claude
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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.history.md (18 sidecars) and INDEX.history.md preserve every superseded block verbatim, stamps and issue refs intact, under a frozen-record banner. Nothing was deleted: superseded design intent remains an addressable working-tree artifact, off the per-cycle audit walk. - Ledger discipline is now stated in INDEX.md: live files are edited in place at cycle close, superseded text moves verbatim to the sidecar, and a supersession marker in a live file is itself an audit finding.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.
70 lines
3.9 KiB
Markdown
70 lines
3.9 KiB
Markdown
# C1 — Determinism and disjoint parallelism
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**Guarantee.** A backtest is a deterministic, synchronous, non-concurrent event
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loop that reaches a unique state after each input tick. Same input (incl. seed)
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→ bit-identical run. Two backtests are fully disjoint and run concurrently
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without locking. The bit-identity is *per run*: one backtest of given (inputs,
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seed) reproduces byte-for-byte. It does **not** extend to a *derived metric*
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recomputed for the same params by two *different command paths* (e.g. a swept
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member's `sqn` vs the same cell re-run under `aura generalize`), which may differ
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by floating-point reassociation (≤1 ULP) because the two paths accumulate the
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same logical reduction in a different operation order (IEEE-754 non-associativity).
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C1 governs the determinism of a single run, not the cross-command bit-identity of
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a re-derived statistic. (fieldtest 0078, ratified.)
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**Forbids.** Concurrency *within* a single sim; any nondeterministic input that
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is not captured as an explicit input (see C11, C12).
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**Why.** Real money rides on backtest results; reproducibility and an audit
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trail are non-negotiable. Speed comes from parallelism *across* sims, which
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disjointness makes lock-free.
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## Current state
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The per-run event loop is `Harness::run` (`crates/aura-engine/src/harness.rs`):
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each cycle picks the live source head with the smallest `(timestamp, source
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index)`, pops one record, increments `cycle_id`, and forwards the value —
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allocating nothing per cycle beyond a reused scratch buffer. A single run is
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fully sequential, so its output is bit-identical by construction; the
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end-of-stream `finalize` pass runs after the loop and adds no within-sim
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concurrency.
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Cross-sim parallelism spans the sweep/member/window fan-out and campaign cells
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(#277). The campaign executor `execute` (`crates/aura-campaign/src/exec.rs`)
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flattens the (strategy, instrument, window, regime) cell matrix into
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document-order `PlannedCell`s, groups them by instrument ordinal, and walks
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sequential chunks of K instrument groups — `--parallel-instruments`
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(`DEFAULT_PARALLEL_INSTRUMENTS = 4`, `crates/aura-campaign/src/lib.rs`). K is a
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structural bound on distinct resident instruments — the RAM lever for the
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external data-server's per-reference file retention (~1.4 GB per instrument on
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the reference dataset), not a pool-worker count. Within a chunk, cells run
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concurrently via `rayon::par_iter` on the process-global pool shared with the
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member/window fan-out, and results are written into document-order `slots`, so
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outputs stay byte-identical across worker counts and bounds.
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Two scheduling-dependent carve-outs sit outside the per-run bit-identity, which
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governs successful runs. On the run-fatal path (non-containable faults, e.g. a
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dead registry store) a shared `AtomicBool` abort flag latches, and the propagated
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fault is the lowest document-order fault among the cells that completed before
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the latch; the set of per-cell family lines already written by then is
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scheduling-dependent — inert, because no campaign-run record is written on that
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path and store reads are name-keyed, never line-ordered.
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Duplicate campaign instruments are refused at both the validate tier
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(`crates/aura-campaign/src/lib.rs`, a `seen_instruments` scan) and the executor's
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`preflight`: the per-cell registry family name embeds the raw instrument string,
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so name uniqueness is what keeps concurrent appends from racing one name's
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run-index assignment.
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## See also
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- [C4](c04-cycle-granularity.md) — tie determinism preserves this contract; the
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source-index tie-break is what keeps the merge order deterministic.
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- [C11](c11-sources-record-replay.md), [C12](c12-atomic-sim-unit.md) —
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recorded/pinned inputs are how nondeterministic sources become explicit inputs;
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the harness is the atomic disjoint unit.
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- [C23](c23-graph-compilation.md) — the raw-index compilation primitive; names
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survive only as non-load-bearing debug symbols.
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> History: [c01-determinism.history.md](c01-determinism.history.md)
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