# aura design ledger — INDEX

The ledger records the load-bearing design contracts and their rationale. Each
contract states what it **guarantees**, what it **forbids**, and **why**. A
change that breaks a contract is a design decision (amend the contract here with
its new rationale), never a silent refactor.

Provenance: contracts C1–C18 were settled in the initial rough-sketch design
interview (2026-06-03), walking the design tree root-to-leaf (C16–C18 and the
C10 refinement to a broker-independent position table came in follow-up turns;
C10 was reframed in cycle 0007 to an exposure stream, then again 2026-06-23
(#117) to a **bias** stream with signal quality in **R**, the position table a
derived layer — see C10). C19–C22 were added as the
construction / World / playground layer; C23 and the C9/C19 compilation
refinements were settled 2026-06-05 for the **Construction-layer** milestone (the
blueprint→flat-graph reading of composites and graph optimisation). C24 (the
blueprint as a serializable, World-owned data value) was settled 2026-06-29,
resolving the long-deferred #109 fork in favour of **topology-as-data** (the
game-engine principle, C16): the engine owns topology as content it serializes /
loads / generates, not as Rust source baked into the binary.
The `CLAUDE.md` **Domain invariants** section is the compressed, always-loaded
summary of the
subset that agents must never violate; this file is the fuller form with
rationale.

Vocabulary: a *contract* is one ledger entry. A *cycle* is one pipeline round; a
*milestone* is a tracker container spanning many cycles (the first milestone is
the **walking skeleton**: ingest → one signal → exposure → sim-optimal broker →
synthetic pip-equity signal-quality metric — the *pre-reframe* substrate, now
reframed to bias → R-evaluator → R-expectancy, see C10).

---

## Foundation — what aura is

aura is a framework **and** a playground for traders. A human and (primarily)
LLMs author trading **nodes** directly in Rust; the engine backtests them
deterministically and massively in parallel, composes them fractally, validates
them (sweep / Monte-Carlo / walk-forward), and freezes a validated strategy into
a standalone bot with a broker connection.

The predecessor RustAst (`myc`) tried this as a custom DSL and failed: too slow,
too buggy, and LLMs author far better in Rust than in an unfamiliar DSL. aura
inverts it — engine in Rust, strategies in Rust — but keeps RustAst's *concepts*
(synchronous reactive streams, bounded-lookback series, run-counting, SoA).
RustAst is a conceptual reference, not a dependency. The one reused component is
`data-server` (the first data source).

What sets aura apart is **not** the single backtest — every quant system does
that — but the **World**: the meta-level where harnesses are dynamically
constructed and *families* of them orchestrated and explored (walk-forward,
sweeps, Monte-Carlo, comparison). The deterministic single-harness engine is the
*substrate*; the World is the *product* (C20–C22).

---

## External components

Two sibling projects live outside this repo and are named throughout the
contracts. Their concrete location is recorded here so the repo is the single
source of truth — not session memory.

- **`data-server`** — `~/dev/libs/data-server`, Gitea `Brummel/data-server`
  (`http://192.168.178.103:3000/Brummel/data-server.git`). aura's **first data
  source** and the one reused component (Foundation; C3, C11, C12). A standalone
  leaf crate (deps: `chrono`, `regex`, `zip`) that loads Pepperstone **M1/tick**
  binary files and shares them lock-free as `Arc<[T]>` chunks
  (`CHUNK_SIZE = 1024`) via `SymbolChunkIter::next_chunk` (an inherent method
  driven by `while let`, not the `Iterator` trait); `stream_*_windowed(from_ms,
  to_ms)` provides C12's data-window with inclusive Unix-ms bounds. Records are
  **AoS** (`M1Parsed`/`TickParsed`, `time_ms: i64` Unix-ms). The ingestion
  boundary (C3) therefore **transposes** these AoS records into aura's SoA
  columns (C7) and normalizes `time_ms` → canonical epoch-ns at that one
  boundary. Pulled in as a cargo git dependency by the **`aura-ingest`** crate
  (cycle 0011) — the **data-source ingestion edge**, where the `data-server`
  external tree (and its transitive `chrono`/`regex`/`zip`) enters the workspace.
  Under the amended C16 **per-case dependency policy** (cycle 0029), `aura-ingest`
  is no longer a zero-dep *firewall* for the rest: the engine crates link
  standard vetted crates where they earn their place (e.g. `serde`/`serde_json`
  for the run registry, cycle 0029), with particular scrutiny for the frozen
  deploy artifact (C13). Consequence: `cargo build/test --workspace` resolves
  from a populated cargo cache (a Gitea fetch for `data-server` + crates.io for
  the standard crates) rather than fully offline.
- **RustAst (`myc`)** — `~/dev/RustAst`, Gitea `Brummel/RustAst`
  (`http://192.168.178.103:3000/Brummel/RustAst.git`). The predecessor DSL attempt
  (Foundation): **a conceptual reference, never a dependency** — its DSL authoring
  surface and `Value`/HM-inference machinery are exactly what aura rejects (C17).
  But its **`src/ast/rtl/` layer is a working reference implementation of the very
  streaming substrate aura rebuilds**, and is worth reading before authoring
  `aura-core` — these are not just concepts, they exist as code:
  - `rtl/series/data.rs` — `RingBuffer<T>` with financial-style indexing (index 0
    = newest), `total_count` (the **run-count** of C5) and `lookback_limit` (C8's
    pre-sized window); the `ScalarValue` marker trait ("flat scalars only, no
    String/Record" = C7's closed scalar set); `ScalarSeries<f64|i64|bool>` and the
    **SoA** `RecordSeries` for composites (C7's "OHLCV = a bundle of base columns").
  - `rtl/series/mod.rs` — `create_typed_series`, dispatching element type → storage
    backend (the type-specialized **factory** of C19).
  - `rtl/streams/mod.rs` — `Signal { cycle_id, value }` (C4's cycle clock) and the
    `Stream` / `Observer` / `ObservableStream` push traits (the reactive model of
    C4/C5).
  - `rtl/streams/register.rs` — the RTL **"register" / delay node** (the one
    explicit feedback path of C5/C9) plus a seeded, reproducible OHLC generator
    (C12's seed-as-input).

  aura reimplements these natively and **sharpens** them: types are monomorphized
  and edges type-erased to the four scalar kinds with direct dispatch (C7) instead
  of carrying boxed `Value`s, and input history is shared zero-copy as `Arc<[T]>`
  (C12) instead of a `VecDeque<Value>`. RustAst shows the *shape*; aura makes it
  fast and deterministic.

---

## Contracts

### C1 — Determinism and disjoint parallelism
**Guarantee.** A backtest is a deterministic, synchronous, non-concurrent event
loop that reaches a unique state after each input tick. Same input (incl. seed)
→ bit-identical run. Two backtests are fully disjoint and run concurrently
without locking.
**Scope (ratified, fieldtest 0078).** The bit-identity is *per run* — one backtest
of given (inputs, seed) reproduces byte-for-byte. A *derived metric* recomputed for
the same params by two *different command paths* (e.g. a swept member's `sqn` vs the
same cell re-run under `aura generalize`) may differ by floating-point reassociation
(≤1 ULP), since the two paths accumulate the same logical reduction in a different
operation order (IEEE-754 non-associativity). This is not a C1 violation: C1 governs
the determinism of a single run, not the cross-command bit-identity of a re-derived
statistic.
**Realization note (2026-07-16, #277).** Cross-sim parallelism now also spans
campaign cells: the executor flattens the cell matrix, groups it by instrument
ordinal, and walks sequential chunks of K instrument groups
(`--parallel-instruments`, default 4 — a structural bound on distinct resident
instruments, the RAM lever for the external data-server's per-reference file
retention); within a chunk, cells run concurrently on the process-global rayon
pool shared with the member/window fan-out. Results are collected into
document-order slots, so outputs stay byte-identical across worker counts and
bounds. Two deliberate scheduling-dependent carve-outs, both outside this
contract's per-run bit-identity (which governs successful runs): on the
run-fatal path (non-containable faults, e.g. a dead registry store) the
propagated fault is the lowest document-order fault among the cells that
completed before the abort flag latched, and the set of per-cell family lines
already written by then is scheduling-dependent — inert, because no
campaign-run record is written on that path and store reads are name-keyed,
never line-ordered. Duplicate campaign instruments are refused at both the
validate tier and the executor's preflight: the per-cell family name embeds
the raw instrument string, so uniqueness is what keeps concurrent appends from
racing one name's run-index assignment.
**Forbids.** Concurrency *within* a single sim; any nondeterministic input that
is not captured as an explicit input (see C11, C12).
**Why.** Real money rides on backtest results; reproducibility and an audit
trail are non-negotiable. Speed comes from parallelism *across* sims, which
disjointness makes lock-free.

### C2 — Causality / no look-ahead
**Guarantee.** A node sees only the past. Input history is a read-only window
that ends at the current cursor; a resampler emits a bar only once it is
complete.
**Forbids.** Any node access to data with `timestamp > now`; emitting a partial
/ still-forming bar.
**Why.** Look-ahead is the cardinal backtester bug — a fast backtester that
leaks the future is worse than none. Making the future *physically absent* from
what a node receives beats merely discouraging it.

### C3 — One merge, at ingestion only
**Guarantee.** Heterogeneous timestamped sources are k-way-merged by timestamp
into one chronological cycle stream at the ingestion boundary; source-native
time units (e.g. data-server's Unix-`time_ms`) are normalized there to the
canonical epoch-ns `timestamp` of C7.
**Forbids.** Any merge / as-of join *inside* the graph.
**Why.** A single ordered timeline is the mechanism that makes heterogeneous-rate
sources (news daily-bias + M5 + ticks) causally combinable without leaking the
future. Keeping the merge at one boundary keeps the graph semantics simple.

### C4 — Cycle granularity
**Guarantee.** The clock is data-driven: one input record = one cycle, advanced
in global timestamp order, with a monotonic `cycle_id`. Ties (same timestamp,
multiple sources) break by source declaration order.
**Forbids.** A fixed time-grid clock; nondeterministic tie ordering.
**Why.** The market *is* an irregular event sequence; a grid is arbitrary and
either wastes empty cycles or clumps ticks. Backtest and live differ only in the
origin of records, not the cycle semantics. Tie determinism preserves C1.

**Realization (#275, 2026-07-15).** Ingestion sources are supplied to `run` **by
role name**, not by list position. `SourceSpec` carries a `role: Option<String>`
(the bound `Role`'s name, load-bearing for source binding), and `Harness::run_bound`
resolves a keyed supply against those roles, emitting sources in `SourceSpec`
declaration order. The C4 tie-break stays "source declaration order" — now
independent of how the caller orders the supply — and a mis-bound feed is a named
`SourceBindError` at start time rather than a silently wrong run. The raw-index
`run(Vec)` primitive (positional, C23) is unchanged; every hand-built graph keeps
`role: None`.

### C5 — Freshness-gated recompute and sample-and-hold
**Guarantee.** The `cycle_id` advances everywhere (a cheap counter), but a node
re-evaluates only when ≥1 of its own inputs is fresh this cycle (detected by
run-count); otherwise it holds its last output. Stale inputs contribute their
last (held) value.
**Forbids.** Recomputing every node every cycle ("push all" is true for the
*clock*, not for *recompute"); treating a held value as missing.
**Why.** Total recompute does not scale to many sparse high-frequency sources;
freshness-gating is the performance discipline that keeps the synchronous model
fast.

### C6 — Firing policy A and B, per input group
**Guarantee.** A node declares, per input group, one of two firing policies:
**A** fire-on-any-fresh + hold (latest / as-of join — e.g. tick × held
daily-bias); **B** all-fresh barrier (synchronizing join — e.g. O/H/L/C from
four separate 15m sources: the candle is complete only when all four are fresh).
A single node may mix an A input and a B group.
**Forbids.** A single global firing mode; forcing per-node-only granularity.
**Why.** Both are genuinely needed; RustAst implemented only B. Per-input-group
granularity is required by the OHLC-plus-bias case where one node needs both.
**Realization (cycle 0004).** Firing is tagged per input — `Firing::{Any,
Barrier(u8)}` on `InputSpec` — and inputs sharing a `Barrier` id form a group; a
mode-A input is its own trivial group, so "per input group" and the per-input tag
coincide. The barrier's synchronization token is the cycle **timestamp**, not the
`cycle_id`: under C4 four same-timestamp sources are four distinct cycles, so
RustAst's `cycle_id`-equality barrier could never fire across them. A group fires
when every member's last push carries the current cycle's timestamp, guarded by
"≥1 member fresh this cycle" (so a group completed earlier does not re-fire). This
fires both the multi-source bar and the within-source diamond rejoin (every push
in a cycle carries that cycle's timestamp).

### C7 — Four scalar base types, streamed as SoA
**Guarantee.** Only `i64`, `f64`, `bool`, `timestamp` (newtype over i64,
epoch-ns UTC) are streamed, as columnar Structure-of-Arrays. Composite streams
(OHLCV) are bundles of base columns — this is the **node-output model** too: a
node emits a record of 1..K base columns (C8), each forwarded field-wise to a
consumer slot; the bundle is structural, never a fifth scalar type. Edges are
type-erased to these four kinds;
the type check is paid once at wiring/sim-start, then the topology is frozen per
sim → direct dispatch, no per-event allocation.
**Forbids.** Streaming non-scalars (String, Records, tables, calendars) — those
live as metadata beside the hot path; `dyn Any` payloads; per-event heap
allocation; topology mutation mid-sim.
**Why.** Maximal streaming performance (SIMD/cache) needs a tiny closed scalar
set and SoA. The open set is composites (schemas of columns), not scalar types.
Type-erasure at the edge is also forced by the cdylib boundary (C13).
**Realization (`Cell` carrier split, 2026-06).** The streamed value is now split
into a tag-free 64-bit word and its kind. `Cell` (`crates/aura-core/src/cell.rs`)
is a type-erased `u64`: constructed per base type (`from_i64/f64/bool/ts`) and
read only by naming the type at the call site (`i64()/f64()/bool()/ts()` —
branch-free bit-casts). The kind is therefore resolved once at the boundary and
the value itself carries no tag — C7's "the type lives at the column/edge, not in
the value" made explicit on the single-value carrier (and a single 8-byte word
vs. the 16-byte tagged enum). `Scalar` becomes `{ kind: ScalarKind, cell: Cell }`
— the self-describing form for the *dynamic* boundaries (builder binding, serde,
rendering) — with `debug_assert`-guarded native accessors (caller asserts the
kind; free in release) and a hand-written **value** `PartialEq` that preserves
the former enum's IEEE-754 semantics (`NaN != NaN`, `+0.0 == -0.0`), pinned by
the `scalar_eq_is_value_not_bitwise` fixture. Behaviour-preserving.

**Realization (`Cell` becomes the hot-path carrier, 2026-06, #74).** The carrier
swap deferred above has landed: `Node::eval` now returns `Option<&[Cell]>` and
every node out-buffer is `[Cell; N]`, so the inter-node forward carries tag-free
8-byte words. The kind lives only at the schema/column: the harness forwards each
field via the new branch-free `AnyColumn::push_cell` (infallible — the edge
kind match is verified once at bootstrap, the surviving guard
`bootstrap_rejects_*_kind_mismatch`). `Scalar` remains on the self-describing
dynamic boundaries: the param plane (`build`/`bind`/`compile_with_params`/sweep
points/`RunManifest`), `AnyColumn::get` (the type-erased read for sinks/serde),
and source ingestion (`Source::next`, the heterogeneous C3 merge). The removed
per-value runtime kind check on node output is the same authoring-bug class C8
already leaves to a `debug_assert` (output width); node-output-kind correctness
is the node's declared `FieldSpec` contract, caught by each node's own test.
Behaviour-preserving (C1).

### C8 — The node contract
**Guarantee.** A node has a **signature** — its `NodeSchema`: each input's scalar
type and firing group, its output record, **and the node's own tunable parameters —
typed, with ranges**, which aggregate into the blueprint's param-space the optimizer
sweeps (C12/C19/C20). The signature is **declared pre-build on the value-empty
recipe** (C19), so the whole interface is legible without building (cycle 0024).
The built node implements `lookbacks()` — the per-input buffer depth, the one
quantity that may depend on an injected param (e.g. an `Sma`'s window = its
`length`), read once at bootstrap to size the windows — and `eval(ctx) ->
Option<&[Cell]>`. The
engine provides read-only, zero-copy windows into each input's SoA ring buffer
(`ctx.f64_in(x)[k]`, sized at wiring); a node may *additionally* keep its own
mutable series for derived/intermediate state. `None`/Void return = filter /
not-yet-warmed-up. A node is a **producer, a consumer, or both**: a
producer/transformer exposes **one output port**, whose payload is a **record of
1..K base-scalar columns** (a scalar is the degenerate K=1 record; an `eval`
returns a borrowed row, one value per column); a **pure consumer (sink)** — chart,
equity, logger — has **no** output. Sources are pure producers; sinks are pure
consumers.
**Forbids.** A node sizing/growing its input lookback at runtime; more than one
output **port** per node; a fifth scalar type or a heterogeneous output payload
(a record is a bundle of base columns, C7); copy-on-read of input history.
**Why.** Engine-provided windows mean LLM-authored code cannot mis-manage
lookback bookkeeping, and history passes through zero-copy. Fixed, pre-sized
buffers suit deterministic, pre-dimensioned sims (no realloc in the hot loop).
**Realization (cycle 0005).** `NodeSchema.output` is a `Vec<FieldSpec>` (named base
columns; length 1 = scalar). Binding is **field-wise only**: `Edge::from_field`
selects one producer column per edge; consuming a whole record is N edges (no
"bind whole record" mechanism). The K fields of one record are **co-fresh by
construction** (one `eval`, one timestamp), so C6 is untouched. `eval` returns
`Option<&[Cell]>` — a borrowed row into a node-owned buffer — so the forward
path allocates nothing per cycle (C7) (the carrier is now a tag-free `Cell` — see
the C7 carrier note).
**Realization (cycle 0006).** The pure-consumer (sink) half of this contract is
now realized at the substrate: **recording is a node role, not a type.** A
recording node reads its typed input windows + `ctx.now()` in `eval` and pushes
the record to a destination it holds as a field (a channel, a chart handle) — an
**out-of-graph side effect**. There is no `Sink` type, trait, or engine flag: a
node that only records returns `None` (pure consumer), and a node may record
**and** return an output the engine forwards in the same `eval` (the "both"
case). **Encoding & return contract.** A pure consumer declares `output: vec![]`
— the empty record *is* the sink declaration; there is no separate type, trait,
or marker. Its `eval` returns `None` or a zero-width `Some(&[])`, and the run
loop debug-asserts the returned row's width equals the declared output width
(`row.len() == schema.output.len()`). Field-wise wiring resolves
`Edge::from_field` against the producer's `output` at bootstrap, so no edge can
bind a field of a zero-output node — it fails with `BadIndex` — making a sink
structurally unwireable as an in-graph producer; its only output is the
out-of-graph side effect. In-graph routing stays engine-owned data (the edge table); the escape out
of the graph is the node's own side effect — and that boundary is the
determinism / graph-as-data boundary (C1/C7).

**Refinement (cycle 0070 — end-of-stream `finalize` lifecycle, 2026-06-25).** The
node contract gains a second lifecycle phase beside `eval`: `finalize(&mut self)`,
a **default-no-op** trait method the engine calls **once per node, in topological
order, after the source loop drains** (the `Harness::run` epilogue). It lets a sink
**fold online** — accumulate per `eval` into O(trades)/O(1) owned state and flush
one compact summary at stream end — instead of pushing a record every fired cycle
into an unbounded channel that buffers O(cycles) rows until the run ends (the
retention BLOCKER #138 hit: a full-history Stage-1 sweep held ~2 GiB/member over
~5.5M one-minute bars). C1/C7/C8 are preserved: `finalize` runs once *after* the
deterministic event loop, adding no within-sim concurrency (C1); a folding sink
holds only owned accumulator state, no interior mutability (C7); it still declares
`output: vec![]` and its flush is the same out-of-graph side effect (C8) — one
summary row, not a per-cycle stream. Realized by `GatedRecorder` (emits only gated
rows + the genuine final row) and `SeriesReducer` (folds one column, emits one
summary row), aura-std siblings of the per-cycle `Recorder`, which survives for the
live / `--trace` / test-tap path. The recording sink's *own* per-cycle allocation
(the `Recorder`→`Probe` rename + its accumulate-vs-stream choice, #77) stays open;
`finalize` is the "non-channel exit from the graph" that issue's
accumulate-then-read option named as missing.

**Refinement (Construction-layer milestone — render labels, 2026-06-05).** A node
additionally exposes `label() -> String`, a **single-line, non-load-bearing**
render symbol: a default trait method the run loop never calls (wiring is by
index, C23). Overrides carry the node's identifying params (`SMA(2)` vs `SMA(4)`)
so a graph render (C9 graph-as-data, #13) disambiguates identical node types and
surfaces a mis-wiring. Like `FieldSpec.name`, it is an informative debug symbol,
not part of the C8 dataflow contract — adding it changes no run behaviour.

**Realization (cycle 0015 — param declaration).** The tunable-parameter half of
this contract is now realized: a node declares its knobs in `schema()` as
`params: Vec<ParamSpec>` (`ParamSpec { name: String, kind: ScalarKind }`), and
`Composite::param_space()` (cycle 0024; was `Blueprint::param_space()`) aggregates
them into one flat, path-qualified list — a
read-only projection of the graph-as-data (C9), mirroring the inline order
(C19/C23) so a param's slot matches the later flat-node order. Two refinements to
the guarantee's "typed, with ranges": (1) the declaration carries `name` + `kind`
only — the **search-range is the run's, not the node's** (which subset / grid a
sweep covers is an experiment axis, #32/C20; the node declares the knob's existence
and type, never its search interval). (2) Identity is **positional** (the slot,
C23 "by index, not name"); the path-qualified `name` is a non-load-bearing debug
symbol (like `FieldSpec.name`) — uniqueness is at the slot. **Refinement (cycle
0032):** identity in the **flat graph** stays positional (C23, unchanged), but the
`param_space()` **name projection** — the authoring / by-name address space (the
surface a sweep axis or single-run binding addresses) — must be **injective** for a
blueprint to compile (a duplicated path is unaddressable; see C9). Two layers:
positional wiring below (the flat graph), an injective name address space above (the
authoring boundary). So same-type siblings in one composite no longer silently
share a name — they must be `.named(...)` apart, which is also what disambiguates a
same-type fan-in (C9). A vector knob (`LinComb.weights`) expands to `N` flat
`weights[i]` entries, `N` topology-fixed (C19). Permitted kinds are `i64`/`f64`/
`bool` (a `timestamp` knob is a structural axis, C20, never a numeric sweep param).
Binding a value to a slot landed in cycle 0016 (#31, see C19/C23); enumerating a
sweep (#32) is the deferred next layer. The 0016 binding also moved the param
declaration's *authoring* home into the value-empty recipe, whose `params()` is read
pre-build. In 0016–0023 the built node's `schema().params` still reported the same
slots, kept in lockstep by a per-node test (a duplication filed as debt, #36); **cycle
0024 dissolved this** — the signature is declared *once* on the recipe and the built
node no longer carries `schema()` (#36 closed). See the C8 cycle-0024 realization.

**Realization (cycle 0024 — the signature lives in the blueprint, #43/#36).** The
node's whole declared interface — its `NodeSchema` (input scalar types + firing,
output record, params) — now lives **once**, on the value-empty recipe
`PrimitiveBuilder` (ex-`LeafFactory`), read pre-build by `param_space()`, the
compile-time structural validation, and the render. This closes two debts: **#43**
(a value-empty recipe used to declare *no* input/output interface pre-build — only
params) and **#36** (params declared twice, recipe vs built node, kept in lockstep
by a per-node test — those 8 tests are deleted, the duplication structurally gone).
The split that makes this work: a node's signature is **fully static** per blueprint
(input kinds/firing, output fields, params — verified across the roster; a variable-
arity node like `LinComb` takes its arity as a *recipe argument*, not an injected
param), so it can be declared without building; the **one** param-dependent quantity,
an input's buffer **lookback** depth, is no longer in the signature but answered by
`Node::lookbacks() -> Vec<usize>`, read only by bootstrap to size the windows.
`Node::schema()` is therefore **removed** — the signature is pre-build data, not a
built-node method. `BlueprintNode::signature()` answers uniformly for both arms (a
primitive returns its recipe's schema; a composite *derives* it from the interior:
role kinds in, re-exported field kinds out, aggregated params), so "every node has a
signature in the blueprint" holds for composites too.

