refactor: split the aura-std roster into C28 layer crates

Phase 4 of the Stratification milestone. aura-std held four C28 ladder
layers in one roster; this cuts them into layer-aligned, aura-core-only
node crates so the import direction is enforced by the crate graph:

- aura-std        — engine nodes only (arithmetic/logic/rolling + sinks)
- aura-market     — session, resample
- aura-strategy   — bias, stops, sizer, cost-model machinery
- aura-backtest   — sim_broker, position_management
- aura-vocabulary — the relocated closed std_vocabulary roster

Node modules move verbatim (byte-identical renames); consumers are
rewired by import path only. A new structural test
(aura-vocabulary/tests/c28_layering.rs) asserts each node crate's
[dependencies] stay within its C28-permitted inner set, catching the
acyclic-but-outward violation the compiler misses.

Behaviour byte-identical: full workspace suite green (1448 tests), no
golden edited, clippy -D warnings clean. C28 Status block updated.

closes #288

Cargo.lock

@@ -105,6 +105,13 @@ dependencies = [
  "serde_json",
 ]
 
+[[package]]
+name = "aura-backtest"
+version = "0.1.0"
+dependencies = [
+ "aura-core",
+]
+
 [[package]]
 name = "aura-bench"
 version = "0.1.0"
@@ -139,6 +146,7 @@ dependencies = [
 name = "aura-cli"
 version = "0.1.0"
 dependencies = [
+ "aura-backtest",
  "aura-campaign",
  "aura-composites",
  "aura-core",
@@ -147,6 +155,8 @@ dependencies = [
  "aura-registry",
  "aura-research",
  "aura-std",
+ "aura-strategy",
+ "aura-vocabulary",
  "clap",
  "data-server",
  "libc",
@@ -162,9 +172,11 @@ dependencies = [
 name = "aura-composites"
 version = "0.1.0"
 dependencies = [
+ "aura-backtest",
  "aura-core",
  "aura-engine",
  "aura-std",
+ "aura-strategy",
  "serde_json",
 ]
 
@@ -181,8 +193,12 @@ name = "aura-engine"
 version = "0.1.0"
 dependencies = [
  "aura-analysis",
+ "aura-backtest",
  "aura-core",
+ "aura-market",
  "aura-std",
+ "aura-strategy",
+ "aura-vocabulary",
  "chrono",
  "chrono-tz",
  "rayon",
@@ -194,15 +210,27 @@ dependencies = [
 name = "aura-ingest"
 version = "0.1.0"
 dependencies = [
+ "aura-backtest",
  "aura-core",
  "aura-engine",
+ "aura-market",
  "aura-std",
+ "aura-strategy",
  "chrono",
  "chrono-tz",
  "data-server",
  "zip",
 ]
 
+[[package]]
+name = "aura-market"
+version = "0.1.0"
+dependencies = [
+ "aura-core",
+ "chrono",
+ "chrono-tz",
+]
+
 [[package]]
 name = "aura-registry"
 version = "0.1.0"
@@ -211,6 +239,8 @@ dependencies = [
  "aura-engine",
  "aura-research",
  "aura-std",
+ "aura-strategy",
+ "aura-vocabulary",
  "serde",
  "serde_json",
 ]
@@ -229,11 +259,32 @@ dependencies = [
 name = "aura-std"
 version = "0.1.0"
 dependencies = [
+ "aura-backtest",
  "aura-core",
+ "aura-strategy",
  "chrono",
  "chrono-tz",
 ]
 
+[[package]]
+name = "aura-strategy"
+version = "0.1.0"
+dependencies = [
+ "aura-core",
+]
+
+[[package]]
+name = "aura-vocabulary"
+version = "0.1.0"
+dependencies = [
+ "aura-backtest",
+ "aura-core",
+ "aura-market",
+ "aura-std",
+ "aura-strategy",
+ "toml",
+]
+
 [[package]]
 name = "autocfg"
 version = "1.5.1"

