), (3) walk-forward (rolling in-sample optimize + out-of-sample test), (4) Monte-Carlo (N seeded realizations perturbing input). MC = sweep over seeds; each realization is itself deterministic given its seed.

Forbids. Baking a specific search strategy (Bayesian/genetic) into the primitive — those are pluggable policies atop the atomic unit; recompiling on a param change.

Why. A stable primitive + orchestration axes keeps "wahnsinnig schnell" (embarrassingly parallel across the unit) cleanly separated from search policy. Seed-as-input reconciles Monte-Carlo with C1. The "frozen topology" of the atomic unit is one harness instance, selected by the harness's structural axes (C20); the structural experiment matrix is the outer orchestration over this dimension, the tuning sweep the inner (C19/C20).

Current state

Harness::run is typed as a producer seam — the object-safe Source trait (peek/next, plus bounds and a resident_records() residency probe; crates/aura-engine/src/harness.rs) that the k-way merge drives (C3). Two source shapes back it. The eager load_m1_window/close_stream path (crates/aura-ingest/src/lib.rs), wrapped as VecSource, materializes a whole stream and is retained for bounded loads. The streaming M1FieldSource (crates/aura-ingest/src/lib.rs) pulls a data-server window lazily, borrowing one Arc<[M1Parsed]> chunk per pull (zero-copy within a source) and decoding each Scalar on demand, so its source ring is resident O(one chunk), not O(window length) — resident_records() is a per-source bound, not whole-process RSS.

Raw-data sharing is realized both within and across sims. The data-server's FileCache retains each window's parsed chunks read-only for the pass, so process residency is O(records-touched) — the replay-many sharing model, not a leak. Across sims, the sweep / Monte-Carlo / walk-forward families (axes 24) build their members over one shared Arc<DataServer> (one FileCache; crates/aura-ingest/src/lib.rs), so a window is parsed once and every member's M1FieldSource borrows the same cached Arc<[M1Parsed]> chunks. The single-pass parse cost of a window is tracked as #95.

Axis 1 (param-sweep) is built. GridSpace enumerates a cartesian lattice over discrete per-slot value-lists; RandomSpace draws N seeded points over typed continuous ParamRanges (I64 inclusive [lo,hi], F64 half-open [lo,hi)), validated against the param-space before any run; a ListSpace enumerates an explicit point list. All implement the Space trait the disjoint sweep / run_indexed core is generic over (crates/aura-engine/src/sweep.rs), so every enumeration runs through one execution path (C1: results in enumeration order, not completion order). The other axes are realized as families over that core: walk_forward + WindowRoller (crates/aura-engine/src/walkforward.rs) for the rolling in-sample/out-of-sample split, monte_carlo (crates/aura-backtest/src/mc.rs) for the seed sweep; optimization is argmax over a sweep's metrics, a policy atop the core rather than a baked-in strategy. The seeded sampler reuses the bit-stable SplitMix64 (crates/aura-analysis/src/lib.rs) 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).

See also

History: c12-atomic-sim-unit.history.md