**Realization (cycle 0027 — name input ports, refs #21/#51).** `PortSpec` now
carries a `name: String` (it drops `Copy`, like `ParamSpec`), so an input port is
named just as `FieldSpec.name` (output) and `ParamSpec.name` (param) already are.
The name is **non-load-bearing** (C23): wiring stays positional by slot, bootstrap
and the run loop never read it; it exists for tracing / graph rendering (#13). Leaf
primitives declare their slot names (`SimBroker`'s `exposure`/`price`, etc.);
`derive_signature` carries a composite's `Role.name` into the derived input port,
so the graph model (`model_to_json`) is homogeneously named across inputs, outputs,
and params and across both graph levels. This does **not** close #21 (a swapped
same-kind wiring is still only kind-checked) — it makes those slots
self-documenting; a name-consuming validation is its own future cycle.

**Realization (2026-07-11 — composite `doc`, #125).** `Composite` carries an
optional authored rationale `doc: Option<String>` — the prose twin of its `name`
and the same C23 category: a non-load-bearing debug symbol. Authored via
`Composite::with_doc` / `GraphBuilder::doc`; persisted as a Tier-1
additive-optional `CompositeData` field (no format-version bump; absent-field
documents keep their exact bytes, so existing content ids are untouched);
**blanked in the identity projection** (`strip_debug_symbols`) while staying
canonical-byte-bearing; dissolved at inline like the name (never reaches
`FlatGraph`). Surfaced read-only (C22): the graph model emits an optional
trailing `"doc"` fragment per scope (`json_str` hardened for multi-line free
text — `\n`/`\t`/`\r` named, other control chars as `\u00XX`), the viewer shows
it in both composite view states (collapsed tooltip, expanded cluster frame) and
the root's as a muted header line. The construction op-script vocabulary
deliberately has no doc-carrying surface yet (scope cut recorded on #125).

**Realization (cycle 0040 — wiring totality: every input slot connected exactly
once, #65).** The node contract's "the engine provides a window into each input"
presupposes each input is actually fed; until now an unwired interior input slot was
accepted and bootstrapped to a silent empty column (`harness.rs`), and two producers
into one slot — ill-formed, since a slot holds one column — was likewise
uncompiled-against. Cycle 0040 makes a valid graph **total and single-valued** over
its interior input slots: `check_ports_connected` (in `validate_wiring`, run at every
nesting level) requires every interior node's every declared input slot to be covered
by **exactly one** wiring act — one interior `Edge { to, slot }` or one role
`Target { node, slot }`, edges and role targets counted uniformly. Zero coverage is
`CompileError::UnconnectedPort`, more than one is `CompileError::DoubleWiredPort`. A
composite's **own** input roles (`source: None`) are coverage *providers* — the
wired-by-enclosing boundary, the root case already guarded by `UnboundRootRole` —
never consumers, so only interior input slots are subject to the rule. There is **no
optional-input concept**: every declared input port is required (no shipped node runs
meaningfully without one; an unwarmed mode-A input is *wired-but-not-yet-valued*, not
unwired). The check is **index-based and name-free** — it touches no name machinery
and emits nothing into the flat graph, so C23 is untouched (it proves the existing
raw-index wiring is total and single-valued). Inherited identically by the raw
`Composite::new` path and the `GraphBuilder::build()` path (both compile via
`compile_with_params`).

### C9 — Fractal, acyclic composition
**Guarantee.** A composite is itself a `Node` that wires a sub-graph and exposes
one output; signal, combined signal, and (with execution) strategy are all the
same abstraction, nestable arbitrarily. The dataflow graph is a DAG; the only
feedback path is an explicit delay/state node (the RTL "register"). Wiring is
written in Rust (builder API); the built graph is introspectable runtime data.
**Forbids.** Implicit dataflow cycles (combinational loops); special-casing
"signal-of-signals" as separate mechanics.
**Why.** Self-application of one contract gives unlimited composition with no
adapter zoo. Acyclicity keeps the synchronous reactive model well-defined;
forcing feedback through a visible delay node keeps the per-cycle determinism
intact and the one legitimate feedback path explicit. Graph-as-data enables
visualization, freezing, and re-parameterization for sweeps.
**Refinement (Construction-layer milestone, 2026-06-05).** "A composite is itself
a `Node`" is an **authoring-level** identity: a composite declares the same
interface (typed inputs + ≤1 output, C8) and is wireable wherever a node is, but it
is **not** a runtime object. The bootstrap **compiles it away by inlining** its
sub-graph into the one flat instance (C19/C23): the composite *boundary* dissolves
into the raw index wiring the run loop already consumes, and names stay
**non-load-bearing** (informative debug symbols only, as `FieldSpec.name` already
is). So "nestable arbitrarily" and "graph-as-data" hold at the **blueprint
(source)** level; the running graph is the flat, index-wired **`FlatGraph`**. The earlier reading — *a composite survives as a `Box<dyn Node>`
driving a nested sub-engine* — is **explicitly rejected**: it would keep the
interior opaque to the cross-graph optimiser (C23) and add a runtime sub-loop the
flat model does not need. Inlining is what makes the composite boundary free.
**Realization (cycle 0018 — composite multi-output record, #40).** "Exposes one
output" is one output **port** carrying a **record of 1..K re-exported fields**, not
one field: `Composite.output` is a `Vec<OutField { node, field, name }>` (was a
single `OutPort`). Each entry is a **named projection** of one interior
`(node, output-field)`; a consumer selects which re-exported field it reads via the
same `Edge::from_field` that already binds leaf record columns (C8 realization,
cycle 0005). This is the **same arity** C8 already grants a leaf (OHLCV = one port,
5 columns): a multi-line indicator (MACD = macd/signal/histogram) is **one** record
of K fields, **one** port, **one** row per `eval` — C8/C7/C4 untouched, a boundary
completion, not a contract change. A strategy composite is simply the K=1 case
(one bias field, C10). The re-export **names** are **non-load-bearing** (C23):
they live at the blueprint boundary and in render (cycle 0022/#46 folds each onto
its producing node as a `name := …` binding; originally `[out:<name>]` markers, #13)
but are dropped at lowering — `ItemLowering::Composite.output` is `Vec<(usize,
usize)>`, raw index pairs only, so the flat graph is name-free (verified: the
compiled-view render stayed bit-identical across this change).
**Realization (cycle 0019 — name the composite boundary, #41; param-overlay retired,
cycle 0031).** The named-projection shape covers the surviving boundary edge-kinds:
`input_roles` is a `Vec<Role { name, targets }>` (was a bare `Vec<Vec<Target>>`),
alongside `output: Vec<OutField>`. Each is an ordered, positionally-indexed
**named projection** of interior handles. **Param projection is no longer a
composite overlay** (the index-addressed `ParamAlias` was retired in cycle 0031):
a node's surface param name flows from its own **instance name** — every node
carries a name (default = its lowercased type label, override via `.named()`), and
`param_space()` is uniformly `<node>.<param>` at every level including the root. A
same-type fan-in is distinguished by naming the colliding legs, the same single act
that qualifies their param paths. Like the output and role names, **node names are
non-load-bearing** (C23): they live at the blueprint boundary and in render but are
dropped at lowering — the flat graph is wired by raw index. The full composite
boundary signature (named inputs, multi-outputs) and the per-node param path are
legible without changing the flat graph.
**Refinement (param-namespace injectivity, cycle 0032; supersedes the fan-in
distinguishability check).** A blueprint compiles only if its `param_space()` name
projection is **injective** — every path-qualified knob name is unique. A duplicated
path is a knob no binding can select alone (it has no distinct by-name address,
C12/C19), so it is a `CompileError::DuplicateParamPath` carrying the offending path;
the cure is to give the colliding same-type sibling nodes distinct names with
`.named(...)`, the same single act that qualifies their param paths. The
param-bearing indistinguishable fan-in is *one instance* of a duplicated path (two
default-named same-type legs share a leaf path). `signature_of`, `leaf_has_param`,
and the fan-in-specific check (`check_fan_in_distinguishability` /
`check_composite_fan_in`) are **retired** (cycle 0032), replaced by one structural
`check_param_namespace_injective` over the `param_space()` names, run before name
resolution in `compile_with_params` and both binders — so the canonical by-name
author sees the structural cure rather than a downstream `AmbiguousKnob` symptom
(that `BindError` arm is retired too: an injective space can never multi-match).
Paramless interchangeable same-name sources stay legal (no path, no duplicate).
The old signature-collision predicate had extra breadth — it also rejected an
**asymmetric param/paramless** collision and a **role-vs-leg** collision, *neither*
a path duplicate (each colliding configuration keeps a unique param path, or none).
That breadth guarded **render identity**, dead since the renderer was retired in
0026; both extra rejections are **intentionally dropped**. A future node-/wiring-name
distinguishability check, if ever wanted (e.g. for the WASM graph view's #21
thread), is decoupled from param-space injectivity. Construction-phase only; the
flat graph stays name-free (C23).
**Refinement (2026-06-29 — graph-as-data round-trips both ways, C24).** "The built
graph is introspectable runtime data" is now contract-level **bidirectional**: a
blueprint is not only *emitted* as data (`model_to_json`, the render half) but is
itself a **serializable data value with a load path** (data → blueprint →
`FlatGraph`), so topology is a value the World generates, stores, and reproduces —
see C24. The Rust builder API stays the primary *human / LLM* authoring surface
(C17); the data form is the *machine* surface the World owns. (Load path **realised**
cycle 0087 / #155, `d5602ec`: `aura-engine::blueprint_from_json`.)

### C10 — Strategy output is a bias stream; signal quality is measured in R; cost is a composable downstream graph (gross R → net R); money is decoupled to the live deploy edge
**Guarantee.** A strategy's primary, backtestable output is **not** an equity
curve, **nor a position-event table**, **nor a position size**, but a **bias
stream**: the DAG expresses exactly one *state* at time t (C8 — a node emits at
most one record per `eval`), so a strategy emits one **signed, bounded bias**
`f64 ∈ [-1, +1]` per cycle (per instrument) — the **sign is direction, the
magnitude is conviction**, and conviction is optional (a bare ±1 / 0 is the modal
case). Bias is **unsized**: position sizing and the protective stop do **not**
live in the strategy. The chain is `signals (scores) → decision node → bias
stream`.

**Risk-based execution is a decoupled downstream layer; in research it is Stop +
position-management in R, no Sizer.** Turning a bias into a tracked trade is the
job of a downstream **execution** chain, never the strategy's. The **stop-rule**
sets a protective stop, which **defines the risk unit R** (1R = the loss taken if
stopped). In the research loop the executor is **stop-rule → position-management**,
operating **directly in R**, with the **Veto** an optional documented pre-trade-gate
seam (a pass-through identity DCE'd away under C19/C23 when absent): there is **no
Sizer**. Sizing in *currency* (`size` / `volume`) is a **deploy** concept. C8's
wiring totality (cycle-0040 `check_ports_connected`: no optional-input concept —
every declared port is covered by exactly one wiring act) forbids a *dangling*
`size` port, so the resolution is concrete: research `PositionManagement` either
**drops its `size` input port** from its node signature, or has that port **driven
by a constant unit node** (the flat-1R degenerate) — never an unwired "vestigial"
port; the record's `size` field is held at unit and carries no research
information, and the position-event table's `volume` column likewise. Consequently
the **position-event table is demoted to a deploy / reconciliation artifact** (real
volume lives there), no longer a research artifact and no longer "fed to a broker".
The three-way decoupling of **direction (bias) / sizing / fill** stands as a
*structure*; sizing and fill are simply pushed entirely to the deploy edge, out of
the research loop.

**Signal quality is measured in R — gross R and net R.** A downstream
**R-evaluator** consumes the executor run and integrates the per-trade R-outcomes
into an **R-expectancy** / R-curve: the account- and instrument-agnostic yardstick
for *"how much R out per 1R risked?"*. R, not pips, is the unit (pips are not
risk-normalized). Two readings of the same unit: **gross R** (signal only) vs **net
R** (after the cost model), with `net R = gross R − cost-in-R`. The headline
artifact is the **net-R equity curve** — the cost-drag drawn onto the R curve,
recorded through a named **`net_r_equity`** tap/sink (sibling of the existing
`r_equity` tap; a sink is the only thing the registry can display, C8/C18/C22). No
new unit is invented: it is R, gross and net, **continuous with the existing
`net_expectancy_r`**. A bare **gross-R run with no cost model attached is valid**:
the cost layer is optional and additively composed-on (the zero-cost baseline is
the "default simple" floor).

**Cost is a COST MODEL — a composable C9 graph of cost nodes, in R, that
approximates (never claims) realism.** The realistic broker is *retired* (see
Forbids / the 2026-06-28 reframe): real friction — slippage (live
liquidity / order-size / volatility at fill), swaps (broker-set, time-varying),
even recorded feed spread (often a fake constant) — is **not historically
knowable**, so an authored-friction historical broker is "horseshoe-throwing". Its
replacement is a **cost model**: an ordinary downstream **C9 graph of cost nodes**
that *approximates* the cost side a broker would produce, explicitly as an
approximation. The cost nodes live in `aura-std` (the cost-graph composite-builder
in `aura-composites`), never in the domain-free `aura-engine` (C14/C16). They are
**not** "additive on the R stream" in isolation: a cost node **reads the state it
depends on** — the price stream, a realized-volatility tap, a C11-recorded
interest-rate source, and the executor's per-cycle R-record / trade events — and
emits a **cost-in-R** stream that is subtracted from gross R to yield net R. Cost
attaches at the structurally correct grain: **per-trade** factors (commission, a
flat cost-per-trade) deduct from `realized_r` at close; **per-cycle-held** factors
(carry / funding / swap) accrue over the holding duration. The model **generalizes**
the existing scalar `round_trip_cost` / `net_expectancy_r` into a possibly
**state-dependent graph**: the scalar `round_trip_cost` is the degenerate
constant-per-trade special case, **subsumed** by the cost graph — the post-run
`summarize_r` fold no longer recomputes cost independently but folds the
cost-model's net-R stream into `net_expectancy_r` (one home for cost, no
double-count). Discipline: every cost factor is **either** a clearly-labelled
**stress-parameter** (e.g. a flat cost-per-trade is a breakeven-threshold probe)
**or** **data-grounded / falsifiable** (e.g. realized-volatility → slippage;
recorded interest-rate data via C11 → funding / swap). **Default simple;
complexity is earned per grounded factor.** Stacking unfalsifiable guesses
(over-modelling) is the anti-pattern.

**The research loop is pure feed-forward — compounding is removed.** Flat-1R-style
R accounting needs no equity, and with the Sizer gone there is **no equity → size
edge at all** in research: the loop is **feed-forward, maximally parallel and
deterministic (C1)**, the cost model a feed-forward subtraction on the R stream.
**Compounding is removed from research**: it is a **post-strategy money-management
transform** — a pure function of the per-trade **net-R sequence** and a
bet-fraction *f*, multiplicative and path / order-dependent, the **sole** source of
feedback — so compounding, Kelly-*f*, and drawdown-under-compounding are derived
**post-hoc, analytically, at the deploy / account layer** from the net-R
distribution. Consequently the `z⁻¹` fill-edge register **and** the
flat-1R-vs-compounding structural axis are **gone from the research loop** (with no
in-loop feedback there is nothing for a register to cut, so the C23-reordering
hazard the old text invoked to make the register mandatory no longer exists — this
is strictly C9 / C23-cleaner).

**Conviction-based risk allocation survives — as an R-aggregation axis, not a
Sizer.** Scaling risk by bias strength is **signal-side and R-denominated**.
Because per-trade R is **size-invariant**, conviction cannot be expressed by
scaling position size (that is invisible to R); it is expressed by **weighting the
per-trade R-contribution** in the R-equity: **flat** (sum of `realized_r`, sign
only) vs **conviction-weighted** (sum of `|bias| · realized_r`, sign + magnitude).
This is a **feed-forward, additive, order-independent research axis** (flat vs
conviction-weighted R-aggregation), distinct from the removed money-Sizer; it is
tested via the existing `conviction_at_entry` field and `conviction_terciles_r`
metric, and may sit in-graph or as a post-hoc fold.

**Money / real broker / cTrader Open API = a separate, later live / deploy-edge
concern — the only `belastbare` (reliable) ground truth, measured never modelled.**
Reliable friction statistics require **forward-trading against a real broker**
(e.g. cTrader Open API), and are non-stationary even then. This fits C11
(record-then-replay: real fills are recorded live, then replayable) and the
frozen-deploy invariant (C13: deploy = frozen bot + broker connection);
reconciliation with the real account is an **external I/O adapter** at the
recording / deploy edge, not an in-graph node. **This is the only place account
money appears.** (Currency-denominated *reference geometry* — pip value,
stop-distance-in-currency from the C15 `instrument_geometry` sidecar — is still
read at the **ingestion** edge to normalize a currency / pip cost factor into R;
notional size cancels in `cost_in_R = cost_in_currency / (size · stop_dist)`, so
the cost model is R-pure without ever holding *equity*. It is equity / account
money, not reference geometry, that lives only at the deploy edge.) The
broker-independent **position-event table** (`event_ts, action[buy/sell/close],
position_id, instrument_id, volume`) is the **deploy / reconciliation** record at
this edge (real volume), not a research artifact.

**Honesty principle.** The net-R curve under the cost model is a **research /
ranking tool and a hypothesis**; the **forward / live run against a real broker is
the ground truth**. The cost model *approximates*; it **never claims realism**.
`SimBroker` (the pip-equity, unsized-exposure node) is the **pre-reframe pip
ancestor** — with the net-R cost model it is **redundant as a quality measure** (R
supersedes pips). It is retained as a **legacy / simple optional pip yardstick**
(still wired in the `r-sma` harness for an honest dual readout), **not part of
the new model and not to be expanded**.

**Forbids.** Putting **sizing or the stop in the strategy** (bias is unsized; the
stop-rule owns the stop, R is the unit); treating an **equity curve** (R or
currency) as the strategy's direct output; **putting a Sizer / currency size /
`volume` into the research loop** (size is a deploy concept; research is in R);
leaving a **dangling `size` input port** on the research executor (C8 wiring
totality forbids it — drop the port or drive it with a constant unit); **any
equity → size / equity → anything feedback in research** (the research loop is pure
feed-forward; compounding is a post-hoc money-management transform, not an in-loop
edge); modelling an **authored-friction "realistic broker" over historical data**
(real friction is not historically knowable — use the approximating cost model, and
treat the real broker as the live-edge ground truth only); **claiming the cost
model is realism** (it is an explicit approximation); **stacking unfalsifiable cost
guesses** (each cost factor is a labelled stress-parameter *or* data-grounded —
over-modelling is the anti-pattern); **computing cost in two homes** (the cost
graph owns cost; the post-run fold subsumes the old scalar `round_trip_cost`, never
double-counts it); expressing **conviction by scaling position size**
(size-invisible to R; conviction is an R-aggregation weight); making the
**position-event table the strategy's direct DAG output** (it is derived, not
emitted per `eval` — a decision instant may need >1 event, which C8 forbids) or a
**research** measure of signal quality (it is a deploy / reconciliation artifact);
**measuring signal quality in currency / account money** in the research loop at all
(account money lives only at the live deploy edge; reference geometry at ingestion
is not account money); baking a broker into the strategy or an **in-graph broker
subsystem** (the in-graph realistic broker is retired; the only broker is the
live-edge I/O adapter, C11 / C13); a signed-volume direction trick in the event
table (use `action`); storing `open_ts` (derive it from the opening event).

**Why.** A strategy's edge is a *procedure*, not a currency outcome ("focus on the
procedure, not the money"): the right primary question is *"how much R out per 1R
risked?"*, and R — defined by the stop — is the only account- and
instrument-agnostic, risk-normalized unit (pips are not). Separating **direction
(bias) from sizing from fill** is the decomposition every mature system converges
on (LEAN's Alpha → Portfolio-Construction → Execution is a near isomorphism;
backtrader, QSTrader, zipline all emit an unsized directional signal sized
downstream) — and aura pushes *sizing* and *fill* off the research loop for two
**distinct** reasons: **sizing** is off because per-trade R is **size-invariant**
(size carries no information in R — flat-1R is perfectly knowable, it just does not
matter), and **fill / friction** is off because real friction is **not
historically knowable** and therefore not honest over history. Keeping research
**pure feed-forward** leaves the signal-quality layer parallel and deterministic
(C1); the **only** real feedback (equity → bet-fraction) is **compounding**, a
closed-form, path-dependent transform of the net-R sequence, and therefore belongs
**after** the strategy, at the deploy / account layer, not as an in-loop register.
The **cost model as a C9 graph** keeps cost within the one Node / graph abstraction
(C9) and generalizes the scalar `net_expectancy_r` continuously, while the
**gross-R / net-R** split states the cost-drag honestly without inventing a unit.
Refusing the historical realistic broker is an **honesty** stance: the only
`belastbare` friction is **measured forward** against a real broker (cTrader Open
API) — the live deploy edge, the sole place account money and ground truth appear.
The DAG holds exactly one state at t and a node emits ≤1 record per `eval` (C8), so
the faithful per-cycle output is the **bias** (one value); position *events* are a
derived, deploy-side consequence. This supersedes the **realistic-broker /
currency / compounding / Stage-1-vs-Stage-2** framing of the #117 reframe (see the
2026-06-28 reframe note), which itself superseded the **exposure** framing of
cycle-0007 and the still-earlier "strategy's output is the position-event table"
framing.

**Reframe (2026-06-28, #116 — realistic broker retired; cost-model graph in R; money to the live edge).**
This is the live contract above. Ratified in an in-context design discussion
(reference issue #116). It **preserves** the durable spine — unsized bias stream
(sign = direction, magnitude = conviction), signal quality in R, the stop defining
R, and the decoupling of direction from sizing from fill — and the shipped Stage-1
realizations (the `Bias` node, `FixedStop` / `vol_stop`, `PositionManagement`,
`summarize_r` / `RMetrics` / `sqn_normalized`, SQN as ranking objective). The
**RiskExecutor composite survives in shape** (bias + price → stop-rule →
position-management) but with its **Sizer interior removed** and its `risk_budget`
argument dropped / vestigial (it sized the now-removed Sizer); the Veto remains an
optional documented seam. The contract **supersedes** the following, which were
**design intent, largely unbuilt** (#116 — the realistic broker and the whole
Stage-2 currency layer were never implemented; the Stage-1 R chain was) and are
retired:
- the **"realistic broker"** concept — an authored-friction historical broker —
  rejected as "horseshoe-throwing" (real friction is not historically knowable),
  replaced by the **cost model**: a composable C9 graph of cost nodes (in
  `aura-std` / `aura-composites`), approximating not claiming realism,
  generalizing / subsuming `round_trip_cost` into `net_expectancy_r`;
- the **"Currency P&L is Stage 2"** paragraph in full, the **Stage-1-vs-Stage-2
  hard sequencing gate**, and **currency / fixed-fractional / compounding** in
  research — compounding is now a post-hoc money-management transform of the
  net-R sequence at the deploy / account layer;
- the **`z⁻¹` register on the fill edge** and the **flat-1R-vs-compounding
  structural axis** as research mechanism — there is no equity → size edge in
  research, so no register and no such axis in the loop;
- the **Sizer in research** and currency **size / `volume`** — size is a deploy
  concept; the research executor is stop + position-management in R;
  `PositionManagement`'s `size` port is dropped or constant-driven (no dangling
  port, C8), its `size` field and the event table's `volume` are vestigial in
  research;
- the **"a broker is an ordinary in-graph node / no special external broker
  subsystem"** forbid, **for the live edge only**: in-graph brokers are retired
  outright, and the live broker is now an explicit **I/O adapter** at the C11
  recording / C13 deploy edge — not an in-graph node and not part of the research
  graph (the no-in-graph-broker-subsystem prohibition still holds inside the
  graph);
- the **position-event table as the realistic-broker input** and its
  first-difference-of-the-book (`deal = target − book − in_flight`) execution
  framing — the table (schema 0063 #114, derive 0068 #115) **survives** as the
  **deploy / reconciliation** artifact (real volume), not a research artifact and
  not "fed to a broker" in research.
Money, a real broker, and cTrader Open API are a **separate, later live /
deploy-edge** concern (C11 record-then-replay; C13 frozen-deploy invariant) — the
only `belastbare` ground truth, measured, never modelled. The honesty principle is
explicit: the net-R curve is a research / ranking hypothesis; the forward / live
run is ground truth. `SimBroker` is downgraded to a legacy / optional pip
yardstick, not to be expanded. (Terminology note: with Stage 2 gone, the
**"Stage-1"** label below is no longer one half of a two-stage gate — it survives
only as a historical cycle name, like the `exposure` → `bias` on-disk alias,
denoting the shipped feed-forward R chain; the identifier family that carried it
was renamed to the r-family — `r-sma` / `r-breakout` / `r-meanrev` — in cycle
0100, #174.)