Cargo.toml

@@ -11,6 +11,10 @@ resolver = "3"
 members = [
     "crates/aura-core",
     "crates/aura-std",
+    "crates/aura-vocabulary",
+    "crates/aura-market",
+    "crates/aura-strategy",
+    "crates/aura-backtest",
     "crates/aura-engine",
     "crates/aura-analysis",
     "crates/aura-composites",

crates/aura-backtest/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "aura-backtest"
+edition.workspace = true
+version.workspace = true
+license.workspace = true
+publish.workspace = true
+
+[dependencies]
+aura-core = { path = "../aura-core" }

crates/aura-backtest/src/lib.rs

@@ -0,0 +1,12 @@
+//! `aura-backtest` — the backtest-execution node layer (C28): simulated execution
+//! without money (the `SimBroker` pip yardstick, position management), measured in
+//! R. Depends only on `aura-core`.
+
+mod position_management;
+mod sim_broker;
+
+pub use position_management::{
+    ExitReason, FIELD_NAMES as PM_FIELD_NAMES, PositionManagement,
+    RECORD_KINDS as PM_RECORD_KINDS, WIDTH as PM_WIDTH,
+};
+pub use sim_broker::SimBroker;

crates/aura-cli/Cargo.toml

@@ -22,6 +22,9 @@ aura-research = { path = "../aura-research" }
 # and renders its outcome (#198).
 aura-campaign = { path = "../aura-campaign" }
 aura-std = { path = "../aura-std" }
+aura-strategy = { path = "../aura-strategy" }
+aura-backtest = { path = "../aura-backtest" }
+aura-vocabulary = { path = "../aura-vocabulary" }
 aura-ingest = { path = "../aura-ingest" }
 # data-server: the local M1 archive `aura run --real` streams from. Mirrors the
 # git line in crates/aura-ingest/Cargo.toml verbatim (same source of truth).

crates/aura-cli/src/campaign_run.rs

@@ -31,7 +31,7 @@ use aura_research::{
     campaign_to_json, content_id_of, parse_campaign, parse_process, validate_campaign,
     validate_process, CampaignDoc, CostSpec, DocRef,
 };
-use aura_std::{CarryCost, ConstantCost, VolSlippageCost};
+use aura_strategy::{CarryCost, ConstantCost, VolSlippageCost};
 
 use crate::project::Env;
 use crate::research_docs::{
@@ -1358,7 +1358,8 @@ mod tests {
     /// (bind_axes surfaces THAT case as its own named fault once the
     /// reopened space is built downstream).
     fn raw_bound_overrides_of_selects_axes_naming_a_bound_param() {
-        use aura_std::{Bias, Sma};
+        use aura_strategy::Bias;
+        use aura_std::Sma;
         let raw_signal = Composite::new(
             "fixture",
             vec![
@@ -1555,9 +1556,9 @@ mod tests {
     /// variant reconstruction with no compiler error; this pin makes it loud.
     fn every_cost_builder_declares_exactly_one_distinct_knob() {
         let knobs: Vec<String> = [
-            aura_std::ConstantCost::builder(),
-            aura_std::VolSlippageCost::builder(),
-            aura_std::CarryCost::builder(),
+            aura_strategy::ConstantCost::builder(),
+            aura_strategy::VolSlippageCost::builder(),
+            aura_strategy::CarryCost::builder(),
         ]
         .iter()
         .map(|b| {

crates/aura-cli/src/graph_construct.rs

@@ -2,7 +2,7 @@
 //! JSON op-list document deserializes into the `OpDoc` DTO (so the engine `Op`
 //! stays serde-free), which maps 1:1 into `aura_engine::Op`. The `aura graph
 //! build` / `aura graph introspect` subcommands here drive these ops through the
-//! injected `aura_std::std_vocabulary`.
+//! injected `aura_vocabulary::std_vocabulary`.
 
 use std::collections::BTreeMap;
 use std::path::Path;
@@ -16,7 +16,7 @@ use serde::Deserialize;
 // `std_vocabulary` is now only reached through `crate::project::Env::resolve` in
 // production code; tests still exercise it directly.
 #[cfg(test)]
-use aura_std::std_vocabulary;
+use aura_vocabulary::std_vocabulary;
 
 /// The wire DTO for one construction op — the document's by-identifier shape,
 /// internally tagged by `"op"`, mapped into the serde-free engine `Op`. Bind