**Realization (cycle 0081 — cost-model graph, cycle 1, #148).** The first concrete
cost node + the net-R seam shipped. `ConstantCost` (`aura-std`) is an ordinary
downstream node (C9) emitting a 3-field cost-in-R record `{cost_in_r, cum_cost_in_r,
open_cost_in_r}` isomorphic to `PositionManagement`'s R-triple; R-pure
(`cost_per_trade / |entry − stop|`, notional cancels, no equity held). The scalar
`round_trip_cost` argument of `summarize_r` is **retired**: `summarize_r` folds a
co-temporal cost stream (positional 1:1 join — `cost[i]` is `record[i]`'s cycle) into
`net_expectancy_r`, one home for cost / no double-count, byte-identical to the old
cost = 0 baseline on an empty stream. The headline sink is **`net_r_equity`** =
`LinComb(4)[cum_realized_r, unrealized_r, −cum_cost_in_r, −open_cost_in_r]` → Recorder
(C8/C18), a sibling of `r_equity`, emitted only when a cost is authored. Wired on the
**run path** via `--cost-per-trade` (`r_sma_graph`); sweep / walk-forward / mc pass
`None` (cost on the reduce-mode sweep path and cost in OOS pooling deferred — the
positional join holds only while one cost node fires in lockstep with PM).
[Superseded 2026-07-11 (#234): the `--cost-*` run-path flags are gone (#221 removed
that surface); cost is authored as the campaign document's `cost` block and reaches
every family/campaign member — see the cycle-net-r realization below.] Deferred to
later milestone cycles: the general `CostNode` trait + multi-node cost-graph
composite-builder, data-grounded factors (realized-vol → slippage, recorded-rate →
swap), per-cycle-held accrual (carry / funding), and the conviction-weighting
R-aggregation axis. Decision log: #148.

**Realization (cycle 0082 — cost-graph composition, cycle 2, #148).** The cost graph
**composes**: a second, *state-dependent* cost node plus an aggregator prove that two
cost nodes sum into one net-R curve with `summarize_r` and the `net_r_equity` tap
structurally unchanged. `VolSlippageCost` (`aura-std`) charges `slip_vol_mult · vol /
|entry − stop|` in R, reading an **independent short-horizon realized-range** vol
(`RollingMax − RollingMin`, window distinct from the stop's own vol — scaling slippage
by the stop's vol would collapse cost-in-R to a constant, indistinguishable from
`ConstantCost`). `CostSum` (`aura-std`) is the cost-graph **output node**: it sums `N`
cost nodes' 3-field cost-in-R records **per-field** into one aggregate (`n = 1` is the
identity), so the seam consumes a single cost stream regardless of node count — one
home for cost, the positional join unchanged. **Co-temporality contract (load-bearing,
generalizes to all future factors):** since `summarize_r` positionally joins `cost[i]
↔ record[i]`, a cost node is gated **only by the PM trade-geometry**; any not-yet-warm
state input (the vol proxy warms later than PM) contributes **0 cost** that cycle
rather than withholding — the node still emits its row, so the cost stream stays
co-temporal 1:1 with the PM record. This makes co-temporality structural and
warm-up-independent, preserves the C18 golden, and is honest (no slippage estimate yet
→ no charge). `ConstantCost` satisfies it trivially; only state-dependent nodes need
the missing-factor → 0 rule. Wired on the **run path** via `--slip-vol-mult`,
composable with `--cost-per-trade` (their costs sum); sweep / walk-forward / mc pass
`None`. The 3-field cost triple is now restated by-convention across the two producers
+ `CostSum` (a compiler-unlinked lockstep) — to be unified by the still-deferred
general `CostNode` trait (now justified by two concrete nodes). Decision log: #148.
[Superseded 2026-07-11 (#234): the `--slip-vol-mult`/`--cost-per-trade` flags are gone;
authoring moved to the campaign `cost` block — see the cycle-net-r realization below.]

**Realization (cycle 0083 — CostNode trait + shared cost-record contract, cycle 3,
#148).** The deferred unifier ships. A new `aura-std/src/cost.rs` owns the cost-model
node abstraction: the 3-field cost triple is now **one source of truth**
(`COST_FIELD_NAMES` / `COST_WIDTH`, mirroring `position_management::{FIELD_NAMES,
WIDTH}`), read by both producers + `CostSum` + the CLI wiring — the cycle-0082
by-convention lockstep is **structurally gone** (four restatements collapsed to one).
The `CostNode` **factor trait** carries a cost node's only per-node difference — the
price-unit **cost numerator** (`cost_numerator(&mut self, &Ctx) -> f64`), plus
`extra_inputs` (default none) and `label`; everything else is the generic
`CostRunner<F: CostNode>` **adapter**, which holds the shared `cum`/`out` state and
implements `Node`, writing the co-temporality skeleton (geometry-only gating,
`numerator / latched` R-normalization, the closed/open charge, the running `cum`, the
3-field emit) **once**. `ConstantCost` and `VolSlippageCost` are now thin factors whose
`new()` returns `CostRunner<Self>`. Honours C9 (a `CostRunner<F>` is a plain downstream
`Node`, no runtime sub-object) and C23 (`name()` dropped as dead surface — `label()`
remains the non-load-bearing symbol). **Behaviour-preserving**: the builders emit
unchanged schemas, so the wiring / `net_r_equity` seam / `summarize_r` are untouched and
the `numerator / latched` token form is byte-identical; the existing suite passes
verbatim and two new CLI characterization goldens pin the exact flat/composed
`net_expectancy_r` (the prior tests only asserted `net < gross`). Decision log: #148.

**Realization (cycle 0084 — cost-graph composite-builder, cycle 4, #148).** Decision E
ships. A new `cost_graph(Vec<PrimitiveBuilder>) -> Composite` in `aura-composites` (the
C16 layer that couples the engine builder + `aura-std` nodes) is the cost-model graph's
**authoring primitive**: it fans the 4 PM-geometry inputs to `N` cost nodes, surfaces
each node's extra inputs (discovered via `schema().inputs[GEOMETRY_WIDTH..]`,
`GEOMETRY_WIDTH` now re-exported from `aura-std`) as `cost[k].<port>` composite roles,
sums them through `CostSum`, and exposes the 3-field aggregate. The CLI's manual
slot-indexed cost-wiring + the hardcoded `MAX_RUN_COST_NODES = 2` cap are deleted — the
composite handles arbitrary arity. **Behaviour-preserving** (C11): the composite inlines
at bootstrap to the same flat fan-in, so the cycle-0083 `net_expectancy_r` goldens are
byte-identical (four `aura-composites` unit tests pin the exposed role-set + output
triple, incl. arbitrary-arity per-node namespacing). Honours C9 (ordinary downstream
nodes), C16 (wiring stays out of `aura-engine`), C23 (role/port names are
non-load-bearing). **Carried debt (#152, for the deferred sweep-cost cycle):** the
`cost[k].<port>` index-namespacing is restated across `CostSum` / `cost_graph` / the CLI
(a build-validated lockstep, not the silent positional kind 0083 collapsed), and
`cost_graph` `.leak()`s runtime port names per build — fine for one-shot run-path
construction, but to be interned (the `COL_PORTS` production pattern, not the test-only
`.leak()`) before cost reaches the per-member sweep path. Decision log: #148.
[Discharged 2026-07-11 (#152/#234): `cost_port`/`intern_port` in `aura-std/src/cost.rs`
are the process-global interned single source; both `cost_graph` `.leak()`s are gone.]

**Realization (cycle 0085 — per-cycle-held accrual, cycle 5, #148).** C10's
"per-trade factors deduct at close; **per-cycle-held factors accrue over the hold**"
clause is first realized. A cost factor now declares *when* it charges via
`ChargeMode { AtClose, PerHeldCycle }` (a defaulted `CostNode::charge_mode()`, default
`AtClose`), read by the **one shared `CostRunner`** — not a second runner type (a
commission is intrinsically at-close, a carry intrinsically per-held-cycle; the timing
belongs to the factor, preserving the cycle-0083 "skeleton written once" win). The
`PerHeldCycle` arm accrues `per` into a per-position `acc` every held cycle, dumps the
accrued total into `cum` at close (resetting `acc`), and marks the open position via a
**growing `open_cost_in_r`**. The first accrual node, **`CarryCost`** (`aura-std`,
a `ConstantCost` twin differing only in `charge_mode()`), is a labelled stress
parameter — the flat base of the accrual family; a run-path `--carry-per-cycle` flag
pushes it into the existing `cost_graph`/`CostSum` aggregation (no new wiring; a
per-trade and a per-held-cycle node compose, the costs summing per-field). **Approach B
(honest bleed), achieved without a `summarize_r` fold change:** the headline
`net_r_equity` curve bleeds continuously over the hold because the bleed lives in
`open_cost_in_r`, which the `net_r_equity` tap already subtracts — so `summarize_r` and
the CLI `net_eq` wiring are **untouched**, and the cycle-0083/0084 `net_expectancy_r`
goldens stay byte-identical (the `AtClose` arm is the pre-cycle-5 eval tokens verbatim).
The 3-field cost record's semantics generalize cleanly: `cost_in_r` = cost realized this
cycle (into `cum`); `open_cost_in_r` = the open position's cost marked-to-market
as-of-now (would-be-close for `AtClose`, accrued-so-far for `PerHeldCycle`) — singly
counted, no `cum`/`open` double-count (the two are mutually exclusive per cycle). Honours
C9 (a `CostRunner<CarryCost>` is an ordinary downstream `Node`), C11 (byte-identity), C16
(factor in `aura-std`, `aura-engine` domain-free), C23 (`label()` carries the rate). The
B-vs-A discriminator (a growing intra-hold `open_cost_in_r`, invisible to the scalar
`net_expectancy_r`) is pinned by unit B-proofs + a `net_r_equity`-bleeds-over-the-hold
integration test. **Deferred (each its own #148 cycle):** a notional-based carry
(`price × rate`, reads the price tap), the calendar-aware **overnight swap** proper
(rollover-boundary timing, 3× Wednesday, long/short asymmetry — deploy-edge realism), and
sweep-path cost. Decision log: #148.

**Realization (cycle net-r — cost reaches the family/campaign path, #234/#152,
2026-07-11).** The deferred sweep-path cost ships, delivered where C24 put experiment
intent: the campaign document gains an additive `cost: Vec<CostSpec>` block — a closed,
externally tagged vocabulary over the three shipped nodes (`constant` / `vol_slippage`
/ `carry`, field names = the builders' own `ParamSpec` names), mirroring the `risk`
block (serde `default` + skip-if-empty: cost-less docs hash byte-identically, C18).
Net is the **default**: an absent block is the explicit zero-cost model and
`summarize_r`'s net family equals gross under it — every result is net, no second
"gross-labelled" result kind. `cost_nodes_for` (beside `stop_rule_for_regime`) is the
one doc→builder binding, every component fully bound (the wrapped param space stays
cost-invariant); `wrap_r` carries an optional cost leg (the #221-deleted wiring
rebuilt: cost_graph off the executor's four geometry outputs, the vol proxy back in
production, a gated cost recorder in reduce mode as the `summarize_r` join input, the
`LinComb(4)` `net_r_equity` curve in trace mode). Member manifests stamp the
components; both re-run sides re-derive them (reproduce via `cost_specs_from_params` —
the #233 stop pattern — and the persist re-run binds the same model, so the C1 drift
alarm compares like with like; costed families reproduce bit-identically, pinned incl.
`Carry`). `TapChannel::Net` routes `net_r_equity` to persisted curves; a cost-less doc
requesting it keeps a remedy-naming skip notice. The `--cost-*` run-path flags do not
return; the verb sugar passes no cost (docs carry it) — the same lean-flag call as the
C26 bindings block. #152's interning ships with it (`cost_port`/`intern_port`, both
`cost_graph` `.leak()`s gone). Decision log: #234.

**Realization (cost-flag harness scoping, #153).** Cost flags are defined only
against an R-evaluator harness (the gross-R → net-R chain). On a non-R harness
(`--harness sma`/`macd`, which produce no R) a cost flag is a **usage error
(exit 2)**, not a silent no-op — refuse-don't-guess. Negative cost rates are
likewise rejected (exit 2) with a named diagnostic that identifies the offending
flag. CLI ergonomics only; the cost-model graph and the R math are untouched.
[HISTORY — the built-in `--harness` selector (its `sma`/`macd` non-R examples)
was retired with the demos → blueprint-data (#159, cuts 1b-4); the cost-flag
scoping rule survives on the `aura <verb> <blueprint.json>` r-sma run path over
examples/r_*.json.]

**Reframe (2026-06-23, #117 — exposure → bias, R as the signal-quality unit).**
[HISTORY — its R spine survives into the 2026-06-28 contract; its Stage-2 currency /
realistic-broker / register / flat-1R-vs-compounding portions are SUPERSEDED by that
reframe.] The contract was reframed from **exposure** (a signed fractional
position) to an **unsized bias** plus **R** as the signal-quality unit. The
realization notes below describe the **pre-reframe code** (`Exposure`, `SimBroker`,
pip-equity), retained as history and as the **ancestor** of the current chain:
`Exposure { scale }` is the ancestor of the unsized `bias` node, and `SimBroker`'s
pip integral is the ancestor of the R-evaluator (which additionally requires a
stop, since R is stop-defined). The `exposure → bias` rename, the RiskExecutor /
Sizer / Veto nodes, and the R-evaluator **landed in cycle 0065**; the
position-event schema (0063, #114) survives as the audit layer. Industry grounding
for this reframe: LEAN / nautilus_trader / backtrader / QSTrader / vectorbt /
zipline (see #117 decision log).

**Realization (cycle 0007).** [HISTORY — pre-reframe; `SimBroker` is now legacy per
the 2026-06-28 reframe.] The signal-quality half was realized at the substrate as
two `aura-std` nodes on the unchanged engine (the engine stays domain-free — it
routes only `f64` records). The **exposure stream** was realized as `Exposure {
scale }`: `clamp(signal / scale, -1, +1)`, one `f64` per fired cycle. The
**sim-optimal broker** was realized as `SimBroker { pip_size }`: a two-input node
(exposure, price) accumulating `prev_exposure · (price − prev_price) / pip_size`
and emitting cumulative pip equity — the exposure held *into* a cycle (decided at
t-1) earns that cycle's return (causal, C2); `pip_size` is held reference metadata
(C7/C15). An end-to-end harness (SMA-cross → `Exposure` → `SimBroker` → recording
sink) produced a recorded pip-equity curve, bit-identical across runs (C1).

**Realization (per-instrument pip channel, 2026-06, #22).** [HISTORY — pertains to
the legacy `SimBroker` pip channel.] `SimBroker`'s `pip_size` is sourced **per
instrument** from the recorded geometry sidecar (`instrument_geometry`, over
data-server's `symbol_meta`), at the ingestion / source edge (never `Aura.toml`,
never `Ctx`); the engine stays domain-free. (The original cycle-0022 form was a
Rust-authored vetted floor `InstrumentSpec { pip_size }` + `instrument_spec(symbol)`;
cycle 0074 removed that floor — see the C15 note — once the sidecar geometry made it
redundant for the real path. Refuse-don't-guess on absent geometry.) The honesty
rule is **refuse, don't guess**: a real-data run for a symbol with no vetted spec
is a usage error (`exit 2`). Threaded through the CLI `aura run --real` path; the
manifest broker label records the looked-up pip.

**Realization (position-event schema, cycle 0063, #114).** [Survives as the
**deploy / reconciliation** schema per the 2026-06-28 reframe — no longer a
broker-input research artifact.] A closed `PositionAction { Buy, Sell, Close }`
enum + the `PositionEvent` row (`event_ts`, `action`, `position_id`,
`instrument_id`, unsigned `volume`; no `open_ts`; direction *is* the action) live
beside `RunMetrics` as a post-run value type (not a per-`eval` node — C8) — both in
the `aura-analysis` crate since cycle 0079 (#136); originally `aura-engine`, see the
C16 cycle-0079 note. `action` serde-encodes as a bare `i64` (Buy=0, Sell=1,
Close=2), the C7 scalar column form, with an out-of-range code rejected on read.
The table stays broker-independent.

**Realization (cycle 0065 — Stage-1 R signal quality, #119/#126/#127/#128/#129).**
[The R spine here is the live model; the *Stage-2 deferral* clause at its end is
SUPERSEDED by the 2026-06-28 reframe — there is no Stage-2 currency / compounding
layer; cost is now the cost-model graph and money lives only at the live deploy
edge. "Stage-1" reads as a historical identifier, not a gate half.] `Exposure →
Bias` renamed the unsized strategy output (node + output field); the persisted
`exposure_sign_flips` metric key (serde alias), the `SimBroker` `exposure` input
slot, and the on-disk `exposure` **tap** label retain the old name. The
strategy-output **param namespace** (the `Bias` instance, its `bias.scale` knob,
the `bias_scale` manifest param) was completed in #134. A **stop-rule** defines 1R:
`FixedStop` (a triggered-constant primitive) and a `vol_stop(length, k)`
**composition** `k·√EMA(Δ²)` (a composition of `Mul` / `Sqrt` primitives).
**`PositionManagement`** (`aura-std`) is the stateful heart: it latches the
entry-cycle stop distance as the immutable R-denominator, marks against the
one-cycle-lagged fill (no look-ahead, C2), and emits a **dense 14-column per-cycle
R-record** (one row per eval, C8; the trade ledger is the `closed_this_cycle`
subset, the R-equity is `cum_realized_r + unrealized_r`). The **`Sizer`** (`size =
risk_budget / stop_distance`, flat-1R) was the feed-forward sizing seam, and **R is
size-invariant** — scaling `risk_budget` leaves every `realized_r` unchanged
(pinned by a RED test); per the 2026-06-28 reframe the Sizer and `size` / `volume`
are removed from research (size is a deploy concept). **`summarize_r`** is a
post-run fold (sibling of `summarize`, **not** an in-graph node) → `RMetrics` (E[R],
SQN, win-rate, profit-factor, max-R-drawdown, conviction terciles, net-of-cost);
per the 2026-06-28 reframe it folds the cost-model's net-R rather than recomputing
a scalar cost. The **RiskExecutor** ships as a public `aura-composites`
composite-builder (`risk_executor(StopRule, risk_budget)`) with a
`StopRule{Fixed,Vol}` **structural axis** (C20); per the 2026-06-28 reframe its
Sizer interior and `risk_budget` arg are dropped / vestigial, the **Veto** stays a
documented seam, not a runtime node. The layer is operable from the CLI: `aura run
--harness <sma|macd|r-sma>` — a compile-time selector over Rust-authored
harnesses (C9/C17) — folds `summarize_r` into `RunMetrics.r`, the `r-sma`
harness fanning one bias into both `SimBroker` (legacy pip) and the RiskExecutor
(R); an `r_equity` tap charts the by-trade R-equity. Composites live in the
dedicated `aura-composites` crate, so `aura-engine`'s runtime dependency stays
`aura-core`-only and `aura-std` is an `aura-engine` `[dev-dependencies]` (the graph
stays acyclic).
[HISTORY — the built-in `--harness` selector was retired with the demos →
blueprint-data (#159, cuts 1b-4); `run` is now blueprint-driven — `aura run
<blueprint.json>` over examples/r_*.json.]

**Realization (2026-07-06 — the risk regime as a structural campaign axis, #210).**
The `StopRule{Fixed,Vol}` structural axis is realized at the campaign-document
level as `CampaignDoc.risk: [RiskRegime]` (a serializable, content-addressable
mirror of the runtime enum — `aura-research`, variants `Vol{length,k}` and
`VolTf{period_minutes,length,k}` (#262), the fixed-stop rule additive when
needed). It is a **kept-separate** matrix axis, a
peer of instruments and windows: the executor keys the nominee map by
`(strategy, window, regime)`, so generalize aggregates across instruments
*within* a regime, never across regimes. Regimes are therefore **compared** at
presentation, never argmax-**selected** across — a cross-regime E[R] argmax would
compare R-multiples in different R units (the stop defines 1R), so the legacy
verbs' `--stop-length`/`--stop-k` joint stop grid is retired as a campaign
methodology (finding the best regime = the same walk-forward / worst-case-R
validation, run once per regime, and picking the most robust — a comparison, not
a search). Each member manifest stamps its resolved stop (default included),
closing the C18 gap; absent/empty `risk` = one implicit default regime,
absent-serializing for content-id parity. Two default *representations*
coexist by design (#217): a dissolved sweep binds no regime at all
(`risk: []`), late-resolved per member by `stop_rule_for_regime` at run
time, while walkforward/mc/generalize — whose `--stop-length`/`--stop-k`
became optional — bind the default regime *eagerly* into the campaign
document (`risk: [Vol{length:3,k:2.0}]`). Same R behaviour either way, but
deliberately different document content ids: a stop-less verb invocation's
document equals its explicit `--stop-length 3 --stop-k 2.0` spelling, not
a stop-less sweep's document. Deferred (documented): regime-aware
**trace** persistence — the trace re-run and cell-key dir naming still assume the
default stop, since `CellRealization` carries no regime (`#212`); the core
run/stamp/generalize path is unaffected.

**Realization (cycle 0066).** SQN is the operational single-number objective for
ranking an r-sma sweep family by signal quality — C12 **axis-2 (argmax-metric)**
over the C18 family store. `metric_cmp` (`aura-registry`) learns the
higher-is-better R metrics `sqn`, `expectancy_r`, `net_expectancy_r`; a member
with no `r` block sorts last (`NEG_INFINITY`). `aura sweep --strategy r-sma`
produces the rankable R family, each member folding `summarize_r` into
`RunMetrics.r`. The default grid varies **only the signal** (`fast` / `slow` SMA
lengths), holding the stop and sizing fixed: `risk_budget` is R-invariant and
`bias.scale` is sign-only under flat-1R, and — load-bearing — the **stop defines
1R**, so varying it would change what R *means* per member and break cross-member
SQN comparability. Each swept member's manifest records the fixed R-defining params
beside the floated knobs (reproducible from its own manifest, C18).
[HISTORY — the built-in `--strategy` sweep surface was retired with the demos →
blueprint-data (#159, cuts 1b-4); the rankable R sweep now runs as `aura sweep
<blueprint.json> --axis …` over r_sma_open.json (an example then; relocated to
`crates/aura-cli/tests/fixtures/` by #248).]

**Realization (cycle 0067, #130 + #135).** **#130 (SQN100):** `RMetrics` gains
`sqn_normalized = (mean_R/stdev_R)·√(min(n, 100))` — the n-normalized "SQN score"
(`SQN_CAP = 100`), turnover-robust where raw `sqn` rewards trade count. It is an
**opt-in** rank key (`Metric::SqnNormalized`); raw `sqn` and the default ranker
stay byte-unchanged, and the field carries `#[serde(default)]` (C18). Below the cap
(`n ≤ 100`) it equals raw `sqn` exactly. **#135 (r-sma `--trace`):**
`r_sma_sweep_family` persists each member's equity / exposure / r_equity under
`runs/traces/<n>/<member_key>/` via the same `persist_traces_r` the single run uses;
per-member `--trace` is symmetric across all three sweep strategies.
[HISTORY — the built-in `--strategy` sweep triple (sma / momentum / r-sma) was
retired with the demos → blueprint-data (#159, cuts 1b-4). The per-member
`--trace` symmetry was NOT carried to the `aura sweep <blueprint.json>` path — it
was silently dropped at #159/#220 (`run_blueprint_sweep` never wired `persist`;
`let _ = persist`), and #168 makes the surface honest: `sweep`/`walkforward` (like
the pre-existing `run`/`mc`) now refuse `--trace` outright. See the CLI-`--trace`
retirement amendment below.]

**Realization (cycle 0068, #115 — position-event derive).** [The derivation
survives as the **deploy / reconciliation** layer per the 2026-06-28 reframe — its
"realistic brokers consuming it" goal is retired; money is the live-edge concern.]
`derive_position_events(record, instrument_id) -> Vec<PositionEvent>` (in
`aura-analysis` since cycle 0079, #136; originally `aura-engine`, beside
`summarize_r`) is the **first difference of the executed book**: a pure post-run
reduction over the `PositionManagement` dense record (read positionally as
type-erased `Scalar`s, C7 SoA — no in-graph node, so the hot path stays
domain-free, C14), emitting a `Buy` / `Sell` at each open and a `Close` at each
exit, a reversal (or stop-then-same-cycle reopen) emitting **Close then the
opposite open at one `event_ts`** (close first — the C8 ">1 event per instant" case
that forces a *derived* table, not a per-`eval` output). The close sizes the
**actual book** (the closed position's stored volume), never an exposure delta.
`instrument_id` is a caller-supplied scalar (`aura-analysis` depends only on
`aura-core`). A position open at window end emits its open with **no synthetic
`Close`** (the table records actual executed events; `summarize_r`'s force-close is
for the R metric only). The `r_col` ⟷ PM-record lockstep is guard-pinned for
`direction` too.

### C11 — Generalized sources; record-then-replay determinism boundary
**Guarantee.** A source is anything that produces timestamped scalar streams —
market data (`data-server`) and non-financial sources (e.g. a news-agent node
emitting a bias) are treated identically. Anything nondeterministic, external,
or slow (LLM/news/web) is materialized into a recorded, timestamped stream
*before* it enters the engine; backtest replays the recording, live computes
fresh in real time and records it for future backtests. A bias enters as a value
held until the next event (firing policy A).
**Forbids.** Any live external call *inside* a backtest replay.
**Why.** It is the only model compatible with reproducible backtests — LLM calls
are nondeterministic and far too slow per-cycle. Per `~/.claude/CLAUDE.md`,
external LLM (IONOS) calls happen only at the recording/live-source edge, with
explicit per-session consent, never inside a sim.

### 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). Raw data is shared read-only across sims via
`Arc<[T]>` (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.
**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.
**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.
**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).
**Amendment (2026-07-12, #246).** A bound blueprint param is the param's
**default**: 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. "Open" means *must be bound by an axis*; "bound" means *default,
overridable by an axis*. `run`/`mc` still require every param resolved (a truly
open param still refuses). Identity is untouched: `content_id_of` and
`topology_hash` read the authored document, never a re-opened probe, and each
member manifest records its per-cell bindings as before. The restriction this
amends — axes bind only open knobs — was an implementation consequence of
`bind()` shrinking the param surface, not a recorded decision.

### C13 — Hot-reload is authoring-only; deploy is frozen
**Guarantee.** A node/strategy is authored as a native Rust `cdylib`,
hot-reloaded during the authoring loop (Rust-ABI; host and node built with the
same toolchain). The live/deploy bot is a statically-linked, versioned, frozen
artifact.
**Forbids.** Hot-swapping a running live bot; loading third-party / foreign-
toolchain plugins.
**Why.** Hot-reload makes the research loop fast; a live artifact must be frozen
and reproducible (audit trail: this bot = this commit). A sweep pays no
hot-reload tax — params are runtime data (C12), so the cdylib loads once.
**Realization (cycle 0102 — the load boundary; per-invocation reload).** The
authoring-loop half is realized: a project is an external cdylib crate loaded
per invocation through a two-tier `#[repr(C)]` descriptor (`AURA_PROJECT`,
`aura-core::project`) — a C-ABI stamp prefix (rustc version + aura-core
version, baked per consuming build) validated **before** any Rust-ABI field is
touched, then the vocabulary resolver + enumerable type-id list behind the
stamp gate. "Hot-reload" reads, in v1, as **per-invocation load of the
freshest build**: the author (Claude) runs `cargo build`, the next `aura`
invocation locates the artifact via `cargo metadata` (debug default,
`--release` opt-in) and loads it **load-and-hold** (leaked, never unloaded).
Scope boundary: load-and-hold is trivially sound only because the CLI is a
one-shot process — a future long-running host (the open local-server thread,
C22) must re-solve reload (host restart or subprocess isolation), never
in-process unload. Mismatch of either stamp refuses (exit 1) naming both
sides; the project vocabulary is charter-checked at load (`::`-namespaced ids,
no duplicates against std, list↔resolver cross-check) — the invariant-9
data-plane discipline of the C24 enforcement-shift note, now enforced at the
one seam.

### C14 — Headless core, two faces
**Guarantee.** The engine is a UI-agnostic library. Two faces sit on it: a
**programmatic/CLI** face (the primary surface for the LLM and automation —
author a node, run a sim/sweep, emit structured metrics) and a **visual** face
for human exploration. Visualization is only a downstream consumer node on the
streams.
**Forbids.** Any UI/pixel knowledge inside the engine.
**Why.** The LLM drives programmatically, the human visually; a headless core
serves both. The visual face is the **playground** (C22) — a **web frontend
served from disk-persisted traces** (revised 2026-06, issue #101: the engine
writes recorded traces to disk, a browser charts them; supersedes the earlier
egui-native / in-process-zero-copy-from-SoA direction). It is staged after the
runnable substrate but is core to aura's identity, not optional. The pivot keeps
this contract's core intact — and arguably tightens it: a browser reading a
serialized trace file is a stricter "no UI knowledge in the engine" than egui
reaching zero-copy into the live SoA columns.
**Realization (cycles 0098/0099, #175 — the CLI meets GNU/clig.dev conventions
via clap).** The programmatic/CLI face's argument surface moved from a hand-rolled
argv parser to a `clap` derive parser (admitted under the C16 per-case dependency
policy — research-side, a dev-loop/compile tax, never a frozen-artifact tax;
invariant 8 untouched, the change is confined to `aura-cli`, a leaf binary the
frozen deploy artifact cannot pick up). One declarative source now yields scoped
`aura <sub> --help`, `--version`/`-V`, a per-flag Options section, and GNU
`--flag=value` / `--` / long-option abbreviation. The **exit-code partition** is a
durable part of the automation contract, so a caller can branch on the failure
class without parsing stderr: **exit 0 = success**; **exit 2 = usage error** — a
command-line fault (clap parse errors + aura's post-parse argument-structure
validations, *including* the content of an argv-named blueprint file, which is
itself an argument); **exit 1 = runtime failure** — a well-formed command whose
needed environment / recorded state is missing, or bad piped stdin data. The four
dual-grammar subcommands (run/sweep/walkforward/mc) keep both grammars under one
token via an optional `[blueprint]` positional + a post-parse `is_file()`
dispatch; the execution layer is unchanged (arg-plumbing via thin `*_from`
adapters). Error-message casing is normalized to the clap house style —
every hand-rolled usage line reads `Usage: aura <verb> …` (#179, cycle 0101);
refusal diagnostics stay unprefixed (diagnostics are not usage lines). The
machine-first help surface (JSON/manifest help, stdin op-scripts) stays on the
#157/C21 track, not this cycle (settled as human/GNU convention compliance).
**Amendment (2026-07-13, #249 — two artifact classes, two redundancy budgets).**
The data layer the programmatic face emits is a public interface read raw (by
humans and LLMs), and its records split into two classes with opposite
redundancy budgets: **generated outcome records** (manifests, metrics, family
reports) have a single writer at run time — redundancy there cannot drift and
is deliberately spent on direct readability; **authored intent artifacts**
(blueprints, op-scripts, campaign documents) are author-maintained — every
redundancy is a drift site and stays out. Consequence shipped with #249: a run
manifest stamps the untouched bound defaults (`defaults`, one-directionally
widened beside `params`, which keeps its "what varied" reproduce semantics) so
a raw reader of a fully-bound run no longer sees a misleading `"params": []`;
the blueprint itself carries no such duplication.

### C15 — Resampling-as-node; sessions/calendars
**Guarantee.** A resampler is a node (finer stream → coarser bar stream),
clock-sensitive, emitting a completed bar only at the boundary (C2). Calendars
and instrument specs are metadata (non-scalar, beside the hot path); session
*context* is exposed as scalar streams via a `SessionNode` (`bars_since_open:
i64`, `in_session: bool`, `session_open_ts: timestamp`). "3rd 15m candle after
session open" is then a plain node checking `bars_since_open == 3`.
**Forbids.** Streaming the calendar; special-casing session logic outside the
stream model.
**Why.** Keeps the line consistent — everything a signal needs arrives as a
stream; reference data feeds source/session nodes from beside the hot path.
**Realization (instrument specs, 2026-06, #22 → #124).** The "instrument specs are
metadata" half of this contract is realized by the **recorded geometry sidecar**:
`instrument_geometry(server, symbol)`, over data-server's `symbol_meta`, returns
neutral broker-agnostic `InstrumentGeometry` (the raw provider JSON never enters this
repo) — non-scalar reference data held beside the hot path, keyed by symbol, feeding
the sim-optimal broker's pip divisor (C10). The real-path pip is sourced from
`InstrumentGeometry.pip_size`; refuse-don't-guess on absent geometry. **History:**
cycles 0022/0063 first carried a Rust-authored vetted floor (`InstrumentSpec` — a
single `pip_size`, later a six-field deploy-grade row `instrument_id`,
`contract_size`, `pip_value_per_lot`, `min_lot`, `lot_step`, `quote_currency`, plus
`tick_size`/`digits`), cross-checked against the sidecar geometry. **Cycle 0074
removed that floor**: with the sidecar geometry supplying the real-path pip, the
authored table was redundant, so `InstrumentSpec` / `instrument_spec` / the vetted
list were deleted. The speculative deploy-grade fields and the override/floor tiers
of the #124 hierarchy (tier 1 authored override, tier 3 authored floor) are
**deferred** until a consumer — the cost model's currency→R normalization (C10), or
the live deploy edge (real broker) — needs them, read from the sidecar geometry then. The `quote_currency` runtime-type transition is likewise
deferred to that consumer; #124 collapses to **recorded sidecar geometry → refuse**
in the meantime.

**Realization (SessionNode — `bars_since_open` only, by design; #154).** The
session-context half of this contract ships **one** scalar stream, not the three the
Guarantee lists: `Session` (`crates/aura-std/src/session.rs`) emits only
`bars_since_open: i64` (tz-aware, DST-correct, baked Frankfurt open). This is a deliberate
narrowing pinned in the node's own contract — *"there is no separate in-session bool gate,
`bars_since_open` alone is the contract"*: a downstream `EqConst(== N)` gate subsumes the
`in_session: bool` stream (pre-open instants give `<= 0`, which never match), and
`session_open_ts: timestamp` has no consumer. The two streams the Guarantee names remain
the original design intent, **deferred until a consumer needs them** (default-simple;
forward-queued as #154). The stream model is untouched — session context is still exposed
as scalar streams fed from beside the hot path.

### C16 — Engine / project separation; three-tier node reuse
**Guarantee.** aura is the reusable **engine**; each research project is a
separate external repo that depends on aura via cargo (the game-engine / game
split). Node reuse is cargo-native, in three tiers: **`aura-std`** (universal
blocks, ship with the engine) / **shared node crates** (cross-project-reusable,
their own repos, pulled as cargo git deps) / **project-local `nodes/`**
(experimental, project-specific). A reusable node is an `rlib` dependency; the
hot-reload unit stays the project-side `cdylib` that composes it (consistent
with C13). Concretely a project is a **Rust crate** — a cdylib library of node /
strategy / experiment blueprints — plus a static `Aura.toml` (project context,
paths only: data archive root, runs dir — cycle 0102). During
research the `aura` host loads and runs it (C13 hot-reload); for deploy the
chosen strategy + broker freeze into a standalone binary. **A project is
therefore always a Rust program built on the engine.** Beyond the node-reuse
tiers, the engine workspace also carries non-node crates — `aura-engine` (the
run loop), `aura-cli` (the `aura` binary), and **`aura-ingest`** (the
data-source ingestion edge, cycle 0011, where the `data-server` external tree
enters). **Dependency policy (amended 2026-06-10, cycle 0029).** Dependencies
are admitted by deliberate, **per-case review** — what a crate pulls in weighed
against what it buys — with **particular scrutiny for anything that enters the
frozen deploy artifact** (C13: this bot = this commit). Well-established
standard crates (`serde`, `rayon`, …) pass that review and are used wherever
they do the job, including in the bot. There is **no blanket zero-dependency
commitment** and **no blanket admission**; hand-rolling what a vetted standard
crate already does is the anti-pattern, not the dependency. This strikes the
original *"zero-external-dependency by commitment"* clause and the
*"`aura-ingest` is the sole external-dependency firewall"* framing; `aura-ingest`
remains the data-source ingestion edge, no longer a dependency wall.
**Forbids.** Project-specific signals in the aura repo (it keeps at most
example/fixture nodes under `examples/` for its own tests); a multi-project
manager inside aura; a bespoke node registry/marketplace (cargo + Gitea *is* the
package mechanism). (Dependency admission is governed by the per-case policy
above, not a blanket ban.)
**Why.** The engine/game split keeps the engine sharp and reusable while each
project versions its own research with its own forward-queue. Promotion
(local → shared → std) is the ordinary Rust reuse gradient, no new mechanism.
**Realization (cycle 0079, #136 — the analysis leaf becomes its own crate).** The
trading-domain **analysis** layer — the post-run reductions that are pure functions of a
run's recorded data (`RunMetrics`, `RMetrics`, the R reduction `summarize_r` /
`r_metrics_from_rs`, the position-event table `PositionEvent` / `PositionAction` /
`derive_position_events`, and the multiple-comparison hurdle math `inv_norm_cdf` /
`expected_max_of_normals`) — is extracted out of `aura-engine`'s `report` module into a
dedicated **`aura-analysis`** crate (deps: `aura-core` + `serde` only; `serde_json` is a
dev-dependency, test-only). This sharpens the engine↔domain seam: the run loop's crate no
longer *defines* the trading metrics — it `pub use`-re-exports them for source
compatibility this cycle, and still hosts the trace-coupled `summarize`, `RunReport`,
`RunManifest`, and the columnar trace utils. The non-node engine-workspace crates are now
`aura-engine` (run loop), `aura-cli` (`aura` binary), `aura-ingest` (ingestion edge),
`aura-composites` (composite-builder convenience layer), and `aura-analysis` (post-run
domain reductions + selection provenance). Behaviour-preserving (C1): every serde shape
is byte-identical (C18 goldens green).
**Realization (cycle 0080, #136 — engine-side extraction complete).** The last
trading-domain types still *defined* in `aura-engine`'s `report` module — the
selection-provenance types `FamilySelection` / `SelectionMode` — also move to
`aura-analysis` (the only non-cyclic home: `RunManifest.selection` needs the type and the
engine already depends on `aura-analysis`; the registry/CLI reach them unchanged via the
re-export). Behaviour-preserving (C1; suite 665/0). **Settled (2026-06-27, user-ratified
in the #136 thread):** the `aura-registry` `Metric` / `metric_cmp` / deflation vocabulary
**stays in the registry by design** — the registry is the trading *selection* layer, not
the domain-free engine, and its deflation statistics branch irreducibly on metric
identity (R-bootstrap vs. `total_pips` dispersion floor); forcing genericity would be a
one-implementor abstraction. *(Superseded 2026-07-20: measurement's IC became the second
implementor — #290 — and the vocabulary moved behind the `MetricVocabulary` trait
supplied by the outer rungs; see the C28 #147 disposition.)* **Deferred to the World /
C21 layer (explicitly *not* #136):**
making `RunReport` generic over a metric type and turning the orchestration/registry layer
into a reusable domain-agnostic substrate — until then `RunReport` / `RunManifest` /
`summarize` stay trace-coupled in the engine.
**Realization (cycle 0107, #198 — the campaign-execution leaf).** The non-node engine
workspace gains **`aura-campaign`**: campaign-execution *semantics* (cell enumeration,
preflight, gate evaluation, winner selection, walk-forward rolling, realization assembly —
see C18) as a leaf library crate whose deps deliberately exclude `aura-ingest` /
`aura-std` / `aura-composites`; harness construction and data binding enter only through
the one-method `MemberRunner` seam, so consumers (the `aura` CLI today; the playground and
tests tomorrow) bind their own runners while the semantics live here once. It is
explicitly NOT C21's World (a project-side program): it realizes one campaign document
and owns no topology, no data sources, no UI.
**Realization (2026-07-12 — wiring-only tier, #241).** The smallest project
is now data-only: `Aura.toml` + `blueprints/` + `runs/`, no crate. The load
boundary tier-selects (a `[nodes]` pointer list in `Aura.toml` → load that
crate; a root `Cargo.toml` → the pre-#241 native project, unchanged; neither
→ std-vocabulary-only). `aura new` scaffolds the data-only tier;
`aura nodes new` scaffolds a node crate **beside** the project and attaches
it — the visible role-2 switch (C25 role model). Provenance widened
additively: a data-only run stamps commit-only. Invariant 9's "a project is
always a Rust crate" was deliberately amended (user decision, 2026-07-12).

### C17 — Authoring surface
**Guarantee.** All *logic* — nodes, strategies, **and experiments/harnesses** —
is authored in native Rust through **Claude Code + the skills pipeline**: the
human describes, Claude writes the Rust, builds it, runs it via the `aura` CLI,
and reports metrics. Declarative config (`Aura.toml`) carries only **static
project context** (paths only: data archive root, runs dir — cycle 0102),
never logic. aura ships **no embedded coding-LLM**. IONOS LLMs are used only as a
*runtime data source* (news-agent bias, C11), gated by per-session consent,
never in the code path.
**Forbids.** An in-app LLM chat that generates node code inside aura; using
IONOS (weaker models) as the authoring brain.
**Why.** LLMs author Rust well in Claude Code — that is the fix to RustAst's
failure; making weaker models the coding brain reintroduces the very problem.
Keeps aura's scope an engine + playground, not an LLM-IDE.
**Refinement (2026-06-29, #109 resolved — node *logic* is Rust; *topology* is data,
C24).** "All logic … including experiments/harnesses … is Rust" governs
**computation** — a node's math, a meta-program's control flow — and that stays
native Rust (the RustAst lesson, sharpened: a small LLM cannot reliably *apply* a
computational DSL, and a strong one does not need one). It does **not** bind
**topology** — which node feeds which, the structural axes, the param-space — to
Rust *source*. Topology is a **serializable data value** the World owns (C24): a
non-Turing static DAG over the closed, compiled-in node vocabulary (C8/C16),
carrying no computation. This is *not* the RustAst trap re-opened: that trap is a
DSL the author must *apply*; a topology-data blueprint is machine-generated / owned
and applied by no one. The no-DSL guard therefore stands unbroken — it forbids a
*computational* experiment / strategy language, not a static topology-data format.
The experiment-matrix *generator* may stay Rust (C20); its *output* is
topology-data.

### C18 — Project management: one repo = one project, plus a run registry
**Guarantee.** Management has two planes. (1) **Code & forward-queue:** git
(commit = identity; the frozen bot *is* a commit) + Gitea (ideas/hypotheses as
the forward-queue, a research thrust = a milestone, the
`idea → experimental → validated → deployed` label gradient). (2) **Experiments
& results:** an Aura-native **run registry** — one record per run = a *manifest*
(node-commit + params + data-window + seed + broker profile) + *metrics*,
queryable, with *lineage* (composite ← signals; run ← inputs). Determinism
(C1/C12) makes a run reproducible from its tiny manifest, so the registry stores
manifests + metrics and re-derives full results on demand. Depth: **structured**
(promotion/status, lineage, run-diff).
**Forbids.** Storing results not reproducible from a recorded manifest;
duplicating git/Gitea inside aura; a multi-project workspace manager.
**Why.** Comparing experiments over time is the heart of the research loop and
has no home in git/Gitea; determinism makes a structured registry cheap.
Sequencing: the walking skeleton emits a manifest + metrics per run from day
one; the registry/index is a later milestone over manifests that already exist.

**Realization (cycle 0029 — the flat run registry).** The experiments-&-results
plane shipped as `aura-registry`: an append-only JSONL store (`runs/runs.jsonl`),
one serde_json `RunReport` (`RunManifest{commit, params, window, seed, broker}` +
`RunMetrics`) per line, with a typed read-path (`load`) and best-first ranking
(`rank_by`/`optimize`). C9 holds — the registry depends on `aura-engine`, never
the reverse.

**Realization (cycle 0045 — lineage as related records, #70).** The *lineage*
depth is now realized as a **family store**: a sweep / Monte-Carlo / walk-forward
run (the C12 axes) is persisted as a *set of related records* — each a
`FamilyRunRecord` (a `RunReport` stamped with its `family` + `run` + `kind` +
`ordinal`) — in a sibling JSONL (`families.jsonl`), leaving the flat `runs.jsonl`
path and its `append`/`load`/`rank_by`/`optimize` API byte-for-byte unchanged.
the user-facing `family_id = "{family}-{run}"` handle is **derived** from the
stored `family` name plus a per-name `run` index (assigned as a numeric max+1 —
not a content hash; re-running the same family mints a fresh id). `group_families` is the round-trip that re-derives a family
from the stored links (re-listable / rankable as a unit — C21). The manifest *is*
the re-derivation recipe (#71): no input-stream blob / path / payload enters a
record, and a member's window is **producer-supplied** via
`Source::bounds()`/`window_of` (eager or streamed → byte-identical lineage),
never a materialized-`Vec` scan at the call site. CLI surface: `aura mc`,
`aura runs families`, `aura runs family <id> [rank <metric>]`; `aura sweep` /
`walkforward` / `mc` persist via `append_family` with an optional `--name`.
**Realization (cycle 0078 — cross-instrument family + instrument lineage, #146).**
The comparison axis (C12) is realized as a `FamilyKind::CrossInstrument` family:
`aura generalize` runs one candidate across an instrument list and persists the M
per-instrument runs via `append_family`, each member self-identifying through a new
first-class `RunManifest.instrument` lineage field (serde-widened with
`skip_serializing_if`, so legacy lines and every non-cross-instrument path stay
byte-identical — C14/C23). The cross-instrument *generalization score* (worst-case R
floor + sign-agreement + per-instrument breakdown) is a **recomputable aggregate**
over those members, not a persisted family-level record — distinct from #144/#145's
per-winner selection annotation on `RunManifest.selection`.
Deferred (Non-goals): replay-dedup (content-addressed *identity* shipped — #158,
cycle 0094, Realization below); the "run-diff"
depth and ranking families against each other (cross-family, vs. within-family);
and a live producer for the flat `runs.jsonl` standalone-run path — no CLI command
writes it (sweep/walkforward persist to the family store; `aura run` does not
persist). **Resolved (#73, 2026-06): retired** — `aura runs list` / `rank` dropped;
families (C21) subsume standalone over-time comparison. The `aura-registry` flat
lib API is retained: `rank_by`/`optimize` keep live consumers (`optimize` backs
walk-forward's in-sample step, `rank_by` backs `runs family … rank`); `append`/
`load` (the flat-store half) remain public API with **no in-tree caller** after
this retire — tested, available to external consumers, a latent dead-code surface
a later sweep may revisit. **Unknown-id contract (ratified, Runway fieldtest
2026-06).** `aura runs family <id>` treats an unknown-but-well-formed id as an
*empty family* (prints nothing, exit 0) — the same treat-as-empty discipline as
`Registry::load` reading a missing store as `Ok(empty)`, and deliberately
distinct from the retired `list`/`rank` exit-2, which is argv-shape rejection
*before* any store access, not a found-nothing lookup. Tightening to a non-zero
`no such family <id>` exit (typo-safety) is an available future UX choice, not a
current contract.

**Refinement (2026-06-29 — a generated run's topology lives in / is addressed by
its manifest, C24).** The manifest identifies a run's topology today only via
`commit` (this engine + a hand-coded harness) — sufficient while harnesses are a
finite hand-coded menu. Once the World **generates or structurally searches**
topologies (C21/C24), `commit` no longer identifies the graph, so the manifest must
**carry or content-address the topology-data** to stay the re-derivation recipe
(C18's "reproducible from a recorded manifest"). This pulls the previously-deferred
**content-addressed identity** non-goal forward as the natural home for a generated
topology's identity. The format and the carrier are C24's design; recorded here as
the reproduction requirement it must meet.