crates/aura-cli/src/main.rs

@@ -30,16 +30,16 @@ use aura_registry::{
     FamilyMember, Generalization, NameKind, PlateauMode, Registry, RunTraces,
     DEFLATION_BLOCK_LEN, DEFLATION_N_RESAMPLES,
 };
+use aura_backtest::{SimBroker, PM_FIELD_NAMES, PM_RECORD_KINDS};
 use aura_std::{
-    cost_port, GatedRecorder, LinComb, Recorder, RollingMax, RollingMin,
-    SeriesReducer, SimBroker, Sub, GEOMETRY_WIDTH, PM_FIELD_NAMES,
-    PM_RECORD_KINDS,
+    GatedRecorder, LinComb, Recorder, RollingMax, RollingMin, SeriesReducer, Sub,
 };
+use aura_strategy::{cost_port, GEOMETRY_WIDTH};
 // `std_vocabulary` is now only reached through `project::Env::resolve` in production
 // code; the test module still builds reference blueprints against it directly, so
 // the import is test-only.
 #[cfg(test)]
-use aura_std::std_vocabulary;
+use aura_vocabulary::std_vocabulary;
 // `Delay` is now only used by the test-only `r_breakout_signal` carve (#159 cut 2's
 // fused-builder retirement dropped the production caller); the import is test-only.
 #[cfg(test)]
@@ -61,9 +61,11 @@ use aura_engine::ColumnarTrace;
 // `Bias`/`Ema`/`Sma` are only reached from the test module; the imports are
 // test-only, mirroring `Delay`/`Scale` above.
 #[cfg(test)]
-use aura_std::{Bias, Ema, Sma};
+use aura_strategy::Bias;
 #[cfg(test)]
-use aura_std::{ConstantCost, VolSlippageCost};
+use aura_std::{Ema, Sma};
+#[cfg(test)]
+use aura_strategy::{ConstantCost, VolSlippageCost};
 use std::sync::mpsc;
 use std::sync::LazyLock;
 use std::collections::{BTreeMap, BTreeSet, HashSet};

crates/aura-cli/src/project.rs

@@ -14,7 +14,7 @@ use aura_core::project::{
 };
 use aura_engine::ProjectProvenance;
 use aura_registry::{Registry, TraceStore};
-use aura_std::{std_vocabulary, std_vocabulary_types};
+use aura_vocabulary::{std_vocabulary, std_vocabulary_types};
 use sha2::{Digest, Sha256};
 use std::fmt;
 use std::path::{Path, PathBuf};

crates/aura-cli/tests/cli_run.rs

@@ -4336,7 +4336,7 @@ fn sweep_and_walkforward_refuse_trace_with_a_forward_pointer() {
 #[test]
 fn aura_sweep_persists_the_canonical_blueprint_keyed_by_topology_hash() {
     use aura_engine::{blueprint_from_json, blueprint_to_json};
-    use aura_std::std_vocabulary;
+    use aura_vocabulary::std_vocabulary;
     use sha2::{Digest, Sha256};
 
     let cwd = temp_cwd("blueprint-sweep-store");

crates/aura-composites/Cargo.toml

@@ -14,6 +14,8 @@ publish.workspace = true
 aura-core = { path = "../aura-core" }
 aura-engine = { path = "../aura-engine" }
 aura-std = { path = "../aura-std" }
+aura-strategy = { path = "../aura-strategy" }
+aura-backtest = { path = "../aura-backtest" }
 
 [dev-dependencies]
 # serde_json: the risk_executor fixture round-trips a folded RunMetrics through

crates/aura-composites/src/lib.rs

@@ -17,10 +17,11 @@
 //! what C19/C23 DCE deletes), so it appears nowhere here.
 use aura_core::{PrimitiveBuilder, Scalar};
 use aura_engine::{Composite, GraphBuilder, NodeHandle};
-use aura_std::{
-    cost_port, intern_port, CostSum, Delay, Ema, FixedStop, LinComb, Mul,
-    PositionManagement, Sizer, Sqrt, Sub, VolTfStop, COST_FIELD_NAMES, GEOMETRY_WIDTH,
-    PM_FIELD_NAMES,
+use aura_backtest::{PositionManagement, PM_FIELD_NAMES};
+use aura_std::{Delay, Ema, LinComb, Mul, Sqrt, Sub};
+use aura_strategy::{
+    cost_port, intern_port, CostSum, FixedStop, Sizer, VolTfStop, COST_FIELD_NAMES,
+    GEOMETRY_WIDTH,
 };
 
 /// The volatility stop as a composition of primitives:

crates/aura-composites/tests/cost_graph.rs

@@ -5,7 +5,7 @@
 
 use aura_composites::cost_graph;
 use aura_core::Scalar;
-use aura_std::{ConstantCost, VolSlippageCost};
+use aura_strategy::{ConstantCost, VolSlippageCost};
 