**Realization (2026-07-01, cycle 0094 — content-addressed reproduction of a generated
run, #158).** A blueprint sweep's topology is now **content-addressed**: the canonical
`blueprint_to_json` bytes are stored once, keyed by the `topology_hash` the manifest
already carries, in a **dumb bytes-by-key store** beside the run registry
(`runs/blueprints/<hash>.json` — `Registry::put_blueprint`/`get_blueprint`, aura-registry;
no `sha2`, no parse — the caller owns the hash, and reproduction's bit-identical compare is
the integrity check). `aura reproduce <family-id>` re-derives every persisted member: load
the member's blueprint by its `topology_hash`, reconstruct the sweep point from the
recorded params, re-run through the **same** `run_blueprint_member` the live sweep uses
(so bit-identity is by construction, C1), and compare metrics — refuse-don't-guess on an
unknown id / missing stored blueprint (exit 2), DIVERGED → exit 1. The manifest + the
content-addressed store + the commit are the complete re-derivation recipe (C18). One
blueprint is stored per family (all members share the signal `topology_hash` — C11/C12
dedup). `aura graph introspect --content-id` exposes the same id for an op-script, via the
one `content_id` primitive `topology_hash` also uses (acc 1); a Tier-1 optional the
blueprint does not use leaves the id byte-stable (acc 3, composing #156/#164).
`serde_json/float_roundtrip` is enabled so stored f64 metrics round-trip exactly through
`families.jsonl` — the precondition for a bit-identical compare (C1). **Signal-only this
cycle**: the id covers the signal blueprint; the fixed r-sma scaffolding stays
commit-identified (it is not yet blueprint-data, C24). Whole-harness / structural-axis
content-addressing remains deferred. The debug-name-in-id question was settled additively
(cycle 0104, #171): the **identity id** — the canonical form with every non-load-bearing
debug symbol blanked (invariant 11), hashed through the same `content_id` primitive and
surfaced as `aura graph introspect --identity-id` beside `--content-id` (combinable) —
makes same-topology blueprints comparable across authoring paths, while the byte-exact
`topology_hash` keeps every role untouched (introspection-only: no manifest field, no
store key until a dedup consumer exists). Reproduction is proven on
synthetic (deterministic) data; recorded-dataset reproduction rides the DataServer seam
(#124). **Cycle 0095 (#170):** `aura reproduce` now also spans `FamilyKind::MonteCarlo` —
branching on the family kind, it reconstructs each member's seed-driven synthetic walk from
the recorded `manifest.seed` (the `Sweep` arm unchanged), so an `aura mc` family re-derives
bit-identically through the same `run_blueprint_member` path. **Cycle 0097 (#173):** reproduce
spans the third variant, `FamilyKind::WalkForward` — the same branch rebuilds each OOS member's
windowed slice from `manifest.window` (winner params via the shared `manifest→cells` recovery),
so an `aura walkforward` family re-derives bit-identically too. All three family kinds now
persist *and* reproduce through the one shared `topology_hash`+`put_blueprint` hook.
**Realization (cycle 0106, #189 — research-artifact document stores).** The registry's
content-addressed store family grew two siblings beside `blueprints/`: `processes/` and
`campaigns/` hold the two research-artifact document types shipped by the #188 role-model
pass — the **process document** (role 5: a named validation/eval methodology, a closed std
stage vocabulary wrapping shipped primitives) and the **campaign document** (role 6b:
persisted experiment intent — instruments × windows × strategy refs by content/identity id ×
param axes × process ref (content-id-only) × data-level presentation). Documents are
canonical JSON (`format_version` envelope, omit-defaults, no trailing newline) keyed by the
**shared content-id primitive, now library-hosted** (`aura_research::content_id_of`;
`aura-cli`'s `content_id`/`topology_hash` delegate byte-identically — the id goldens pin the
move). Unlike `put_blueprint` (caller owns the hash), the document puts self-key from
canonical bytes; gets are `Ok(None)` treat-as-empty. The **referential tier**
(`validate_campaign_refs`) resolves process/strategy refs against the stores (identity refs
by store scan in this cycle; index-first since #191, below) and checks each campaign axis — name AND declared `ScalarKind`, the axis
carries its kind once — against the referenced blueprint's `param_space`. Campaign P1
control constructs (axes/gates/ladders per #188) carried intent only in this cycle: no
executor existed yet — executor need was re-tested against the intent-persistence
diagnosis (#189 triage, decided item 6; the cycle-0106 fieldtest F7 verdict was that
evidence), and the v1 executor shipped the next cycle (below).
**Realization (cycle 0107, #198/#196 — the campaign executor and its realization store).**
`aura campaign run <file|content-id>` executes a campaign (a file is register-then-run
sugar; the content id is canonical): zero-fault referential gate, then the process
pipeline — v1 executable shape `std::sweep [std::gate]* [std::walk_forward]?`
(`std::monte_carlo`/`std::generalize` refused loudly at preflight in this cycle; they
execute since cycle 0108, below) — runs once per (strategy, instrument, window) cell in
doc order. Execution
*semantics* live in the **`aura-campaign` library crate** (#198 home decision: reachable
beyond the CLI; NOT C21's project-side World): grid odometer over the campaign axes,
members through the engine `sweep` over a **`ListSpace`** (explicit point set beside
`GridSpace`/`RandomSpace` — a gate's survivor subset has no cartesian structure),
per-member gates via the 14-name `member_metric` roster (an R-predicate over a missing R
block fails conservatively), walk-forward re-rolled in the doc's epoch-ms unit
(`WindowRoller`; IS windows search ONLY the survivor points; OOS winner reports carry
`manifest.selection`), deflation nulls seeded from the doc's `seed` (C1: realization is a
pure function of doc + stores + data). Harness/data binding stays consumer-side behind the
one-method **`MemberRunner`** seam — the CLI binds the shipped loaded-blueprint reduce
convention with unique suffix-join of raw axis names onto the wrapped `param_space`. The
registry grew the **`campaign_runs.jsonl`** JSONL sibling (beside `runs.jsonl` /
`families.jsonl`): one thin `CampaignRunRecord` per run — campaign/process ids, seed, and
per-cell realized stage prefixes linking family ids, gate survivor ordinals, and sweep
selections — over untouched family records, run-counted per campaign id. Zero survivors
truncate a cell's realized prefix and exit 0 (a null result is a valid research result);
`emit` is honored (`family_table`/`selection_report` lines); `persist_taps` was deferred
LOUDLY on stderr in this cycle (the wiring shipped in cycle 0109, below). The **blueprint on-ramp** (#196) closes
the F5 authoring gap: `aura graph register` (store put keyed by content id == topology
hash), `aura graph introspect --params` (the RAW `param_space` namespace campaign axes
are validated against), and a blueprint-file mode on `--content-id`. The
`std::walk_forward` vocabulary was corrected to machinery-true fields
(`in_sample_ms`/`out_of_sample_ms`/`step_ms`/`mode` — `WindowRoller`'s three lengths and
both `RollMode`s; the shipped `folds` slot mapped to nothing the machinery accepts), with
a new `ZeroWalkForwardLength` intrinsic fault; wf-bearing process docs get new content ids
by design (the 0106 fieldtest corpus stays as the historical record). Known debt:
metric-roster triplication (still hand-maintained, but drift from the shipped
`aura-analysis` types is now test-caught by a cross-crate guard, #190;
single-source removal waits on #147), deflation-constant duplication (#199).
**Realization (cycle 0108, #200 — the annotator stages execute).** The v2 executable
shape is `std::sweep [std::gate]* [std::walk_forward]? [std::monte_carlo]?
[std::generalize]?` — an ordered optional annotator suffix, each at most once,
`std::generalize` strictly last; the executor preflight refuses what the intrinsic tier
deliberately admits (`[sweep, mc, walk_forward]` is intrinsically valid — the tier
boundary is test-pinned on both sides), plus three new static guards
(single-instrument generalize, non-R generalize metric via the registry's
`check_r_metric`, zero mc `resamples`/`block_len`). **Both annotators are terminal**
(unanimous #200 triage): nothing flows out of them; filtering stays the gate's monopoly.
`std::monte_carlo` bootstraps the stage's *incoming R-evidence* with one semantics,
input-shaped by position — after a walk_forward, ONE `r_bootstrap` over the wf family's
pooled per-window OOS `net_trade_rs` in roll order (`PooledOos`; #259 materialized this
conduit as the cost-netted per-trade series `r − cost_in_r`, equal to the gross series
bit-for-bit when no cost model is bound); after sweep/gates, one `r_bootstrap` per
surviving member's fresh in-memory series (`PerSurvivor`, ordinals into the population
family; a zero-trade member records the engine's defined all-zero degenerate) — seeded
from the campaign doc's `seed` (C1; `net_trade_rs` is `#[serde(skip)]`, so annotators run
in-executor or not at all). `std::generalize` executes at **campaign
scope**: after all cells, per (strategy, window) the per-cell *nominees* (last wf
window's OOS report, else the sweep winner; none on gate truncation) across instruments
feed the shipped `generalization()` when ≥ 2 exist — divergent per-instrument winners
are exposed via their params, never averaged away; a shortfall is recorded, not computed
around. Realization: `StageRealization.bootstrap` (`StageBootstrap::PerSurvivor |
PooledOos`) and `CampaignRunRecord.generalizations` (`CampaignGeneralization` keyed
strategy × window with `winners`/`missing`), both serde-default sparse — pre-0108
`campaign_runs.jsonl` lines parse unchanged (C14/C23). No document content id moved
(introspection doc-strings dropped "in v1" only). Noted debt: the mc arm detects the wf
family by the stringly `block == "std::walk_forward"` literal (a pre-existing lockstep
pattern with the realization's block strings).
**Realization (cycle 0109, #201 — persist_taps wired).** Campaign presentation persists
traces: the tap namespace is a **closed vocabulary** of the wrap convention's four sink
names (`equity`/`exposure`/`r_equity`/`net_r_equity`; `aura_research::tap_vocabulary`,
intrinsic `DocFault::UnknownTap` — the escalation for a new observable is a new
vocabulary entry or an authored blueprint sink, never an open node-path namespace).
Scope is the per-cell **nominee only**: after the pipeline settles, the CLI re-runs each
nominee once in non-reduce mode (all four channels drained; windowed to the nominee
manifest's own ns bounds) and **asserts metrics equality** against the recorded nominee —
the C1 drift alarm, hard refusal on divergence (the reproduce precedent, enforced).
Traces land in the existing TraceStore as
`traces/{campaign8}-{run}/{strategy8}-{instrument}-w{n}/{tap}.json`
(`ensure_name_free(Family)` once; window ordinal doc-derived), chartable by the unchanged
viewer. The record carries ONE sparse pointer, `CampaignRunRecord.trace_name`
(`Some("{campaign8}-{run}")` iff the doc requests taps — the claim-sentinel contract:
`execute` claims, `append_campaign_run` composes the name via the single-sourced
`derive_trace_name`, `execute` mirrors it onto the returned copy). Loud lines replace
the retired deferral: per-cell no-nominee skip, per-run unproducible-tap skip
(`net_r_equity` needs a cost leg; the campaign runner wires none), one summary.
`aura-campaign` stays trace-agnostic (the MemberRunner seam is unchanged; the stamp is a
pure name derivation). Noted debt: `aura chart` over the campaign family ROOT (cells
spanning instruments) is untested/semantically undefined — only per-cell read-back is
pinned.
**Realization (#272, 2026-07-14 — per-cell fault isolation).** A member
fault (no-data, bind, run, or a caught panic) is a recorded per-cell outcome,
never a global abort: `run_cell` returns a fault-annotated `CellRealization`
(`fault: Option<CellFault>`, closed `CellFaultKind`) instead of `Err`, so
`execute`'s existing accumulate-then-append-once tail persists every healthy
cell and the one run record. Containment granularity is the cell for a sweep
stage (a grid hole compromises selection) and the fold for walk_forward
(surviving folds pool; failed folds recorded as `StageRealization.
window_faults`, the summary naming the ratio). `ExecFault::Registry` and
doc-shape preflight faults stay global. The CLI declares holes (per-cell
notes + a completion summary) and a run with ≥1 failed cell exits **3**
("completed with failed cells" — distinct from 0/1/2). A partially-covered
window carries a `CellCoverage` annotation (effective bounds + interior gap
months, from the #264 archive primitives). Generalize already treats a
no-nominee cell as `missing`, so a failed cell surfaces there unchanged.
Member panics are caught with `catch_unwind`(`AssertUnwindSafe`) at the three
member-run sites and recorded as `MemberFault::Panic`; a ref-counted
`SilencedPanic` guard (a process-global panic-hook save/no-op/restore behind a
`static Mutex`, held only around each `catch_unwind`) suppresses the default
crash backtrace so "recorded, campaign continues" is observably true on stderr,
not merely true in the record. The guard's mutex serialises only the
ref-count/hook-swap (O(1)), never the member computation, so C1 disjoint-parallel
execution and determinism are preserved; ref-counting (save on 0→1, restore on
1→0) keeps concurrent sweep/walk-forward threads and any caller-installed hook
correct.
**Realization (#191, 2026-07-17 — identity-ref resolution is index-first).**
`find_blueprint_by_identity` no longer re-loads the whole blueprint store per
reference: a fourth persistent JSONL sidecar, `blueprint_identity_index.jsonl`
(identity id → content id; fixed-name sibling of the runs store, appends under
the #276 lock), is consulted first, and every hit is **verified** by loading
that one blueprint under the current resolver and recomputing its identity id —
the index is a cache, never an oracle, so resolution results stay
scan-identical under roster drift, store surgery, or index corruption (the one
unspecified corner is unchanged in kind: which same-identity twin answers was
`read_dir`-order-dependent before and is index-history-dependent now). Any miss
or failed verification runs the old scan as a **full-store repair pass**,
collect-then-diff-append: the walk's last-wins mapping is diffed against the
pre-walk snapshot after the walk, so a converged index — twin stores included —
appends nothing (the twin-convergence pin). Index reads never fail a lookup
(missing/unreadable file → empty, unparseable lines skipped), repair appends
are best-effort, and a pre-index store backfills itself on its first miss, no
migration; a read-only store keeps scanning as before. Write paths, the engine,
and both callers are untouched; maintenance is lazy-only — put-time indexing
was rejected because it would need a roster-free doc-level identity function
whose equivalence to the loaded-composite path no green test ratifies (decision
log: #191 comments).

### C19 — Bootstrap: blueprint → instance (recursive)
**Guarantee.** Construction is a distinct phase, recursive at every level. Each
node type has a **factory** `params → sized concrete node` (e.g. `SMA(length)`
sizes its ring buffer). A **blueprint** is the param-generic, input-role-generic
graph-as-data produced by running a Rust builder (C9); it carries *free* numeric
params (declared ranges) and *free* input roles. The **bootstrap** binds
`(blueprint + param-set + data bindings + seed)` into a concrete, **frozen
instance** — buffers sized, topology fixed. This is precisely the "wiring /
graph build" that C7 ("sized at wiring", "topology frozen per sim") and C12
("params injected at graph build") already reference. The same machinery applies
recursively up to the harness (C20). A sweep builds many instances from one
blueprint; instances are disjoint (C1).
**Forbids.** Params that change topology (a topology change is a *different*
blueprint — Fork A, C7 "frozen"); resizing buffers after bootstrap; running a
sim against an un-bootstrapped blueprint.
**Why.** Separating the param-generic blueprint from the param-bound instance is
what makes one strategy reusable across a whole sweep and lets the optimizer
mutate "the 20" by *rebuilding* an instance (cheap; no recompile, C12) instead
of rewriting code. Naming the build phase makes the implicit "wiring" of C7/C12
explicit.
**Refinement (Construction-layer milestone, 2026-06-05).** This binding is a
**compilation**: the param-generic, named blueprint (source) is lowered to a flat,
type-erased **flat graph** (C7) **wired by raw index, not by name**
(`Edge { from, to, slot, from_field }`): composite boundaries dissolve entirely,
and field / role names are demoted to **non-load-bearing** debug symbols (as
`FieldSpec.name` already is). "No recompile" above means no **Rust /
cdylib** rebuild (C12/C13: the cdylib loads once); re-deriving an instance per
param-set is a cheap **graph re-compilation**, not a code recompile. Naming the
build phase a compilation makes its successor explicit: the flat graph is the target
of behaviour-preserving optimisation (C23).
**Refinement (#275, 2026-07-15).** One narrow exception to "role names demoted to
non-load-bearing": a `SourceSpec.role` (the lowered bound-`Role` name) is
**load-bearing for source binding** — the key `Harness::run_bound` / `bind_sources`
resolve a keyed source supply against. Every other flat-graph name (edges, ports,
composite boundaries) stays a non-load-bearing debug symbol; the raw-index
positional `run` path carries no role.
**Realization (cycle 0016 — param-set injection).** The bootstrap now binds an
injected param-set, realizing C12's "params injected at graph build (the optimizer
sees a generic vector of typed ranges)" and C19's "factory `params → sized node`"
*literally*: a blueprint leaf is **value-empty** — `BlueprintNode::Leaf` holds a
`LeafFactory { name, params, build }` recipe, not a built node — and the value lives
only in the injected vector (no baked default), so the blueprint stays a pure
param-generic recipe. (Renamed in cycle 0024: `BlueprintNode::Primitive` holds a
`PrimitiveBuilder { name, schema, build }` — the recipe now carries the full
signature, see the C8 0024 realization; `bootstrap_with_params`/`compile_with_params`
moved onto `Composite` when `struct Blueprint` collapsed into it, see the C19 0024
realization.) `bootstrap_with_params(Vec<Scalar>)` /
`compile_with_params` **build each leaf through its own constructor** (the single
sizing/validation gate) from its kind-checked slice **while lowering** (build-then-
wire), consuming the vector slot-by-slot in the *same* depth-first walk
`param_space()` projects — so the two share one traversal (subsuming the #34 dual-
traversal hazard) and the value reaches the node at the slot the sweep enumerates.
Arity is checked up front (`param_space().len()`); a wrong-kind or wrong-length
vector is a typed `CompileError::{ParamKindMismatch, ParamArity}` (the typed-value
check C8 deferred). The lowering/edge/source rewrite is structurally unchanged, so
the **flat graph stays bit-identical** for a given point (C23, the correctness
invariant). The value *domain* (e.g. `length ≥ 1`) stays the constructor's own
`assert`; the search-range is still the run's (#32/C20). One value-empty leaf
detail for C22: the blueprint view (pre-run, param-generic) labels a leaf by **bare
type** (`PrimitiveBuilder::label`, was `LeafFactory::label`, → `[SMA]`) — the
value-bearing `SMA(2)` of C8's render-
label refinement now appears only in the *compiled* view (built nodes, `Node::label`).
**Realization (cycle 0017 — blueprint render = main graph + definitions).** The
`aura graph` blueprint view (C9 graph-as-data, #13) renders the **authored
structure** as a *program with subroutines*: a flat **main graph** wiring the
harness with each composite shown as a **single opaque node** `[name]`, plus a
`where:` section that defines each **distinct** composite type **once** (its
interior with named input-entry nodes and outputs folded onto their producers as
`name := …` bindings (render refined through cycles 0019–0022; originally
`[in:k]`/`[out]` port markers); deduped by `name()`, collected
recursively so nested composites are opaque nodes with their own definitions). This
supersedes #13's original cluster-box model and is the durable split this view
realizes: **blueprint = source** (composites as named subroutines, body once) vs.
**compiled = inlined machine form** (C23, boundary dissolved). The substantive cause
for retiring cluster boxes is a real renderer defect — `ascii-dag` 0.9.1's subgraph
level-centering rounds sibling x-positions with `/2`, overlapping wide sibling
labels (width/parity-sensitive, no config/padding dodge surviving unequal-width
siblings); the **flat** layout is collision-free, and both views now build flat
graphs only. The model also scales (blueprint size tracks top-level wiring, not
inlined node count) and removes #13's nested-composite `unimplemented!` (the
definitions pass recurses). The interactive *enter/focus* counterpart (a composite
collapsed to a navigable node) is the playground's, parked as a separate concern
(#37); the static CLI keeps the all-at-once definitions form (#38).

**Realization (cycle 0024 — the root is the fully-bound composite; the flat graph is
a named type).** `struct Blueprint` is **deleted**: the root graph IS a `Composite`,
and `compile_with_params`/`bootstrap_with_params`/`param_space` are its methods.
What distinguished the root — its bound data sources — is now a property of its input
roles: `Role` carries `source: Option<ScalarKind>` (`None` = an open interior port,
wired by the enclosing graph; `Some(kind)` = a bound ingestion feed). A composite is
**runnable iff every root role is bound** (C3: sources bind at ingestion only); an
open root role is a compile-time `CompileError::UnboundRootRole`. So the "main graph"
is no longer a separate kind — only the composite all of whose roles are
source-bound, governed by the same conditions as any other node. Compilation now
targets a **named type**: `compile` validates structurally **pre-build** (via
`signature()`, no node constructed — an ill-typed wiring is caught before any build
closure fires) and emits `FlatGraph { nodes, signatures, sources, edges }` — the
C23 flat graph, now first-class — which `Harness::bootstrap` consumes (kinds/firing
from the carried signatures, buffer depth from `lookbacks()`). The per-flat-node
signature travels beside the node, so `bootstrap` reads it without a built-node
`schema()` call (which no longer exists, see the C8 0024 realization).

**Realization (cycle 0026 — graph render redesign: model + WASM-Graphviz viewer,
#51).** `aura graph` no longer renders ASCII. The render path is now two pieces:
a read-only **model serializer** (`aura_engine::model_to_json`, iteration 1) that
walks the root composite + every distinct composite type into a deterministic,
hand-rolled JSON model (C14, golden-tested; the engine's last hand-rolled JSON
writer after `RunReport::to_json` moved to serde in cycle 0033; the
swapped-param mis-wire property moved here from the old compiled-view test), and a
**self-contained HTML viewer** (`aura-cli::render::render_html`, iteration 2) that
inlines that model, the ported prototype viewer JS, and a vendored Graphviz-WASM
blob into one page emitted to stdout. Layout/SVG happen in the browser via
WebAssembly — aura ships no layout engine and stays a serializer (C9: graph-as-data,
no `eval`/build on the path). The viewer is a render asset (C10 — no node/strategy
logic, no DSL); it labels every input pin from the model's now-real names (C23
debug symbols, named in cycle 0027) and colours wires by the four scalar base
types (C4). This **retires `ascii-dag`** and its adapter (`graph.rs`), the
`--compiled`/`--macd` flag plumbing, and the invented `#Sf`/`:=`/`histogram →`
notation — superseding the cycle-0017 flat-ascii model and its renderer-defect
workaround. The DOT/SVG are Graphviz-version-dependent and not golden-tested; the
deterministic JSON model is the asserted contract.

**Realization (cycle 0034 — structural-constant bind: a knob *removed* from
param_space, #55).** `PrimitiveBuilder::bind(slot, value)` adds the **third** param
category beside the topology factory-arg (C7/C19) and the tuning param (the
cycle-0016 value-pin): a **structural constant**. The cycle-0016 binding *pins* a
value in the injected vector while the knob **stays** in `param_space` (a tuning
param the sweep varies); `bind` instead **removes** the slot from `param_space`
entirely — the knob is gone, not fixed. The discriminator is the #55
deform-vs-tune test: a value whose variation yields another valid point of the
*same* strategy is a **tuning param** (stays in `param_space`); a value whose
variation *deforms* the strategy into a different one (e.g. the `2` of an
"SMA2-entry" bound to its two-candle construction) is a **structural constant**
(bound out), so a sweep never enumerates deformed strategies as valid family
members. Mechanically `bind` shrinks the builder's declared param surface
(`schema.params`) and wraps its build closure to re-splice the constant at its
original positional slot; the construction layer
(`collect_params`/`lower_items`/`param_space`/`compile_with_params`) is
**byte-unchanged** — both dock sites already key off `builder.params()`, so the
shrink propagates for free, and chained binds reconstruct the correct positional
vector because each layer computes its slot index relative to the param list it
sees. C23 is unaffected: `bind` resolves the param **name** to a position at
**authoring** time (the by-name authoring address space, the 0032 amendment) and
the flat graph stays wired by raw index — the name never reaches it. The
complementary question — exporting a **named frozen** strategy (all/most knobs
bound) as a reusable blueprint *value* — is deferred (#60); `bind` ships only the
per-knob overlay, no registry (C9/C10 intact).

### C20 — Strategy ↔ harness; the harness is the root sim graph
**Guarantee.** A **strategy** is a reusable composite-node blueprint (C9):
broker-, data-, and viz-independent, with inputs declared as named **roles**
(symbol-agnostic where possible) and the **bias** stream (C10) as output.
A **harness** (the experimental setup) is the **root sim graph** — sources bound
to the strategy's input roles + the strategy + attached broker node(s) + sinks —
and is itself produced by the bootstrap (C19). A harness *instance* is C1's
disjoint unit (RustAst's "root scope"). The harness has **two kinds of
parameterization**: **structural axes** (which strategy, which instrument(s),
which broker(s), which window, which **risk regime**) whose variation selects
*different* instances — the **experiment matrix** (the risk regime is the fourth
axis, realized 2026-07-06 / #210 as `CampaignDoc.risk`; see the C10 realization
for its kept-separate, compared-not-selected semantics); and **tuning params**
(the strategy's numeric params)
swept *within* a fixed structure (Fork A). The same strategy blueprint is reused
across backtest, sweep, visual workspaces, and the frozen live bot — each a
different harness. **Both strategy and harness/experiment are authored in Rust**
via builder APIs (C17); the experiment matrix is ordinary Rust control flow
(loops/conditionals), not a config schema. Ontologically, a node (incl. a
strategy composite) is an **open** fragment — free input roles + ≤1 output
(C8/C9) — that does not run alone; a **harness is the closed root graph**: a
strategy with its input roles bound to sources and its output terminated in
broker/sink nodes, under a clock. A harness is therefore **not a node** (no free
inputs, no output; it does not fit `eval`) — it is the *closure that runs*, C1's
disjoint unit / the root scope. Harnesses do not nest as nodes; the World (C21)
orchestrates them as objects.
**Forbids.** Embedding data sources / brokers / sinks inside a strategy; a
declarative experiment mini-DSL (logic is Rust — C17); modelling the harness as
a node (it is the closed root scope, not an open composable node).
**Why.** Reusability needs the strategy to be a context-free blueprint that many
harnesses embed. Modelling the harness as a root graph keeps it within the one
Node/graph abstraction (C9) and makes "10 strategies in one environment" and
"one strategy × N instruments" plain nested loops over the structural axes. Rust
authoring (not config) preserves full programmatic power — conditional/adaptive
matrices, generated axes, custom wiring — and avoids re-introducing the DSL trap
C17 rejects.
**Realization (GER40 session-breakout blueprint milestone, 2026-06-17 — refs
#94/#96/#97, spec 0051).** Made concrete on the first real-data strategy: a
**hand-wired `FlatGraph` is not a shippable strategy** — it carries no
`param_space()`, so the World families (sweep / walk_forward / compare, C21)
cannot consume it without a hand re-author (the friction the GER40 deep-dive
fieldtest surfaced). The **canonical shippable form is the `Composite`
blueprint** (the authoring/source level, C9/C19); the `FlatGraph` is only its
compiled substrate (C23). The breakout now ships as
`ger40_breakout_blueprint(bar_period, …)` whose `param_space()` is exactly its
tuning knobs (`{entry_bar.target, exit_bar.target}`); the **bar period is a
construction argument** binding Resample + Session together — a structural
matrix axis (C12: a different period is a *different strategy*, not a sweep
point), never a `param_space` entry, so a sweep cannot desync the two clocks.
This is the concrete instance of the structural-axis-vs-tuning-param split
above (and `delay.lag`, a C8 structural constant, is bound out of the space).
**Refinement (2026-06-29 — experiment-matrix *members* are topology-data, C24).**
"The experiment matrix is ordinary Rust control flow, not a config schema" holds for
the **generator** — the loop / conditional that *enumerates* structural variants may
stay Rust (C17). But each **member** it yields is a **topology-data value** (C24),
not a hand-coded blueprint nor engine-baked source: a structural axis selects among
*data* blueprints the World constructs, mutates, and serializes. This is what makes
structural variation **first-class and searchable** rather than a hand-enumerated
menu — `HarnessKind` and the per-strategy `*_sweep_family` functions in `aura-cli`
are the pre-C24 scaffolding (topology-as-engine-source, a C16 tension), retired as
C24 + the project-as-crate layer land. [C26 realization, 2026-07-10 (#231): the
scaffolding's last data weld — `wrap_r`'s hard-wired `price`←close role and the
`M1Field::Close`-only open sites — is retired; a strategy's input roles now bind
archive columns by name (C26). `wrap_r`'s remaining R-scaffolding retirement
stays #159.]
**Refinement (2026-07-03, #188/#189 — experiment INTENT is campaign-document data).**
The "ordinary Rust control flow, not a config schema" clause and the forbids-clause
"declarative experiment mini-DSL" are scoped by the #188 role-model pass: they forbid an
open, logic-bearing experiment language (the RustAst trap), **not** the closed-vocabulary
**campaign document** (C25/C18) that now carries persisted experiment intent — data
windows × strategy ids × param axes × process ref under the total, declarative P1
construct tier (bounded axes, gates, ladders; no variables, no general recursion, no
unbounded iteration — invariant 5's no-free-feedback move applied one level up). A
*generator* that enumerates structural variants may still be plain Rust (role 2/6a
technique); what it yields, and what a campaign declares, is data. Genuinely new logic
(metrics, analysis blocks) escalates to a new Rust block (role 2), never to a freetext
hole in the artifact.

### C21 — The World: the meta-level is the product
**Guarantee.** Above the harness sits the **World** — the project's program /
"game" (C16: a Rust crate). Within it, **harnesses are dynamically constructible,
first-class objects**: meta-programs (walk-forward, sweep, optimize,
Monte-Carlo — C12's axes) construct harness instances at runtime via the
bootstrap (C19), run them disjointly in parallel (C1), aggregate / compare their
results, and discard the transient instances. A walk-forward rolls windows →
bootstraps a harness per window → stitches out-of-sample equity + parameter
stability into one meta-result. Orchestrating *families* of harnesses is
**first-class**, not a headless afterthought; the run registry (C18) is the
World's memory.
**Forbids.** Relegating multi-harness orchestration (walk-forward / sweep /
comparison) to second-class headless-only status; treating the single backtest
as the product.
**Why.** What happens *within* one harness — backtest a strategy → equity — is
commodity; every quant system covers it. aura exists for the meta-level: a
programmable space where harnesses are dynamically built and families of them
orchestrated and explored. The deterministic single-harness engine (C1–C20) is
the **substrate**; the World is the **product**.
**Refinement (2026-06-29, #109 resolved — the World owns topology as data, C24).**
"Harnesses are dynamically constructible, first-class objects" is sharpened: their
**topology is a serializable data value the World owns** (C24), not Rust source.
This is the precondition for the World's full ambition — it can **generate**,
**mutate**, **structurally search** (genetic / NEAT-style graph operators, the open
search-policy thread), **compare**, and **serialize-for-reproduction** (C18)
*families that vary structure*, not only numeric params. A param sweep over a fixed
skeleton is the degenerate case; varying the skeleton itself needs
topology-as-value. The game-engine principle (C16) made literal: the engine owns the
scene / blueprint graph as content, instantiates and runs it, the way aura owns
harness topology as data.

### C22 — The playground is a trace explorer; sinks are the recording mechanism
**Guarantee.** The World is a *program*: nothing is displayable until it runs,
and its harnesses are transient machinery (built, run, discarded — C21). The only
durable, displayable substance is the **recorded trace**, captured by **sinks** —
pure consumer nodes (C8) that persist a stream (equity, position events, a node's
output) into the run registry (C18). **Displayable = exactly what a sink
recorded**; with no sink, only input params + summary metrics remain. The
**playground** is therefore an **execution viewer / trace explorer**, and it
plays *any* harness (it is the harness *player*, not a harness, never bound to a
default one): before a run it shows the program *structure* (graph-as-data, C9) +
param knobs; during a run, live sink streams; after a run, recorded traces +
metrics from the registry — including meta-views (stitched walk-forward, sweep
surfaces, multi-strategy / instrument comparison). Observability is **explicit
and selective** — you instrument what you want to see; the choice of sinks is
part of the experiment. The engine ships sample harnesses *with* sinks so a
newcomer sees a populated trace immediately; a fresh project is empty until
built, run, and instrumented.
**Forbids.** A scene-editor model that assumes a persistent populated world;
constructing or wiring topology in the UI (topology is Rust + hot-reload,
C9/C17 — the UI reflects the live graph-as-data and tunes runtime params via
sliders, C12); retaining un-sinked data; binding the playground to a single /
default harness.
**Why.** A program has no scene-at-rest to inspect; what persists is what it
records. Making sinks the one recording-and-observability mechanism keeps "what
can I see?" answerable by "what did I instrument?", and keeps the engine
UI-agnostic (C14). Live param tuning (runtime values, no topology change —
C12 / C19 Fork A) gives the interactive feel without a wiring DSL.
**Realization (cycle 0006).** Sinks-as-recording-mechanism is realized at the
substrate level: a recorded trace is exactly what a recording node pushed out of
the graph (no engine recording registry; the constructing World holds each
recording node's destination). The engine's single `observe: usize` affordance is
removed — `Harness::run` returns `()` and recording is a node-side concern, so one
run records *many* streams (one per recording node) instead of exactly one row.
Recorded streams are sparse and timestamped (a record per fired cycle, tagged
`ctx.now()`), matching a trace of timestamped events (C18). No new contract; the
`Harness` API change (observe removed, `run -> ()`) is recorded here.
**Realization (the web-from-disk visual face, #101).** The C14/C22 web seam shipped
(amendment 3b56efb): a recording run persists each drained tap as a columnar (SoA,
C7) `ColumnarTrace` to `runs/traces/<name>/` (`aura-registry::TraceStore`, beside the
run registry's `runs.jsonl`), reachable via `aura run [--real <SYM> …]
--trace <name>`; `aura chart <name> [--panels]` reads them back, aligns all taps on a
synthetic-union timestamp spine via the post-run `join_on_ts` (C3 — not in-graph;
C1 — pure, no live external call), and emits a static self-contained uPlot page
(vendored like `render_html`'s Graphviz-WASM). The engine stays headless (C14):
encoding lives in `aura-engine` (`ColumnarTrace`, struct→JSON only), file I/O in
`aura-registry`, rendering in `aura-cli` (`render_chart_html` + `chart-viewer.js`).
First cut only — overlay (per-series y-scale) / timestamp-aligned panels; the served
page injected the chart *series* but no run-context header (the run manifest is
persisted on disk in `index.json`, deliberately not surfaced in that first cut — a
ratified scope call). The header (#102) and serve-time decimation (#108) landed in
cut 2 (see the served-page-hardening amendment below); the families-comparison view
landed too (#107). A local server and replay-clock controls remain open (see "Open
architectural threads").
**Amendment (family-member traces, #104, d3cb5f8).** The disk-trace layout extends
to family runs: `aura sweep|mc|walkforward --trace <name>` persists *each member* as
a nested standalone run-dir `runs/traces/<name>/<member_key>/`, reusing
`persist_traces`/`TraceStore` verbatim (engine untouched — persistence is a
side-effect inside each per-member closure). The `member_key` is content-derived and
deterministic — sweep: the *varying* axes rendered as a filesystem-portable
directory component (`<axis-name>-<value>` tokens joined by `_`, charset
`[A-Za-z0-9._-]`, case-less values, length-capped with an FNV fallback), MC
`seed{N}`, walk-forward `oos{ns}` — never
a runtime ordinal, because members run in parallel under the engine's `Fn + Sync`
HOFs, where a counter would be schedule-dependent (C1); concurrent `TraceStore::write`
targets disjoint member dirs, so it is lock-free. Opt-in: without `--trace`,
stdout/registry are byte-unchanged. Because `TraceStore` resolves `<name>/<member_key>`
as a subpath, `aura chart <name>/<member_key>` charts any single member with no
view-side change — the write-side precondition for the family-comparison **view**
(overlay / small-multiples across members) — now realized (#107; see the
families-comparison amendment below).

**Amendment (CLI `--trace` retired, #168 / #224).** The CLI-verb `--trace` story above (single-run `run --trace`, amendment 3b56efb; per-member `sweep|mc|walkforward --trace`, #104) describes capabilities that no longer reach the code. `run` and `mc` refuse `--trace` (structurally parseable, refused at dispatch); the per-member family `--trace` was never wired to the blueprint sweep (`run_blueprint_sweep`'s `let _ = persist`) and was silently dropped when the welded `--strategy` triple retired (#159/#220). #168 makes the surface honest — `sweep`/`walkforward --trace` now refuse up front (exit 2, forward-pointer to #224). The single live `TraceStore::write` site is the campaign `presentation.persist_taps` → `runs/traces/<name>/` (`persist_campaign_traces`); `aura chart <name>` reads that back. Restoring CLI-side per-member trace-writing is deferred to #224. **[Delivered 2026-07-11 (#224 + fieldtest B1 fix): `sweep`/`walkforward --trace` now WRITE per-member traces on the real-data campaign path (the depth-2 fan-out `runs/traces/<name>/<cell>/<member>/`), refusing only on the synthetic path; `aura chart <family handle>` resolves both the depth-1 campaign layout and the depth-2 fan-out (members keyed `<cell>/<member>`, C1-sorted). The refusal story in this amendment is historical.]**

**Amendment (real-data family source, #106, 8e5d14b).** The family runs gain an
**opt-in real-data source axis**: `aura sweep|walkforward --real <SYMBOL> [--from
<ms>] [--to <ms>]` streams real M1 close bars from the data-server archive (the #71
`M1FieldSource` seam — C6 record-then-replay: a pre-recorded archive, never a live
call mid-sim) instead of the built-in synthetic stream, per family member. A
CLI-side `DataSource` provider (synthetic | real) supplies each member's source,
pip (resolved from the recorded geometry sidecar (`instrument_geometry`) — C10
refuse-don't-guess; a symbol with no recorded geometry exits 2 before any data
access), window, and — for walk-forward — its `WindowRoller` sizes
(synthetic: bar-index 24/12/12; real: fixed calendar-time 90d/30d/30d in ns; CLI
flags for these are deferred). **[Amended 2026-07-11 (#239): on the dissolved
`walkforward --real`/`mc --real` sugar path the fixed 90/30/30 sizes are a
*ceiling*, not a constant — `fit_wf_ms_sizes` (aura-cli) passes them through
byte-identically whenever they fit the resolved campaign window, and scales them
down preserving the 3:1 IS:OOS ratio (step = OOS, one roll at the minimum) when
the window is shorter; authored process documents still validate their declared
sizes as-is.]** The engine, ingest, and registry are untouched (C9 —
the whole change is in `aura-cli`); the synthetic path is byte-unchanged.
**MC is excluded** (#106 Fork A): its seed varies a *synthetic* price-walk
realization (C12 axis 4), which is undefined over real data's single realization —
`aura mc --real` refuses with exit 2; a real MC needs a bootstrap-resampling axis
(its own cycle). The real walk-forward member key `oos{from.0}` widens from a small
synthetic bar index to an epoch-ns integer (still portable, collision-free). The
built-in demo strategy's **length grid is likewise data-kind-dependent**
(`DataSource::strategy_lengths`): synthetic keeps the short lengths that fit the
18/60-bar demo streams (trend SMA `{2,3}×{4,5}`, MACD `2/4/3`), real uses realistic
M1 lengths (trend `{50,100}×{200,400}`, MACD `12/26/9`) so the cross is a genuine
trend signal over tens of thousands of bars, not noise. This — like the roller
sizes — is a *demo-strategy calibration* patch; the real answer is project-authored
strategies (C9: a project crate owns its own grid), deferred to the project-env
work.

**Amendment (families-comparison view, #107, 4c64feb).** The family-comparison
**view** the #104 amendment left open is now realized. `aura chart <name>`
classifies the name on disk (`TraceStore::name_kind`: a top-level `index.json` is a
single run; else member subdirs with `index.json` are a family; else not-found) and,
for a family, overlays **one tap** (default `equity`, `--tap` to pick) of **every
member** in one self-contained uPlot page: `build_comparison_chart_data` emits one
labelled series per member, all on a **single shared y-scale** — members measure one
identical quantity, so a shared scale is what makes them comparable, unlike the
single-run overlay of *different* taps (per-series scales). The series align on the
same union-ts spine via `join_on_ts`, so **one mechanism yields three correct
readings**: sweep/MC members share the data window (a true overlay), walk-forward
members are disjoint OOS windows (null-complementary → the stitched curve). The view
consumes a **set of runs** (`&[FamilyMember]` from `TraceStore::read_family`, sorted
by key for determinism, C1); a family is its *first producer* — the deliberate first
step toward the programmable analysis meta-level (C21) **without** rebuilding the
orchestration axes (that is its own later cycle). Name resolution is made a **total
function** by the write-guard `TraceStore::ensure_name_free`, called once per tracing
command (`run`/`run <bp.json>`/`run --real` → Run; `sweep`/`mc`/`walkforward` → Family)
to refuse cross-kind name reuse — so the one ambiguous on-disk state (a name used by
both a run and a family) is unreachable. Every error path exits 2, never panics
(C18/C10 refuse-don't-guess). Engine untouched (C9/C14): the whole change is
`aura-registry` (the resolver + classifier + guard) + `aura-cli` (the builder +
`emit_chart` name-kind branch + `--tap`); the single-run page is byte-unchanged when
no `--tap` is given. **Still deferred:** multi-column tap selection
(`build_comparison_chart_data` projects column 0 — the comparison taps in scope are
single-column f64; #47); and the orchestration-composability rebuild (sweep/MC/WFO as
composable meta-level tools).

**Amendment (served-page hardening — cut 2, #102 + #108, 476342d).** The two deferred
follow-ons the #107 amendment named are realized, both confined to `aura-cli` (engine
+ registry untouched, C14). **Run-context header (#102):** a `ChartMeta`
(kind/name/commit/window/broker/seed/taps, + member count for a family, + bound params
for a single run) is built from the `RunManifest` in
`build_chart_data`/`build_comparison_chart_data`, injected into
`window.AURA_TRACES.meta`, and rendered by a pure `buildHeader` in `chart-viewer.js`
(headless `.mjs`-guarded, like `buildCharts`). The family window is the **span** across
members `(min from, max to)` — the only reading that labels a disjoint walk-forward
family's true OOS coverage (it collapses to the shared window for sweep/MC).
**Decimation (#108):** a pure `decimate(ChartData, buckets) -> ChartData` min-max
transform thins the served page to ≤ ~2·`CHART_DECIMATE_BUCKETS` spine slots
(per-bucket min+max, nulls preserved), applied in `emit_chart` on both paths — a
multi-year M1 family now renders a few-thousand-point page instead of 100s of MB; full
recorded data stays on disk (view-only), and the walk-forward null-fill page collapses
for free. Deterministic (C1): pure bucketing over the sorted-deduped spine, no-op under
budget. **Refinement (#111, 2957561):** the per-bucket reduction is **tap-aware** — an
*envelope* series (equity) keeps min/max, but a *bounded level* series (the C10
bias level — pre-reframe: exposure — ∈[-1,+1]) reduces by per-bucket **mean** (a `ReduceKind` on each `Series`,
set by `reduce_for_tap`). Without it min/max made every multi-year exposure a solid
-1..+1 band (each bucket straddles many sign flips), reading as per-point oscillation;
the mean shows the net/duty-cycle level. Deferred refinements: rendering the min/max
envelope honestly as range bars / OHLC rather than a polyline (#112); a `--width`
budget flag and true intra-bucket min/max ordering for the non-default continuous
x-mode (#110).
**Refinement (2026-06-29 — the visual face is orthogonal and optional; it does not
motivate C24).** The blueprint data format (C24) is required by C21 (generation /
structural search) and C18 (reproduction of a generated run) **at the CLI level,
autonomously** — independent of any visual surface. The playground's form (web or
egui, **editor or viewer, or not built at all**) is therefore **downstream and
optional**, and topology authoring does **not** live in it. This severs an earlier
conflation that treated the playground as where topology-editing would live. C22's
"never a scene editor" is refined to its true content — **no persistent
scene-at-rest** (a World is a *program*, C21) — which does **not** forbid a future
blueprint *editor* over the World-owned topology-data (C24); should the playground
ever become one, the data format is already the substrate it round-trips, not a new
mechanism.
**Refinement (2026-07-03, #188 — visual surfaces are stateless projections; C25).**
The role-model pass generalizes the point beyond the playground: for **every**
artifact class (blueprints, op-scripts, process/campaign documents), the canonical,
complete form is **text**, every operation is executable headless, and any visual
surface — viewer or editor — is a *stateless projection* that reads/writes that same
canonical form and adds no semantics. Read-only projections (viewers, this
contract's trace explorer) rank far above write editors in value; whether an editor
is ever built is secondary, because the Blockly litmus test (C25) already
disciplines each vocabulary to be palette-generatable without one. The shipped face
is the **web-from-disk** front (revised 2026-06, #101 — not egui): disk-persisted
traces rendered as self-contained HTML chart pages.

### C23 — Graph compilation and behaviour-preserving optimisation
**Guarantee.** The bootstrap (C19) is a **compilation**: it lowers a param-generic,
named **blueprint** (the authoring source — nodes, composites, strategy, harness;
C8/C9/C20) into a flat, type-erased **`FlatGraph`** — the frozen runnable
instance (C7) — **wired by raw index, not by name** (`Edge { from, to, slot,
from_field }`). Composites are **inlined** at this step (C9): the composite
*boundary* dissolves entirely (there is no composite in the flat graph). The
blueprint's field / input-role *names* are **non-load-bearing** — the wiring
resolves by index, and names survive at most as **informative debug symbols**
(exactly as `FieldSpec.name` already is, C8), kept for tracing / rendering (C9
graph-as-data, #13) but carrying no run semantics. The flat graph is then the target of **behaviour-preserving
optimisation** — any transform that leaves every observable sink trace
bit-identical (C1 is the correctness invariant) — on two levels:
- **intra-graph** (within one graph): **common-subexpression elimination** —
  two identical nodes (same type, same bound params, same input source) merge to
  one with output fan-out, so fractal composition (C9) costs no redundant compute —
  and **dead-node elimination** — a node on no path to a sink is dropped.
  Pure-consumer sinks (C8, no output) are never CSE candidates, so their
  out-of-graph side effects are preserved by construction.
- **across the sweep family** (over the family of flat graphs one blueprint yields
  under a param sweep, C12): the sub-graph whose nodes carry **no swept param** and
  whose inputs are **all sweep-invariant** (transitively from the sources — same
  data window) is **loop-invariant** w.r.t. the sweep and is computed **once**; its
  output is materialised as a recorded stream (C11) shared read-only across the
  sweep instances (`Arc<[T]>`, C12). Only the parameter-dependent suffix re-runs
  per sweep point — loop-invariant code motion over the sweep loop.
**Forbids.** Any "optimisation" that changes an observable trace (it breaks C1);
optimising over a representation that is not graph-as-data — an opaque
trait-object interior (the rejected nested-composite reading of C9) cannot be
analysed or rewritten across its boundary, so it forecloses both levels.
**Why.** Determinism (C1) is not merely an audit property; it is the **licence**
for these rewrites — a behaviour-preserving transform is only meaningful because
"same input → bit-identical run" makes "same result" decidable, and a
sweep-invariant sub-graph is reproducible enough to compute once and share. The
flat graph representation (C19) is the necessary condition: only a flat, inspectable
graph-as-data — with each node's declared param-ranges (C8) — lets the compiler
identify identical sub-expressions, dead nodes, and the sweep-invariant frontier.
This is precisely why a composite is an inlining (C9) and not a runtime
sub-engine: the flat graph is what makes the whole graph optimisable.
**Status (Construction-layer milestone).** The flat graph *representation* —
blueprint → inline / compile → flat instance — is the load-bearing substrate built
**first**; the optimisation passes (intra-graph CSE/DCE, sweep-invariant
hoisting) are **deferred**, behaviour-preserving follow-on work, each gated by a
"flat graph with pass ≡ flat graph without pass, bit-identical run" test (C1). The
sweep-level pass further presupposes per-node param declarations (C8 — landed in
cycle 0015 as `name`+`kind`; the swept *range* still pending #32/C20) and the sweep
orchestration itself (C12/C21).
**Amendment (cycle 0032 — param-namespace injectivity is part of the compilation).**
The bootstrap-as-compilation now includes one structural gate:
`check_param_namespace_injective` over the `param_space()` name projection (see C9 /
C12-C19), run before name resolution. It reads the **boundary** name projection — the
authoring address space — and rejects a duplicated path (`DuplicateParamPath`). Node
names stay **non-load-bearing**: they qualify the param path at construction and are
dropped at lowering (the flat graph is wired by raw index, unchanged). The check makes
the by-name *authoring address space* injective; it does **not** make names
load-bearing in the flat graph.