 /// Two heterogeneous cost nodes: ConstantCost (no extras, index 0) and
 /// VolSlippageCost (one extra `volatility`, index 1). The composite exposes the 4

crates/aura-composites/tests/risk_executor.rs

@@ -10,7 +10,8 @@ use aura_core::{
 };
 use aura_composites::{risk_executor, StopRule};
 use aura_engine::{summarize_r, GraphBuilder, RunMetrics, VecSource};
-use aura_std::{Recorder, PM_FIELD_NAMES, PM_RECORD_KINDS};
+use aura_backtest::{PM_FIELD_NAMES, PM_RECORD_KINDS};
+use aura_std::Recorder;
 use std::sync::mpsc::channel;
 
 // The dense-record columns this fixture reads, named in lockstep with the sibling

crates/aura-engine/Cargo.toml

@@ -36,6 +36,10 @@ rayon = "1"
 # positionally, by index), so aura-std stays out of [dependencies] and the engine is
 # `-> aura-core` only. The node-naming composite-builders live in `aura-composites`.
 aura-std = { path = "../aura-std" }
+aura-market = { path = "../aura-market" }
+aura-strategy = { path = "../aura-strategy" }
+aura-backtest = { path = "../aura-backtest" }
+aura-vocabulary = { path = "../aura-vocabulary" }
 # chrono / chrono-tz build the Berlin-local-wall-clock epoch-ns timestamps the
 # GER40 session-breakout E2E fixture (tests/ger40_breakout.rs) feeds the engine,
 # exactly as `Session`'s own unit test does. Pinned to aura-std's versions (the

crates/aura-engine/src/blueprint.rs

@@ -1384,7 +1384,9 @@ mod tests {
     use crate::test_fixtures::{composite_sma_cross_harness, synthetic_prices};
     use crate::{f64_field, summarize, ParamRange, RandomSpace, RunManifest, VecSource};
     use aura_core::{Cell, Ctx, FieldSpec, Firing, NodeSchema, Timestamp};
-    use aura_std::{Bias, Ema, LinComb, Recorder, SimBroker, Sma, Sub};
+    use aura_backtest::SimBroker;
+    use aura_std::{Ema, LinComb, Recorder, Sma, Sub};
+    use aura_strategy::Bias;
     use std::sync::mpsc;
 
     /// One knob fanning into two sibling open params passes the gate; the
@@ -3122,7 +3124,8 @@ mod tests {
 
     #[test]
     fn param_space_reflects_only_open_knobs() {
-        use aura_std::{Bias, Sma};
+        use aura_strategy::Bias;
+        use aura_std::Sma;
         // "sma2_entry": Sma "bias" with length bound to 2 (a structural constant)
         // plus Bias "exp" whose `scale` stays open. The bound knob must be
         // absent from param_space; only the open one remains.
@@ -3148,7 +3151,8 @@ mod tests {
     /// order — the bound value becomes a default an axis may override.
     #[test]
     fn reopen_returns_a_bound_knob_to_param_space() {
-        use aura_std::{Bias, Sma};
+        use aura_strategy::Bias;
+        use aura_std::Sma;
         let strat = Composite::new(
             "sma2_entry",
             vec![
@@ -3169,7 +3173,8 @@ mod tests {
     /// error, not a silent no-op — open axes pass through without reopen.
     #[test]
     fn reopen_unknown_or_open_path_errors() {
-        use aura_std::{Bias, Sma};
+        use aura_strategy::Bias;
+        use aura_std::Sma;
         let strat = Composite::new(
             "sma2_entry",
             vec![
@@ -3190,7 +3195,8 @@ mod tests {
     /// carries the bound value (the default the CLI renders in --list-axes).
     #[test]
     fn bound_param_space_is_path_qualified_with_values() {
-        use aura_std::{Bias, Sma};
+        use aura_strategy::Bias;
+        use aura_std::Sma;
         let strat = Composite::new(
             "sma2_entry",
             vec![

crates/aura-engine/src/blueprint_serde.rs

@@ -244,7 +244,7 @@ fn reconstruct(
 }
 
 /// Load a blueprint from canonical JSON, resolving each primitive's type identity
-/// through the injected `resolve` (e.g. `aura_std::std_vocabulary`). The version
+/// through the injected `resolve` (e.g. `aura_vocabulary::std_vocabulary`). The version
 /// envelope is checked before the payload is reconstructed.
 pub fn blueprint_from_json(
     data: &str,
@@ -267,7 +267,8 @@ mod tests {
     use crate::harness::{Edge, Target};
     use crate::VecSource; // crate-root re-export (blueprint.rs tests import it the same way, e.g. :923)
     use aura_core::{Scalar, ScalarKind, Timestamp};
-    use aura_std::{Bias, Recorder, Sma, Sub};
+    use aura_std::{Recorder, Sma, Sub};
+    use aura_strategy::Bias;
     use std::sync::mpsc;
 
     // Open param point for the sink-free signal (fast.length is bound): [slow.length, bias.scale].
@@ -303,7 +304,7 @@ mod tests {
     fn serialized_blueprint_runs_bit_identical_to_rust_built() {
         let rust_built = crate::test_fixtures::sink_free_sma_cross_signal();
         let json = blueprint_to_json(&rust_built).expect("serializes");
-        let loaded = blueprint_from_json(&json, &|t| aura_std::std_vocabulary(t)).expect("loads");
+        let loaded = blueprint_from_json(&json, &|t| aura_vocabulary::std_vocabulary(t)).expect("loads");
 
         let trace_rust = run_recording(rust_built);
         let trace_loaded = run_recording(loaded);
@@ -316,7 +317,7 @@ mod tests {
     fn serializer_and_loader_are_inverse() {
         let original = crate::test_fixtures::sink_free_sma_cross_signal();
         let json = blueprint_to_json(&original).expect("serializes");
-        let loaded = blueprint_from_json(&json, &|t| aura_std::std_vocabulary(t)).expect("loads");
+        let loaded = blueprint_from_json(&json, &|t| aura_vocabulary::std_vocabulary(t)).expect("loads");
         // serialize -> load -> serialize is byte-stable (canonical round-trip identity)
         assert_eq!(json, blueprint_to_json(&loaded).expect("re-serializes"));
     }
@@ -339,7 +340,7 @@ mod tests {
             vec![OutField { node: 0, field: 0, name: "bias".into() }],
         );
         let json = blueprint_to_json(&outer).expect("serializes");
-        let loaded = blueprint_from_json(&json, &|t| aura_std::std_vocabulary(t)).expect("loads");
+        let loaded = blueprint_from_json(&json, &|t| aura_vocabulary::std_vocabulary(t)).expect("loads");
         assert_eq!(json, blueprint_to_json(&loaded).expect("re-serializes"));
         // the nested composite survived as a composite, not flattened
         assert!(json.contains(r#"{"composite":{"name":"sma_cross""#), "nested composite preserved");
@@ -370,7 +371,7 @@ mod tests {
         assert_ne!(plain_json, doced_json, "the doc is canonical-byte-bearing");
         assert!(doced_json.contains("why this graph"), "doc serialized: {doced_json}");
         assert!(!plain_json.contains("\"doc\""), "absent doc emits no key: {plain_json}");
-        let loaded = blueprint_from_json(&doced_json, &|t| aura_std::std_vocabulary(t)).expect("loads");
+        let loaded = blueprint_from_json(&doced_json, &|t| aura_vocabulary::std_vocabulary(t)).expect("loads");
         assert_eq!(loaded.doc(), Some("why this graph: the spread detects trend turns"));
         assert_eq!(doced_json, blueprint_to_json(&loaded).expect("re-serializes"), "round-trip byte-stable");
         assert_eq!(
@@ -395,7 +396,7 @@ mod tests {
         let tapped_json = blueprint_to_json(&tapped).expect("serializes");
         assert_ne!(plain_json, tapped_json, "taps are canonical-byte-bearing");
         assert!(!plain_json.contains("\"taps\""), "absent taps emit no key: {plain_json}");
-        let loaded = blueprint_from_json(&tapped_json, &|t| aura_std::std_vocabulary(t)).expect("loads");
+        let loaded = blueprint_from_json(&tapped_json, &|t| aura_vocabulary::std_vocabulary(t)).expect("loads");
         assert_eq!(loaded.taps(), tapped.taps());
         assert_eq!(tapped_json, blueprint_to_json(&loaded).expect("re-serializes"), "round-trip byte-stable");
     }
@@ -431,14 +432,14 @@ mod tests {
         let json = r#"{"format_version":1,"blueprint":{"name":"x","nodes":[{"primitive":{"type":"NoSuchNode"}}]}}"#;
         // `.err().unwrap()` (not `.unwrap_err()`): the Ok type `Composite` holds a
         // build closure and is not `Debug`, which `unwrap_err`'s bound would require.
-        let err = blueprint_from_json(json, &|t| aura_std::std_vocabulary(t)).err().unwrap();
+        let err = blueprint_from_json(json, &|t| aura_vocabulary::std_vocabulary(t)).err().unwrap();
         assert!(matches!(err, LoadError::UnknownNodeType(t) if t == "NoSuchNode"));
     }
 