### C24 — The blueprint is a serializable, World-owned data value (the topology data format)
**Guarantee.** A **blueprint** — the param-generic, named graph-as-data a Rust
builder produces (C9/C19) — is a **first-class serializable data value** with a
stable format, and the engine has a **load path** (data → blueprint → `FlatGraph`,
C23), not only the Rust-builder construction path. Topology is therefore a **value
the World owns** (C21): constructed, **generated**, mutated, **structurally
searched**, serialized for **reproduction** (C18), and (optionally) rendered or
edited by a visual face (C22). `model_to_json` (C9) is the **existing reverse half**
(blueprint → data, for render); this contract closes the loop. The format carries
**topology + structural axes + the param-space**, referencing nodes by their
**compiled-in type identity** — the closed, typed node vocabulary of `aura-std` + the
project `cdylib` (C8/C16) — and carries **no node logic** (computation is compiled
Rust, C17). It is **non-Turing-complete by construction** (a static DAG, no control
flow), so it structurally cannot become a second RustAst.
**Forbids.** Putting **node logic / computation** in the format (the RustAst trap —
logic is Rust, C17); a **Turing-complete or control-flow-bearing** blueprint format
(it is static data; the *generator* that emits it may be Rust, C20, but the artifact
is not a language); a **by-name node marketplace / registry** (the vocabulary is the
compiled-in closed set referenced by type identity — the format is not a distribution
mechanism, C9/C16); treating the **visual face (C22) as the motivation or the
authoring brain** (the format is required by C21/C18 at the CLI level, independent of
any UI); a **generated / searched run whose topology is not recoverable from its
manifest** (C18 reproduction); baking topology as **engine source** compiled into the
binary (the hard-wired `aura-cli` harnesses are pre-C24 scaffolding, a C16 tension,
retired as this lands). [C26, 2026-07-10 (#231): the single-price data weld inside
the surviving `wrap_r` scaffolding is retired — input roles bind archive columns
by name; the wrapper's remaining R-scaffolding retirement stays #159.]
**Why.** The World (C21) is the product, and it cannot orchestrate, **structurally
search**, or **reproduce** *families that vary topology* while topology stays opaque
Rust source baked into the engine. The **game-engine principle** (C16's engine / game
split) makes it concrete: the engine is compiled native systems; the "game" is
**content** — and topology *is* content, a data value the engine owns, serializes,
instantiates, and mutates, exactly as a game engine owns its scene / prefab /
blueprint graphs. The #109 fork was never "*who types the wiring*" — a small LLM
cannot reliably *apply* a DSL and a strong one does not need one, so a
manifest-as-authoring-surface dies on both horns (C17). It is "**is topology a
compile-time *source* artifact or a runtime, serializable, World-owned *value*?**",
and determinism (C1) + reproduction (C18) + structural search (the open search-policy
thread) force the **value**. The engine already treats topology as a runtime value
(C9 graph-as-data, C19 "cheap graph re-compilation, not a code recompile", C23 the
flat graph as the optimisation target); C24 only adds that the value **serializes out
of Rust and loads back in**.
**Status (2026-06-29; first cut shipped — cycle 0087 / #155, `d5602ec`;
construction service shipped — cycle 0088 / #157).** The
**principle** is settled (this contract, ratified in an in-context design discussion
— the #109 resolution). The **first cut now ships**: a `Composite` blueprint
serializes to a **canonical, versioned** data value (`format_version` envelope,
omit-defaults JSON) and **loads back** (data → blueprint → `FlatGraph`) via
`blueprint_to_json` / `blueprint_from_json` (`aura-engine::blueprint_serde`),
referencing nodes by **compiled-in type identity** through an **injected resolver**
whose concrete closed `match` over the `aura-std` vocabulary lives outside the engine
(`aura-std::std_vocabulary`) — the engine stays domain-free, no node registry
(invariant 9). Acceptance met: a serialized blueprint runs **bit-identical** (C1) to
its Rust-built twin. `model_to_json` (C9) remains the render half; this closes the
loop for the round-trippable vocabulary. **Cycle 0088 (#157) adds the
introspectable construction service**: a declarative, replayable by-identifier
op-script (`aura graph build` / `introspect` over a JSON op-list, the engine
`GraphSession` / `replay`) builds a runnable blueprint through validated ops — the
engine's construction gates split into *eager* per-op checks (name resolution, edge
kind-match, the double-wire arm, param bind, and acyclicity — a `connect` that would close a
cycle is rejected eagerly, #161) and *holistic* finalize checks (wiring
totality, param-namespace injectivity, root-role boundness), **both cadences calling
the same extracted predicates** (`edge_kind_check`, the shared resolution helpers,
`check_root_roles_bound` — no second validator) — plus build-free introspection over
the closed vocabulary (types, a node's ports/kinds, a partial document's unwired
slots). It **emits** the #155 blueprint; acceptance met: a graph built purely through
the ops compiles identical (C1) to its Rust-built twin, an invalid op is rejected at
the op naming the cause, introspection answers without a build. The engine `Op` stays
serde-free (the wire DTO is CLI-side); the vocabulary's enumerable companion
(`std_vocabulary_types`) lives in `aura-std` (no registry, invariant 9). **Cycle
0089 follow-up (#161 / #162, after the cycle-0088 fieldtest).** The eager acyclicity
gate above (`GraphSession::closes_cycle`, a reachability check at the closing
`connect`) closed a fieldtest-found hole where `graph build` accepted a non-DAG
op-list (invariant 5 / C9). **Lockstep:** it is a *second* home of invariant-5
alongside the bootstrap Kahn sort (`harness.rs`, `BootstrapError::Cycle`); the two
must co-evolve when the explicit delay/register node — invariant-5's sole legal
feedback — lands, or a valid delay-feedback graph the bootstrap accepts would be
rejected at construction. The holistic *finalize* faults now also read
**by-identifier** (#162): `finish()` translates the index-carrying `CompileError`s
(`UnconnectedPort` / `RoleKindMismatch` / `UnboundRootRole`) into by-identifier
`OpError` variants — still *calling* the unchanged holistic gates (the
no-second-validator lockstep preserved), only translating their result.
**Cycle 0090 (#156) codifies the forward-compat two-tier discipline.** Tier-1
(additive-optional) is serde-default silent-ignore with no `format_version` bump
(a new optional field defaults to prior behaviour, C1) — now proven by
`unknown_optional_field_is_tolerated_byte_identically` (an unknown optional key
loads byte-identically and runs bit-identically). Tier-2 (must-understand: a new
node type, edge semantics, or structural-axis kind) bumps `format_version` so an
old reader refuses cleanly (`LoadError::UnsupportedVersion` / `UnknownNodeType`,
already green). The per-section required-flag scheme is deferred (no current
Tier-2 section to validate it; recorded on #156).
Pre-ship dormancy (#61, 2026-07-10): until the first external ship there are
no out-of-repo readers — reader and writer change atomically in one commit —
so the Tier-2 bump discipline is dormant and structurally-semantic additions
(the `gangs` section) land as additive-optional fields of v1; the first ship
consciously freezes v1, gangs included, and activates the bump discipline.
**Milestone delivered — 2026-06-30, cycle 0090 — the serializable format + loader + construction service.** A green end-to-end milestone fieldtest (`fieldtests/milestone-topology-as-data/`) proves the full author → serialize → load → construct → introspect → reproduce story from the public surface alone, 0 behavioural bugs; the round-trippable format (#155), the construction service (#157), and the forward-compat two-tier discipline (#156) all shipped. Polish filed forward: op-script grammar docs + a stale example (#163), the canonical trailing-newline / `Composite` value ergonomics (#164), CLI discoverability of `build`/`introspect` (#159).
**Realization (2026-06-30, cycle 0092 — runs are built FROM blueprint-data, #165).**
`aura run <blueprint.json>` now loads a serialized **signal** blueprint
(`blueprint_from_json` → the closed `std_vocabulary`; an unknown type fails clean as
`UnknownNodeType`, the data-plane face of invariant 9), wraps it in the r-sma run
scaffolding (sinks / broker / data supplied **at run**, not serialized — C24's deferred
set), runs it, and emits a `RunReport` **bit-identical** (C1) to its Rust-built twin —
proven by `loaded_signal_runs_bit_identical_to_rust_built`. The `RunManifest` now carries
a **`topology_hash`**: SHA256 of the canonical (#164) `blueprint_to_json`, the #158
reproducibility anchor, a Tier-1 optional field (#156). The hash + helper live
research-side (`aura-cli` + `sha2`), off the frozen engine (invariant 8). This is the
**keystone of the World/C21 milestone**: topology-as-data is now *runnable*, not only
serializable. The harness wrap was made shareable — `r_sma_graph()` =
`wrap_r(sma_signal(...))`, so the Rust path and the data path are the same seam
over the same signal (a behaviour-preserving C19/C23 restructure). Scope note: the hash
covers the **signal** only (the fixed scaffolding is identified by `commit`); a content-id
distinguishing harness-structural variants is a #158/#166 concern once scaffolding varies.

**Realization (2026-07-01, cycle 0093 — the World orchestrates FAMILIES from blueprint-data,
#166).** `aura sweep <blueprint.json> --axis <name>=<csv>` loads an **open** signal blueprint,
grids the by-name axes against its `param_space()`, builds each member through cycle-1's
`wrap_r` seam, and aggregates to a `FamilyKind::Sweep` family — byte-identical in shape
to the hard-wired sweep (`append_family` / `sweep_member_reports` reused verbatim). This is the
C21 step beyond a single run: the World now constructs and orchestrates **families** of
harnesses from topology-data, not just one. Each member manifest carries the **shared**
`topology_hash` (one signal topology, only params vary; `member_key` distinguishes members) —
reproducible per C18. Two design facts: a sweep needs an **open** blueprint (a fully-bound one
has an empty `param_space`, distinct from cycle-1's bound run fixture), and the signal is
**re-loaded per member** from its serialized doc (the `Composite` is `!Clone` — its
`PrimitiveBuilder`s hold `Box<dyn Fn>` build closures, #164 — and `bootstrap_with_cells`
consumes the graph). **Monte-Carlo over a loaded blueprint shipped (cycle 0095, #170).** `aura mc
<blueprint.json> --seeds N` runs a **closed** blueprint across N seeds — each seed a distinct
synthetic price walk (`synthetic_walk_sources`, the `mc_family` `SyntheticSpec` pattern), the
draws disjoint-parallel via the engine `monte_carlo` seam (invariant 1) — and aggregates to a
`FamilyKind::MonteCarlo` family with one stored blueprint per family (the C18 hook), so it
`aura reproduce`s bit-identically (C1). MC binds no axis, so it needs a **closed** blueprint
(the sweep's open/closed distinction inverted); an open one returns a named `Err` (rendered
exit-2 at the `run_blueprint_mc` boundary, the sweep sibling's contract — no hidden exit in the
pure builder). **IS-refit walk-forward shipped (cycle 0097, #173).** `aura walkforward
<blueprint.json> --axis <name>=<csv> [--select argmax|plateau:mean|plateau:worst]` re-optimizes
the loaded blueprint's params over the user `--axis` grid (the #169 prefixed names) on each
24/12/12 IS window, selects the winner by `sqn_normalized` (the hard-wired arm's metric +
`select_winner` reused verbatim), runs it out-of-sample, and aggregates to a
`FamilyKind::WalkForward` family — persisted + content-addressed + `aura reproduce` bit-identical
(the read-side WalkForward branch rebuilds each OOS window from `manifest.window`). One
substitution deep from the hard-wired r-sma WF arm (the loaded blueprint via
`blueprint_axis_probe` replaces the built-in strategy); a bad `--axis` is a clean in-closure
exit 2, never a panic. This is Arm A (the settled direction): the loaded IS-optimizing form
honestly carries the `walkforward` name. Reduce-mode members are R-measured (`oos_r` the
meaningful summary; stitched pip-equity empty, C10). The synthetic-walk DGP
is the machinery, not trader-grade MC statistics; a real-data block-bootstrap — and the
`synthetic_walk_sources` `len:60`↔warm-up coupling it retires (a deep-lookback closed blueprint
warms poorly → silent-vacuous draws today) — ride #172. **Axis-name discovery shipped (cycle
0096, #169):** `aura sweep <blueprint.json> --list-axes` lists a loaded blueprint's open
sweepable knobs (one `<name>:<kind>` per line, `param_space()` order), then exits — the names it
prints are exactly what `--axis` binds. Every listed name is **mandatory** on a `sweep` /
`walkforward`: the blueprint must be fully bound before it runs, so a subset grid is refused with
the missing knob named (`BindError::MissingKnob`) and there is no default — pin a knob you do not
want to vary with a single-value axis (`--axis <name>=<one-value>`). A single `blueprint_axis_probe` helper now single-sources
the wrapped probe (`wrap_r(loaded_signal).param_space()`) for the sweep terminal, the MC
closed-check, AND the listing (three former inline copies → one), so **listed == swept by
construction** (and stays so across #159's harness retirement — the listing tracks whatever the
sweep actually resolves, never a second source of truth). The names are prefixed by the current
r-sma wrapping (`sma_signal.fast.length`, the nested-composite prefix), not the raw
`param_space` — which is why the discovery lives on the sweep verb (it owns the wrapping), not
`graph introspect`. CLI `--trace` is refused on all verbs (#168 for sweep/walkforward; run/mc already refused); the live trace-writer is the campaign `presentation.persist_taps` (`persist_campaign_traces`), and restoring per-member CLI traces is tracked by #224. **[Delivered 2026-07-11 (#224): `sweep`/`walkforward --trace` write per-member traces on the real-data campaign path (depth-2 fan-out, chartable by the printed family handle); only the synthetic path still refuses.]**

**Content-addressed reproduction shipped (cycle 0094, #158, C18)**: `topology_hash`
landed cycle 0092; re-deriving a member's FlatGraph from a stored manifest + the
content-addressed blueprint store (`aura reproduce`) shipped cycle 0094 (see C18
Realization). What **remains** is a content-id that covers **structural-axis / whole-harness
variants** (the scaffolding is not yet blueprint-data); the debug-name-in-id question is
settled by cycle 0104's **identity id** (#171: `blueprint_identity_json` + `graph
introspect --identity-id`, an additive sibling — the byte-exact content id keeps the
store/reproduce roles; introspection-only until a dedup consumer exists). Still deferred: retiring the pre-C24
hard-wired `aura-cli` harnesses (`HarnessKind`, `run_r_sma`, `*_sweep_family`) once
the project-as-crate layer lands (#159, paired with #157's data-authoring surface). **Out of the first cut's round-trippable set**
(deliberate; fails clean as `UnknownNodeType`, never a silent wrong graph): recording
sinks (capture an `mpsc::Sender` — runtime identity, not param-generic data, C19) and
construction-arg builders (`LinComb` / `CostSum` / `SimBroker` / `Session` —
structural-axis args, a C20 concern), additively addable later (#156). The
**project-as-crate load boundary landed in cycle 0102** (`Aura.toml` discovery +
`cdylib` loading + merged project ∪ std vocabulary — see the C13 realization
note; the `aura new` scaffolder followed in cycle 0103 — one command emits a
buildable project whose blueprint runs through the merged vocabulary); of the
two layers this paragraph used to name as sequencing-coupled, what remains
open is the **composable-orchestration** thread (#109): topology-as-data is
the substrate it stands on. **Canonical project shape (#181, resolved
2026-07-02):** the `aura new` templates (`scaffold.rs`) are the canonical
authoring shape and evolve with the engine; the cycle-0102 `demo-project`
fixture is an intentionally frozen known-good twin for the load-boundary
tests. The two are deliberately **not** lockstep-guarded: no consumer requires
them to match, each is e2e-guarded on its fitness for purpose (build →
descriptor load → charter check → deterministic run — blueprint *wiring*
content is pinned in neither, stated honestly), and an equality guard would
convert every deliberate template improvement into forced churn of the frozen
fixture — the same cross-purpose coupling that rules out regenerating the
fixture from the scaffolder.

**Op-script grammar (`aura graph build`, the #157 wire surface).** The construction
op-script is a JSON **array of ops**, each object internally tagged by `"op"`,
replayed in order; nodes are referenced **by identifier**, ports as dotted
`<identifier>.<port>`. The eight verbs:
- `source` — `{"op":"source","role":<str>,"kind":<ScalarKind>}` — declare a root
  source role producing a base column of `kind`.
- `input` — `{"op":"input","role":<str>}` — declare a root input role (kind inferred
  from the slots it feeds).
- `add` — `{"op":"add","type":<TypeId>,"name":<str>?,"bind":{<param>:<Scalar>}?}` —
  add a node of compiled-in type identity `type`; **`name` is its identifier**
  (mirrors the builder's `.named(...)`; defaults to the lowercased type label, so
  two unnamed nodes of one type collide); `bind` sets params.
- `feed` — `{"op":"feed","role":<str>,"into":[<port>,…]}` — fan a root role into
  interior input slots.
- `connect` — `{"op":"connect","from":<port>,"to":<port>}` — wire an interior output
  field to an input slot; a `connect` closing a cycle is rejected eagerly
  (invariant 5).
- `expose` — `{"op":"expose","from":<port>,"as":<str>}` — promote an interior output
  field to a boundary output, aliased by `as` (a real alias, not a naming; contrast
  `add`'s `name`) — one of the two verbs that keep `as` (with `tap`).
- `tap` — `{"op":"tap","from":<port>,"as":<str>}` — declare a measurement **tap** on
  an interior output field under `as` (#284) — the output-side twin of `expose`: a
  recorded observation point (a `Composite.taps` entry, C27), not a boundary output.
  Name-addressed like every other op (no raw index); tap names are their own
  namespace (a duplicate refuses). The `finish` gate threads op-declared taps into
  the built `Composite` (`.with_taps`); a single `aura run` records each, a sweep
  leaves them inert.
- `gang` — `{"op":"gang","as":"channel_length","into":["channel_hi.length","channel_lo.length"]}`
  — fuse two or more sibling params into ONE public knob: the member addresses
  leave the sweepable param space and `as` replaces them; the bound or swept
  value fans out to every member at bootstrap. Members must share one scalar
  kind and stay open (un-bound).

Value forms are the #155 representations: a `Scalar` bind value is the typed tag form
`{"I64":2}` / `{"F64":0.5}` / `{"Bool":true}` / `{"Timestamp":<i64>}`, and `kind` is
the capitalized `ScalarKind` (`"F64"`). Worked example:
`fieldtests/cycle-0088-construction-op-script/c0088_1_sma_crossover.json`
(an SMA-crossover bias). The surface is introspectable build-free:
`aura graph introspect --vocabulary | --node <T> | --unwired`. (Surfacing this same
grammar in `aura graph build --help` rides with the CLI-discoverability work, #159.)

**Canonical form (#164).** The canonical blueprint artifact is exactly the bytes
`blueprint_to_json` returns — a JSON value with **no trailing newline**.
`aura graph build` emits those bytes verbatim (it does not frame them with a display
newline via `println!`), so the CLI and library emit paths are **byte-identical** — a
prerequisite for content-addressed topology identity (#158, a hash over the canonical
form). The **canonical JSON is also the blueprint's equality / identity surface**:
`Composite` / `PrimitiveBuilder` deliberately carry **no in-memory `PartialEq` /
`Debug`** (the recipe holds a `build: Box<dyn Fn>` closure — non-comparable,
non-printable; equality could only be defined over the serialized *data*, of which
`blueprint_to_json` is already the single source — a second in-memory notion would be
a drift hazard against the very form #158 content-addresses). The loader stays lenient
(a trailing newline on input still parses, Tier-1 robustness).

**Enforcement shift — invariant 9 on the data plane (2026-06-30, cycle-0091 analysis,
adversarially verified).** Lifting topology onto the data plane relocates *where* the
engine/project boundary (invariant 9, no bespoke node registry/marketplace) is enforced,
without changing what it forbids. **Pre-C24** a blueprint referencing another project's
node was a **compile error** — topology was in-process Rust, so cross-boundary node
resolution was *structurally impossible*, compiler-guaranteed for free. **Post-C24** that
same reference is a **type-id string in a serialized blueprint**, refused only by the
injected resolver's closed set (`UnknownNodeType`). The anti-NIH rationale survives intact
(node *logic* stays cargo+Gitea-only; the format distributes **topology-as-content**, never
logic — C17), and `std_vocabulary` stays a compiled-in dispatch table, not a registry — but
its enforcement **degrades from compiler-guaranteed to resolver-seam discipline**. Two
consequences: (1) **#160** (the guard that the closed vocabulary stays honest) is no longer
droppable hygiene — it guards the data-plane face of the boundary (its own drift direction
still fails *safe*, `UnknownNodeType`). **Delivered cycle 0105:** the
`std_vocabulary_roster!` macro expands the resolver match and the enumerable
`std_vocabulary_types()` list from one roster, closing the resolver-vs-list drift mode by
construction; the residual (a new zero-arg node never rostered at all) stays fail-safe,
guarded by the one-line maintainer surface plus the count pins (the in-crate shape test and
aura-cli's cross-boundary `--vocabulary` count e2e). (2) The **injected per-project resolver** (C16) is
the genuinely new, *deferred* invariant-9 surface: nothing structurally stops a project
resolver from accepting arbitrary type-ids, or a project from layering a blueprint
*marketplace* (store + type-discovery API) **on top of** the format — one layer *above* the
engine contract. Invariant 9 holds **at the engine**; the project/ecosystem boundary (what
an injected resolver may resolve, where closed-set discipline draws the line) is a
**World/C21-layer charter point**, not an engine fix. Invariant 8 (frozen) is likewise
reframed by C24/C21: from "topology baked at build time" to "the World may *generate*
topology at runtime (research plane), the chosen blueprint is frozen into the deploy
artifact, and any run is deterministic once instantiated" (C1).

### C25 — The role model: nine authoring roles, cut by artifact + surface + iteration cost
**Guarantee.** aura's user-facing design is organized by **roles**, cut by the
artifact a role owns, the surface/language it works in, and the iteration cost it
tolerates — never by org chart. One trader — or an LLM actor, which is the point of
the whole authoring design — must be able to fill *every* role; the separation
separates *surfaces with different iteration costs and failure modes*, not people,
and switching roles is a visible act. The nine roles (ratified 2026-07-03, #188):
**1 system programmer** (the engine; Rust, this repo; all invariants),
**2 extension dev** (native nodes + analysis blocks; Rust in project/shared crates;
C7/C8, determinism in `eval`), **3 toolchain dev** (playground/viewer/skills
pipeline; vendor-side; authoring ergonomics), **4 data curator** (recorded streams,
sidecars, derived/news recordings; CLI + recording edge; C2/C3/C6),
**5 methodology designer** (validation/eval **process documents** — "the game
rules"; closed data vocabulary; anti-false-discovery), **6a strategy designer**
(blueprint topologies; data — op-script/blueprint JSON, the graph idiom; C5/C7),
**6b campaign designer** (**campaign documents** — persisted experiment intent;
data, the pipeline/block idiom; C1), **7 player** (owns nothing — explores traces,
tunes runtime params; the playground, C22/C12; read-only by design), and
**8 operator/auditor** (frozen bots, reconciliation, money management; deploy-edge
CLI, manifests, reproduce; C13). The 6a/6b split follows invariant 12's tier
boundary (node/harness vs World); the interface between them is the id machinery
(content id = byte-exact, identity id = topological). Param gradient: 6a defines
topology + open params, 6b spans spaces over them, 7 moves inside those spaces
live. A role is **recognizable** when four things exist: a named artifact type it
owns, a surface addressed to it, an entry path, and its invariants enforced at its
boundary. **Text-first / headless-first is an invariant, not a taste** (user,
2026-07-03: editors must never be the only way; LLM operability demands it): every
artifact class has a canonical, complete, text-serialized form; every operation is
executable headless via CLI/API; visual surfaces are *stateless projections* that
read/write the same canonical form and add no semantics — read-only projections
(viewers) rank far above write editors. The **Blockly litmus test** is the
acceptance criterion for every artifact vocabulary, editor or no editor: a block
palette must be *generatable* from the vocabulary — every block with typed slots,
every valid composition snappable, every invalid one not.
**Forbids.** An artifact class whose only authoring path is a visual editor or a
Rust compile cycle when the role's iteration cost demands data (the role-6b
lesson: a tiny campaign change must never cost a compile); stringly-typed fields,
implicit inter-block coupling, or "arbitrary JSON here" holes in a role's
vocabulary (they fail the litmus test); collapsing the 6a/6b idioms into one
surface (dataflow boxes-and-wires vs sequential pipeline blocks are different
languages).
**Why.** The game-engine analogy that seeded aura (C16) extends to its people:
engines separate system programmers, toolchain devs, asset creators, level
designers, and players because their artifacts, tools, and iteration loops
differ — a design that forces one role's technique on another (Rust for campaign
tweaks, an editor as the only entry) mis-prices iteration exactly where research
throughput lives. Realization: cycle 0106 (#189) shipped roles 5/6b their
artifacts (process/campaign documents, C18 realization note); roles 4/7/8 remain
technically present but faceless (no addressed verb families yet); role homes in
the project layout and docs-by-role are open (#192 context).

### C26 — Harness input binding: role names bind archive columns
**Guarantee.** A strategy blueprint declares WHICH data it consumes as the NAMES
of its root input roles: a role whose name is in the **closed column
vocabulary** — `open`, `high`, `low`, `close`, `spread`, `volume`, plus `price`
as the backward-compatible alias of `close` — binds by default to that column of
the campaign cell's (or run invocation's) instrument. A campaign document may
**override** the name default per role via the additive `data.bindings` block
(`role name → column name`; serde `default` + skip-if-empty, so binding-less
documents keep their content ids) — the 6b rebind seam: the blueprint's content
identity never changes. Resolution (`aura-cli`'s `binding` module,
`resolve_binding`) produces ONE ordered plan consumed by BOTH halves of the old
weld: the columns are opened (`aura_ingest::open_columns`, the generalization of
`open_ohlc`/#92) and the wrapped root roles declared (`wrap_r`) in the **same
canonical order** — `M1Field` declaration order (open, high, low, close, spread,
volume), filtered to the consumed set — which is the C4 merge tie-break order,
so role i receives source i by construction. A close column is always part of
the plan (shared when the strategy consumes `close`/`price`, else opened for the
broker/executor pair alone). The vocabulary is **Blockly-litmus-clean** (C25):
role-name slots draw from a closed enum, the bindings block is typed
`role → column` with no free-form holes, and validation is two-tier — values
against the column vocabulary in the intrinsic tier (`validate_campaign`), keys
against the strategies' `input_roles()` in the resolver tier
(`validate_campaign_refs`).
**Forbids.** Guessing a column for an unknown role name (refuse with the
vocabulary + the override remedy, never default); opening columns in any order
other than the canonical declaration order (the C4 tie-break contract);
free-form or logic-bearing binding values (the C17/C25 line — a binding value is
a typed column reference, nothing else); fabricating synthetic OHLC when a
multi-column strategy meets synthetic data (the walk generates a close series
only — refuse with the `--real` remedy).
**Extension point.** When recorded non-price sources land (the #71 Source seam),
the binding VALUE-space grows additively from archive columns to recorded-stream
references — a root role like `sentiment` becomes bindable to a recorded stream
then, and until then refuses with the vocabulary-naming message. The role-name
key-space and the campaign `bindings` carrier are unchanged by that growth.
**Why.** The single-price weld (`wrap_r`'s hard-wired `price`←close and the six
`M1Field::Close`-only open sites) made every strategy monocular regardless of
what its blueprint declared; binding by role name keeps the blueprint the single
source of its own data needs (C24: topology-as-data carries its input contract),
lets a campaign re-aim a strategy without touching its content id (C18
identity), and pins opening and declaring to one shared, canonically-ordered
plan so the two halves cannot drift (C1/C4 determinism).