     #[test]
     fn unsupported_version_fails_named() {
         let json = r#"{"format_version":2,"blueprint":{"name":"x","nodes":[]}}"#;
-        let err = blueprint_from_json(json, &|t| aura_std::std_vocabulary(t)).err().unwrap();
+        let err = blueprint_from_json(json, &|t| aura_vocabulary::std_vocabulary(t)).err().unwrap();
         assert!(matches!(err, LoadError::UnsupportedVersion { found: 2, supported: 1 }));
     }
 
@@ -466,7 +467,7 @@ mod tests {
         assert_ne!(with_unknown, canonical, "probe must actually inject unknown keys");
 
         // tolerated, not refused
-        let loaded = blueprint_from_json(&with_unknown, &|t| aura_std::std_vocabulary(t))
+        let loaded = blueprint_from_json(&with_unknown, &|t| aura_vocabulary::std_vocabulary(t))
             .expect("an unknown optional field is tolerated, not refused");
 
         // the unknown keys did not leak into the graph: re-serialization equals the
@@ -474,7 +475,7 @@ mod tests {
         assert_eq!(blueprint_to_json(&loaded).expect("re-serializes"), canonical);
 
         // and the loaded graph runs bit-identically to the plain canonical one (C1).
-        let plain = blueprint_from_json(&canonical, &|t| aura_std::std_vocabulary(t)).expect("loads");
+        let plain = blueprint_from_json(&canonical, &|t| aura_vocabulary::std_vocabulary(t)).expect("loads");
         assert_eq!(
             run_recording(loaded),
             run_recording(plain),
@@ -655,9 +656,9 @@ mod tests {
     }
 
     // The resolver used by the gang-serde tests below (mirrors the inline
-    // `&|t| aura_std::std_vocabulary(t)` closure the rest of this module uses).
+    // `&|t| aura_vocabulary::std_vocabulary(t)` closure the rest of this module uses).
     fn fixture_resolver() -> impl Fn(&str) -> Option<PrimitiveBuilder> {
-        |t: &str| aura_std::std_vocabulary(t)
+        |t: &str| aura_vocabulary::std_vocabulary(t)
     }
 
     // Shared topology: two open SMAs feeding a `Sub`. `ganged_fixture_named`

crates/aura-engine/src/builder.rs

@@ -344,7 +344,9 @@ mod tests {
     use crate::test_fixtures::sma_cross as hand_sma_cross;
     use crate::{Composite, OutField, Role, Target};
     use aura_core::{Firing, ScalarKind};
-    use aura_std::{Bias, Recorder, SimBroker, Sma, Sub};
+    use aura_backtest::SimBroker;
+    use aura_std::{Recorder, Sma, Sub};
+    use aura_strategy::Bias;
     use std::sync::mpsc;
 
     /// The `sma_cross` sub-composite authored through the builder.

crates/aura-engine/src/construction.rs

@@ -472,7 +472,7 @@ pub fn replay(
 mod tests {
     use super::{GraphSession, Op, OpError};
     use aura_core::{BindOpError, Scalar, ScalarKind};
-    use aura_std::std_vocabulary;
+    use aura_vocabulary::std_vocabulary;
 