---

### C27 — Declared taps: named measurement points bind sinks run-mode-aware
**Guarantee.** A blueprint may declare **taps** — named, pure output-side
declarations `{ name, from: {node, field} }`, the output-side twin of
`input_roles` (C26). A tap names an interior producer's output field without
naming a sink, exactly as a `Role` names an abstract input without naming a
source. At compile the tap resolves — and, for an interior composite, **hoists**
to the root — through the same lowering remap edges and `OutField` re-exports
use (`resolve_tap_wire`, a `flat_taps` accumulator threaded through the lowering
recursion), landing in `FlatGraph.taps` as a `FlatTap { name, node, field }`
whose name survives compile and is load-bearing for by-name binding (like
`SourceSpec.role`, #275). Binding is run-mode-aware: the run-mode-owning layer
constructs a sink (a `Recorder`) at a bound tap via `FlatGraph::bind_tap`, which
takes a **caller-built** `Box<dyn Node>` sink (so the engine keeps its
`aura-core`-only production dependency — it never constructs a domain sink type)
and appends it plus an edge before bootstrap. The single-run path (`run_signal_r`)
binds and records each declared tap, persisting the series through the existing
trace store (`env.trace_store()`), so the tap columns surface through the same
tooling the campaign path feeds; a sweep/reduce run leaves taps unbound.
**Forbids.** A tap carrying a channel endpoint or effect in the serialized
artefact — recording policy is run-mode authority, not fragment-embedded (a
fragment must not drag its measurement decisions into every harness that embeds
it; the tier ontology, C20/C21). The engine constructing a domain sink type
(the `aura-core`-only wall — the sink is caller-built). Order statistics
(median, etc.) inside the graph — they stay sink/analysis-side (C18);
multi-instrument study inputs stay harness/World tier.
**Non-error.** An **unbound** tap is inert, not a fault — unlike an unbound root
input role, which `check_root_roles_bound` rejects (C26): observation is optional,
a fed input is mandatory. A declared-but-unbound tap compiles and runs, its
producer evaluating and its output discarded (a no-out-edge producer is a valid
runnable sink — the Kahn sort emits it, `check_ports_connected` gates only inputs).
**Why.** Observability must be expressible in a hand-authored blueprint — the
measurement-shaped study computes in the graph and surfaces via taps, no
throwaway Rust harness — while recording stays a run-mode decision, not a
fragment-embedded effect. Taps are designed **DCE-compatible** (a bound tap is a
natural DCE root, an unbound tap a dead declaration) but this contract does
**not** depend on DCE: an unbound tap's sink is simply never constructed
(build-time elision, which the engine already tolerates). The chain-pruning
benefit — a sweep paying zero for the study wires behind an unbound tap — is
**deferred to the future DCE cycle** (C23); the mechanism ships now, verified
sound. (#282, 2026-07-18.)

### C28 — Internal stratification: the trading ladder, the process column, the shell
**Guarantee.** The aura workspace's crates realize a layered responsibility
model along two axes. A **ladder**, ordered by domain specificity from inner to
outer:
1. **engine** — the domain-free deterministic streaming runtime and vocabulary
   (cells/kinds/freshness/firing, graph build, compile, run, taps/trace — C1–C9,
   C19, C23, C24), the domain-free node roster (arithmetic/logic/rolling nodes
   plus the generic `Recorder`/`GatedRecorder`/`SeriesReducer` sinks), and
   generic statistics (the Monte-Carlo and moving-block-bootstrap kernels). The
   layer name is wider than the crate `aura-engine`: it spans `aura-core`,
   `aura-engine`, the domain-free part of `aura-std`, and the generic-statistics
   surface.
2. **market** — what a market *is*, carrying no analysis or strategy intent:
   instruments and pip/point geometry (C15), session anchoring, bar resampling,
   market-data ingestion (`aura-ingest`).
3. **measurement** — descriptive statistics over market streams (session
   statistics, conditional rates, distributions). Sibling of **strategy**: both
   consume *market*, neither imports the other.
4. **strategy** — the *definition* of trading signals: bias, stop rules, sizing,
   cost-model nodes.
5. **backtest** — the *evaluation* of strategies: simulated execution without
   money (the `SimBroker`, position-management), the R-metric reductions and the
   position-event table, and the per-run scaffold. Backtest mirrors *execution*
   on the research side — execution semantics in R units, money exiled.
6. **execution** — money, account-term sizing, the live broker; already exiled to
   the deploy edge by C10/C13, existing today only as that ratified boundary.

Beside the ladder stands the **process column** — the research-process machinery
(the run registry C18, the process/campaign document types, campaign execution).
It consumes run *artifacts*, not market streams, and orchestrates runs of any
ladder layer; it stands beside the ladder, not on a rung. The **shell** (the
`aura` CLI) imports everything and is imported by nothing.

**Import rule.** An outer ladder layer may import inner layers, never the
reverse; *measurement* and *strategy* are siblings (no import either way);
*backtest* may import *strategy*. The process column imports the engine layer
plus the run-artifact and metric interfaces, and is imported by no ladder crate;
column-internal edges are free. The shell imports all; nothing imports the
shell. **`dev-dependencies` are exempt** — tests may cross layers (the existing
`engine`/`ingest`/`registry` → `std` edges are dev-only and stay). The rule
binds **crate structure, not graph composition**: a blueprint may feed a
measurement statistic into a bias input — data flow inside a graph is free (C24);
layers govern imports, graphs compose freely.

**Forbids.** An inner layer importing an outer one — most sharply the engine
layer importing backtest reductions, or market importing strategy. A ladder crate
importing the process column. Money (currency P&L, account sizing) inside the
strategy or backtest layers (C10/C13 — it lives only at the execution/deploy
edge). Once a second consumer warrants the split, keeping multiple layers welded
in one crate's roster.

**Why.** The stack is a framework specialized for traders: the inner engine is a
domain-free analysis substrate (the same machinery would measure robot telemetry
or any timestamped process), the outer rungs the trading specialization, and the
two together are the "game engine for traders" (C16's game/engine split applied
*inside* the workspace, from the engine|project boundary to the intra-stack
layering). Separable responsibilities behind narrow, contract-defined seams let a
contributor focus on one rung without absorbing the rest, and make each boundary
auditable. Enforcement is the crate graph itself: once crates are cut along these
cells, a layer violation is a compile error and every new edge a visible
`Cargo.toml` diff — no linter, no discipline appeals. Five of the six seams are
already ratified contracts and this model only *names* them as layer boundaries:
the node contract (C8, engine ↔ any vocabulary), blueprint-as-data (C24,
topology ↔ engine — its shape selecting the run scaffold is the additive #286
refinement, phase 3 below), declared taps (C27, run ↔ analysis — the only way
values leave a run), the run registry (C18, run ↔ process column), and the
deploy edge (C10/C13, everything ↔ money). Only the
process column ↔ metric interface is new (a named metric vocabulary *supplied* by
measurement and backtest instead of baked in R-only — this is #147).

**Status (2026-07-19, milestone "Stratification — ladder, process column,
shell", #286).** This contract states the *target*. At HEAD the crates cut by
mechanical role (vocabulary / reductions / documents / orchestration / CLI), not
cleanly by layer, so the layering is realized only partially:
- The dependency *direction* now obeys the rule across the engine stack. The
  `aura-engine → aura-backtest` production violation is cut (phase 2, #292):
  `RunReport` is generic over its metric payload `M` (the engine names no
  concrete metric type), the pip/R reductions and the MC assembly (`summarize`,
  `McAggregate`/`RBootstrap`/`monte_carlo`) moved to `aura-backtest`, and the
  statistics kernel (`MetricStats`/`quantile`/`resample_block`/`SplitMix64`)
  moved to the `aura-analysis` foundation. The engine's `[dependencies]` are now
  `aura-core` + `aura-analysis` only; the backtest layer instantiates
  `M = RunMetrics` (`aura-backtest → aura-engine`, an outer→inner edge). The
  ladder direction is enforced for the engine/backtest/analysis rungs by the
  structural test (`c28_layering`, seven-row table).
- **#147 retired (user-ratified direction 2026-07-20; shipped the same day).**
  Item 1 — the metric genericity `RunReport<M>` — shipped as phase 2 above
  (#292). Item 2 — the registry deflation vocabulary — shipped as the ratified
  "A1" cut, its deferral trigger having fired when measurement supplied its
  first deflatable metric (the IC, #290): the deliberately narrow
  `MetricVocabulary` trait (resolve/roster/direction/value/one null draw)
  lives in `aura-analysis`, re-exported through `aura-engine`; the R
  vocabulary (`RunMetricKey`, `r_based`, the rosters, the centred
  moving-block `null_draw`) is supplied by `aura-backtest`; the registry's
  rank/optimize/deflate machinery is generic over `M: MetricVocabulary` with
  refusal prose derived from the carried roster; the IC (`aura-cli`) is the
  second production implementor, bringing its within-run permutation null.
  The C10 wall stays monomorphic (`check_r_metric`/`generalization` accept
  only the R vocabulary; `r_based` is the enforcement point). Explicitly
  still deferred ("A2"): measurement runs as sweep-family citizens (report
  unification, campaign engine generic-over-M) — until a concrete
  family/campaign demand exists. The #136 one-implementor rationale is
  superseded by the second implementor; the registry's process-column
  trading-awareness holds unchanged. See #147 for the full disposition.
- The `aura-std` four-layer roster is now cut by layer (phase 4, #288): `aura-std`
  holds the engine nodes only (arithmetic/logic/rolling + the generic sinks);
  `aura-market` (`session`, `resample`), `aura-strategy` (`bias`/`stop_rule`/
  `sizer` + the cost nodes) and `aura-backtest` (`sim_broker`,
  `position_management`) carry the outer rungs, each depending only on `aura-core`;
  the closed node roster moved to `aura-vocabulary`. The `aura-analysis`
  interweave is resolved (phase 5, #291): the backtest reductions live in
  `aura-backtest::metrics` beside their `position_management` producer, and
  `aura-analysis` is reduced to domain-free statistics + selection provenance
  (`[dependencies]` = serde only). No crate exists yet for *measurement* (its run
  verb is the additive shape dispatch, #286) or *execution* (unbuilt — the C10/C13
  edge only). Under this model the `aura-registry → aura-research` edge is
  column-internal and legal.
- Phased realization (each independently shippable; behaviour byte-identical
  except the purely additive shape dispatch): (1) this contract; (2) cut the
  engine's backtest-metrics edge via `RunReport<M>` — **done** (#292:
  metric-generic run record, the pip/R reductions + MC assembly relocated to
  `aura-backtest`, the statistics kernel to `aura-analysis`, dependency
  inversion, ladder enforced by the structural test; realizes item 1 of #147);
  (3) the #286
  shape dispatch plus the per-run scaffold as a library (seeds an `aura-backtest`
  crate, gives *measurement* its run verb, removes the measured O(cycles) run-time
  retention); (4) split the `aura-std` roster along engine / market / strategy /
  backtest — **done** (#288: four `aura-core`-only node crates, the closed roster
  moved to `aura-vocabulary`, the ladder direction enforced by a structural test);
  (5) split `aura-analysis` into generic statistics and backtest metrics —
  **done** (#291: metrics moved to `aura-backtest::metrics`, `aura-analysis`
  reduced to the domain-free half, engine re-export surface name-unchanged); (6)
  generify the column's metric interface (demand-driven — this is #147). Crate
  names now realized (`aura-market`/`aura-strategy`/`aura-backtest`/
  `aura-vocabulary`); full evidence on #288, #286 and the milestone.

---

## Open architectural threads not yet resolved

- **Playground & World UI surface** — the playground is core (C22); the surface
  is a **web frontend served from disk-persisted traces** (revised 2026-06, issue
  #101; not egui). Settled for the first cut: raw per-tap trace persistence to
  disk (columnar/SoA form, C7) + serve-time `join_on_ts` alignment + a static
  self-contained HTML chart page (uPlot, vendored like the `render_html`
  Graphviz-WASM blob), feeds overlaid or timestamp-aligned in panels. The
  families-comparison **view** — `aura chart <family>` overlaying one tap across a
  family's members on a shared y-scale — shipped (#107, see the C22 amendment).
  Still open: richer comparison meta-views (sweep-surface heatmaps, cross-family /
  multi-strategy comparison, multi-column tap selection #47), a local server, and the
  run/replay clock controls.
- **Parameter-space search strategies** (Bayesian/genetic) — pluggable policies
  atop the atomic sim unit (C12), not yet designed. Search over *params* sits atop the
  atomic unit; search over *structure* (graph mutation / crossover — NEAT-style)
  additionally needs topology-as-data (C24).
- **`aura new` scaffolder and the experiment-builder API** — `aura new`
  scaffolds a Rust project *crate* (node / strategy blueprints) against the
  engine (C16/C20); the experiment-builder API surface (harness wiring,
  structural axes, sweep combinators) is not yet designed. `Aura.toml`'s
  schema was settled paths-only in cycle 0102 (data archive root, runs dir —
  see the C13 realization note); the load boundary itself shipped there.
- **The analysis meta-level — composable orchestration + project-as-crate authoring
  (tracked: #109).** aura's differentiator (C21) had two unbuilt halves: (1) the
  orchestration axes (sweep / Monte-Carlo / walk-forward) becoming *composable tools*
  a user wires into an analysis workflow, rather than today's hard-wired CLI verbs
  (`sweep_family` / `walkforward_family` in `aura-cli`) — still open; and (2) the
  project-as-crate authoring layer above — its **load boundary landed in cycle 0102**
  (`Aura.toml` discovery + cdylib loading + merged vocabulary, C13 realization note)
  and the **`aura new` scaffolder in cycle 0103**; of that layer only the
  experiment-builder API remains open (C16/C17).
  On the meta-level, authoring a strategy is *wiring
  existing nodes* (C9 composition) + *defining the analysis framework* (C21), not
  writing new nodes; the user wants it driven via the CLI, later the interactive
  server / playground (C14/C22). **Resolved (2026-06-29) → C24.** The fork was
  mis-posed as "(a) run-a-Rust-experiment-via-CLI vs (b) wire-nodes-via-CLI". The real
  axis is **topology = compile-time Rust source vs runtime, serializable, World-owned
  data value**, settled as the **value** (C24, the game-engine principle): node
  *logic* stays Rust (C17), *topology* becomes data the World generates / serializes /
  reproduces. "Wire-nodes-via-CLI" is dropped — interactive wiring through the CLI is a
  non-goal; it collapses to a file + parser, which *is* C24's load path. What
  **remains** under #109: the **blueprint data format** itself (C24 Status — its own
  brainstorm / milestone), and the **composable-orchestration** half — the axes
  (sweep / MC / walk-forward) becoming tools applied to a World-constructed harness
  instead of the hard-wired `aura-cli` verbs (`sweep_family` / `walkforward_family`).
  **Status (cycle 0106, #189 — the artifact half shipped v1).** The #188 role-model pass
  re-cut the "experiment-builder API" reading of this thread (role-6b work mis-typed in
  role-2 technique): experiment intent is now **data**, not a Rust API. Cycle 0106 shipped
  both document vocabularies (process document, campaign document — `aura-research`),
  two-tier validation, the op-script-precedent introspection contract
  (`aura process|campaign introspect --vocabulary/--block/--unwired/--content-id`), and
  content-addressed stores (C18 realization note) — authorable and checkable headless, no
  compile, no run. **Status update (cycles 0107–0110).** The executor question resolved and
  shipped (cycles 0107/0108, #198/#200: `aura-campaign` executes the v2 pipeline shape over
  the `MemberRunner` seam); the #188 amendment package landed 2026-07-03 (C25 role-model
  entry, C20/C22 refinements, invariant-10 clarification). The "once it carries" dissolution
  of the hard-wired verbs (user decision 2026-07-03 on #188) is **running as the milestone
  "Verb dissolution" (#210)**: the fork triage of 2026-07-04 decided its design (dissolve
  the real-data blueprint branches only, built-in/synthetic branches stay verb-wired until
  #159; generated documents auto-registered; full behaviour parity modulo the recorded
  additive instrument stamp), and the verb set dissolved in the #210-decision-7 order: cycle 0110 took `aura sweep
  <bp.json> --real …` (enabled by the `std::sweep` selection group becoming optional —
  all-or-nothing, selection-free = terminal-stage-only; wire form and every stored content
  id unchanged), then generalize, walkforward, and mc's R-bootstrap path, each now sugar over
  a generated, content-addressed campaign document through the one executor, plus a structural
  risk-regime axis (`CampaignDoc.risk: [RiskRegime]`, sole `vol{length,k}` variant — the stop
  compared as a matrix dimension, stamped into every member manifest, never argmax-swept).
  Ad-hoc verb intent no longer evaporates into shell history — the #188 diagnosis's cure
  applied to the verbs themselves. **The dissolved form is per-verb, by intended scope**
  (ratified at milestone close, fieldtest 2026-07-07): for sweep it is the blueprint file
  (`<bp.json> --real`), while `aura sweep --strategy r-sma --real` stays the inline built-in
  path (its member lines carry no instrument/topology_hash/selection stamp and register no
  campaign document) — the built-in `--strategy` demo surface is #159's hard-wired-harness
  retirement target, not the dissolution's; for generalize/walkforward/mc the dissolved
  form is now the same generic grammar as sweep — an arbitrary blueprint positional plus
  `--real` and repeatable `--axis <wrapped-name>=<csv>` (#220). [HISTORY — superseded in
  two steps. #159 (cuts 1b-4, post-2026-07-07) retired the built-in `--strategy`
  sweep/demo surface: the inline `aura sweep --strategy r-sma --real` path no longer
  exists. #220 then removed the verbs' weld — at milestone close the dissolved form of
  generalize/walkforward/mc was still the welded `--strategy r-sma --real`; #220 made
  the three verbs blueprint-generic (arbitrary blueprint + arbitrary `--axis`; mc keeps
  the synthetic `--seeds` family unchanged beside the new `--real --axis` campaign mode;
  generalize takes `--real <SYM1,SYM2,…>`, >=2, with one value per axis), deleted the
  welded `--strategy` grammar (clap rejects it, exit 2), dissolved `RGrid`, and unified
  the verbs on the #214 invocation struct. The surviving form everywhere is `aura <verb>
  <blueprint.json> --real … --axis …` over examples/r_*.json.] Milestone closed 2026-07-07 on a green end-to-end fieldtest
  (0 bugs; behaviour preservation, campaign-substrate reach-through, and the risk-regime axis
  all confirmed); residual findings are discoverability/ergonomics follow-ups (#216 risk-axis
  discoverability, #217 verb knob asymmetry, #218 no-project store litter).
  **Amendment (2026-07-14, #256 fork B):** the dissolved walkforward/mc
  translations' leading sweep became the enumerate-only **`std::grid`** stage —
  a fieldless vocabulary block, legal only as the first stage and immediately
  before `std::walk_forward`. Only the grid's parameter points ever crossed the
  stage seam (the wf stage re-sweeps them per IS window itself), so the leading
  stage no longer executes members or persists a `Sweep` registry family:
  persisted dissolved-walkforward/mc campaign documents lose that family, while
  the visible grades are byte-identical (the exact-grade E2E pins are
  unchanged). The executor's inter-stage seam is now a typed two-armed flow
  (points-only vs executed members); report-consuming stages are fenced by
  preflight. `translate_generalize` keeps its executed `std::sweep(argmax)`
  leading stage — its generalize stage consumes the argmax winner report as the
  cell nominee.
- **Inferential honesty of the World — family-selection without false-discovery
  control (tracked: milestone "Inferential validation (defend against false
  discovery at sweep scale)", #144 / #145 / #146; adjacent #139).** The World's
  massively-parallel sweep (C12 axes 1–2, C21) is aura's differentiator *and* its
  most direct route to false discovery: `optimize` / `rank_by` select the single
  best family member by a bare argmax, with no penalty for the number of
  configurations tried, no preference for a robust parameter neighbourhood over a
  sharp in-sample peak, and no cross-instrument generalization read; `mc` is a
  descriptive seed-sweep, not an inferential significance test. The hygiene
  invariants keep one backtest honest (C1 determinism, C2 no look-ahead); they do
  **not** make a *selection across a family* honest. Recognized direction: the
  selection/aggregation layer must deflate a winner for the family size (#144),
  prefer a plateau over a peak (#145), and score cross-instrument generalization
  (#146), with a per-candidate out-of-sample bootstrap as the adjacent
  significance read (#139, landed cycle 0075). Distinct from the two threads above —
  neither orchestration *composability* (#109) nor a search *policy* (Bayesian/
  genetic), but the statistical *validity* of the selection itself. Not a
  C-invariant until built; recorded as the World's third half — **now structurally
  complete** (all three pieces built, cycle 0078).
  **Status (cycle 0076):** the trials-deflation piece (#144) landed —
  `optimize_deflated` (aura-registry) wraps `optimize` and records, additively on
  the winning member's manifest (C18, the new `RunManifest.selection`), a deflated
  score + an overfit probability for the family size, **without changing which
  member wins** (C23; `optimize` / `rank_by` stay a bare argmax — the deflation is
  recorded provenance, not a re-ranking). The R arm is a centred moving-block
  reality-check (reusing the `r_bootstrap` kernel); the `total_pips` arm a
  closed-form expected-max-of-K dispersion floor. **Status (cycle 0077):** the
  plateau-over-peak piece (#145) landed — `optimize_plateau` (aura-registry)
  argmaxes the **neighbourhood-smoothed** metric surface (mean or worst-case over
  each member's closed mixed-radix grid neighbourhood) instead of the bare peak,
  recorded on the same `RunManifest.selection` carrier, now an orthogonal *rule ×
  annotation*: `SelectionMode::{Argmax, PlateauMean, PlateauWorst}` with either the
  deflation annotation (#144) or the plateau annotation (`neighbourhood_score` /
  `n_neighbours`). It is opt-in via a `--select` flag — default argmax stays
  byte-identical (C23). The grid lattice surfaces from the engine
  (`SweepBinder::sweep_with_lattice`); the policy stays in aura-registry with
  `walk_forward` selection-agnostic (C9). Selection is now a *pluggable objective*
  (bare argmax → trials-deflated → plateau), not a single hard-wired argmax.
  **Status (cycle 0078):** the last piece — cross-instrument generalization (#146) —
  landed, completing the inferential half. Unlike #144/#145 (which *select + annotate*
  a within-family winner on `RunManifest.selection`), #146 is an **aggregator/
  validator**, not a selector: the `aura generalize` subcommand runs a *brought*
  candidate across an instrument list and `generalization` (aura-registry) reduces the
  per-instrument R-metrics to a **worst-case floor** (min over instruments — the
  cross-instrument sibling of `PlateauMode::Worst`, R-only per C10) + a sign-agreement
  count + the per-instrument breakdown. It is a *recomputable aggregate* over a new
  `FamilyKind::CrossInstrument` family (C12's comparison axis, realized), each member
  self-identifying via the new `RunManifest.instrument` lineage field (C18) — *not*
  stamped on `FamilySelection` (there is no within-family winner to annotate). The
  inferential half is now structurally built; the per-candidate OOS bootstrap (#139,
  cycle 0075) is its adjacent significance read.
- **`aura-std` contents** — substantively populated (~30 node modules): SMA/EMA,
  arithmetic (`Add`/`Sub`/`Mul`/`Sqrt`/`LinComb`), logic (`And`/`Gt`/`Latch`/`EqConst`),
  the `Delay` z⁻¹ register, `Resample`, `RollingMin`/`RollingMax`, `Session`, the R chain
  (`Bias`/`FixedStop`/`Sizer`/`PositionManagement`), the legacy `SimBroker` pip yardstick,
  the cost-model graph (`CostNode`/`CostRunner`/`CostSum` + `ConstantCost`/`VolSlippageCost`/
  `CarryCost`), and the `Recorder`/`GatedRecorder`/`SeriesReducer` sinks. Further blocks
  land demand-driven as the walking-skeleton needs them.
- **`strategies/` split** — a later split, *inside a project*, of top-level
  strategies from reusable building blocks in `nodes/`; not a day-1 cut.
- **Sequencing** — the runnable single-harness *substrate* comes first (walking
  skeleton: a closed harness that runs deterministically and records via a sink);
  the World/meta layer (C21) and the playground trace-explorer (C22) are the
  differentiating layers that follow — you orchestrate and visualize a thing that
  must first run once.