     fn session(name: &str) -> GraphSession<'static> {
         GraphSession::new(name, &std_vocabulary)
@@ -736,7 +736,7 @@ mod tests {
             Op::Tap { from: "fast.value".into(), as_name: "fast_ma".into() },
             Op::Expose { from: "sub.value".into(), as_name: "bias".into() },
         ];
-        let flat = super::replay("g", ops, &aura_std::std_vocabulary)
+        let flat = super::replay("g", ops, &aura_vocabulary::std_vocabulary)
             .expect("replays")
             .compile_with_params(&[Scalar::i64(2), Scalar::i64(4)])
             .expect("compiles");
@@ -949,7 +949,7 @@ mod tests {
         let finalize = ops.len();
         // `.err()` not `.unwrap_err()`: the Ok arm `Composite` holds build closures
         // and is not `Debug`.
-        let (idx, _err) = super::replay("g", ops, &aura_std::std_vocabulary)
+        let (idx, _err) = super::replay("g", ops, &aura_vocabulary::std_vocabulary)
             .err()
             .expect("a cyclic op-list must be rejected (DAG invariant 5 / C9)");
         // An eager realisation attributes the fault to the closing connect op; a
@@ -976,7 +976,7 @@ mod tests {
             Op::Expose { from: "s.value".into(), as_name: "out".into() },
         ];
         assert!(
-            super::replay("g", ops, &aura_std::std_vocabulary).is_err(),
+            super::replay("g", ops, &aura_vocabulary::std_vocabulary).is_err(),
             "a self-loop op-list must be rejected (DAG invariant 5 / C9)"
         );
     }
@@ -990,7 +990,7 @@ mod tests {
         ];
         // `.err().unwrap()` rather than `.unwrap_err()`: the Ok arm `Composite` is
         // not `Debug` (it holds build closures), which `unwrap_err` would require.
-        let err = super::replay("g", ops, &aura_std::std_vocabulary).err().unwrap();
+        let err = super::replay("g", ops, &aura_vocabulary::std_vocabulary).err().unwrap();
         assert_eq!(err, (1, OpError::UnknownNodeType("Nope".into())));
     }
 
@@ -1004,7 +1004,8 @@ mod tests {
     fn replay_built_signal_compiles_identically_to_graphbuilder() {
         use crate::GraphBuilder;
         use aura_core::Scalar;
-        use aura_std::{Bias, Sma, Sub};
+        use aura_std::{Sma, Sub};
+        use aura_strategy::Bias;
 
         // param space of the flat root: fast.length(i64), slow.length(i64),
         // bias.scale(f64) — same vector applied to both sides, so it cancels.
@@ -1023,7 +1024,7 @@ mod tests {
             Op::Connect { from: "sub.value".into(), to: "bias.signal".into() },
             Op::Expose { from: "bias.bias".into(), as_name: "bias".into() },
         ];
-        let replay_flat = super::replay("root", ops, &aura_std::std_vocabulary)
+        let replay_flat = super::replay("root", ops, &aura_vocabulary::std_vocabulary)
             .expect("replay resolves")
             .compile_with_params(&params)
             .expect("replay compiles");

crates/aura-engine/src/graph_model.rs

@@ -321,7 +321,8 @@ mod tests {
     use aura_core::{
         Cell, FieldSpec, Node, NodeSchema, PortSpec, PrimitiveBuilder, Scalar,
     };
-    use aura_std::{Bias, Recorder, Sma, Sub};
+    use aura_std::{Recorder, Sma, Sub};
+    use aura_strategy::Bias;
     use std::sync::mpsc;
 
     /// A bare node whose only purpose is to back a `PrimitiveBuilder` in a test.

crates/aura-engine/src/harness.rs

@@ -676,7 +676,9 @@ mod tests {
     // PortSpec / NodeSchema name the fixtures' declared signatures, brought in here
     // (production code reads them via the carried signatures, never naming the types).
     use aura_core::{FieldSpec, NodeSchema, PortSpec};
-    use aura_std::{Bias, Recorder, Sma, SimBroker, Sub, When};
+    use aura_backtest::SimBroker;
+    use aura_std::{Recorder, Sma, Sub, When};
+    use aura_strategy::Bias;
     use std::sync::mpsc;
 
     /// Build an f64 source stream from (timestamp, value) points.

crates/aura-engine/src/report.rs

@@ -312,7 +312,9 @@ mod tests {
     use super::*;
     use crate::{Edge, FlatGraph, Harness, SourceSpec, Target, VecSource};
     use aura_core::{Firing, NodeSchema, PortSpec, ScalarKind};
-    use aura_std::{Bias, Recorder, SimBroker, Sma, Sub};
+    use aura_backtest::SimBroker;
+    use aura_std::{Recorder, Sma, Sub};
+    use aura_strategy::Bias;
     use std::sync::mpsc;
 
     #[test]

crates/aura-engine/src/test_fixtures.rs

@@ -6,7 +6,9 @@
 
 use crate::{BlueprintNode, Composite, Edge, OutField, Role, Target};
 use aura_core::{Firing, Scalar, ScalarKind, Timestamp};
-use aura_std::{Bias, Recorder, SimBroker, Sma, Sub};
+use aura_backtest::SimBroker;
+use aura_std::{Recorder, Sma, Sub};
+use aura_strategy::Bias;
 use std::sync::mpsc;
 
 /// Seven synthetic F64 ticks driving the harness; deterministic input fixture.

crates/aura-engine/tests/blueprint_serde_e2e.rs

@@ -1,7 +1,7 @@
 //! End-to-end coverage for blueprint serialization (C24, cycle 0087): a
 //! param-generic `Composite` is projected to canonical, versioned JSON
 //! (`blueprint_to_json`) and reconstructed from it (`blueprint_from_json`) through
-//! an **injected** node-vocabulary resolver (`aura_std::std_vocabulary`).
+//! an **injected** node-vocabulary resolver (`aura_vocabulary::std_vocabulary`).
 //!
 //! The in-module tests in `blueprint_serde.rs` reach into crate internals
 //! (`crate::test_fixtures::sink_free_sma_cross_signal`, the crate-private
@@ -19,7 +19,9 @@ use aura_engine::{
     blueprint_from_json, blueprint_identity_json, blueprint_to_json, BlueprintNode, Composite,
     Edge, LoadError, OutField, Role, Target, VecSource, BLUEPRINT_FORMAT_VERSION,
 };
-use aura_std::{std_vocabulary, Bias, Recorder, Sma, Sub};
+use aura_std::{Recorder, Sma, Sub};
+use aura_strategy::Bias;
+use aura_vocabulary::std_vocabulary;
 
 /// Seven synthetic F64 ticks (mirrors the crate-private `synthetic_prices`):
 /// short enough that the fast (2) and slow (4) SMA windows warm up within the
@@ -102,7 +104,7 @@ fn run_recording(signal: Composite) -> Vec<(Timestamp, Vec<Scalar>)> {
 
 /// Property (C24 acceptance, through the public seam): a blueprint authored via the
 /// exported `Composite` builder, serialized to JSON, then loaded back through
-/// `blueprint_from_json` + the injected `aura_std::std_vocabulary` and run, records
+/// `blueprint_from_json` + the injected `aura_vocabulary::std_vocabulary` and run, records
 /// a `bias` trace **byte-identical** to the Rust-built twin's run — proven entirely
 /// through `aura_engine`/`aura_std` public exports (the World/cdylib seam C24
 /// serves). The serialization round-trip is behaviour-preserving (C1): same input,

crates/aura-engine/tests/construction_e2e.rs

@@ -7,7 +7,7 @@
 //! (`crate::GraphBuilder`, `crate::CompileError`, `super::replay`). These tests
 //! use only the **exported** surface — `aura_engine::{replay, Op, OpError,
 //! GraphBuilder, Composite, FlatGraph, Scalar, ScalarKind}` plus the injected
-//! `aura_std::std_vocabulary` — the exact seam the iteration-2 CLI (`aura graph
+//! `aura_vocabulary::std_vocabulary` — the exact seam the iteration-2 CLI (`aura graph
 //! build`/`introspect`) and the World consume. A refactor that made `Op`,
 //! `OpError`, `replay`, or a needed re-export (`ScalarKind`, `Scalar`)
 //! unreachable across the crate boundary would break that consumer while leaving
@@ -15,7 +15,9 @@
 //! addition to the per-property invariants below.
 
 use aura_engine::{replay, GraphBuilder, Op, OpError, Scalar, ScalarKind};
-use aura_std::{std_vocabulary, Bias, Sma, Sub};
+use aura_std::{Sma, Sub};
+use aura_strategy::Bias;
+use aura_vocabulary::std_vocabulary;
 
 /// The flat root's open param point: fast.length(i64), slow.length(i64),
 /// bias.scale(f64), in param-space traversal order. The same vector is applied to
@@ -45,7 +47,7 @@ fn signal_ops() -> Vec<Op> {
 }
 
 /// Property (C24 acceptance-1, through the public seam): an op-script replayed via
-/// the exported `replay` + the injected `aura_std::std_vocabulary` compiles to a
+/// the exported `replay` + the injected `aura_vocabulary::std_vocabulary` compiles to a
 /// `FlatGraph` whose index-wired topology (`edges`) and lowered bound sources
 /// (`sources`) are **identical** to the same signal hand-wired on the exported
 /// `GraphBuilder` surface and compiled with the same param point. The two

crates/aura-engine/tests/ger40_breakout.rs

@@ -32,7 +32,9 @@ use std::sync::mpsc;
 
 use aura_core::{NodeSchema, Scalar, ScalarKind, Timestamp};
 use aura_engine::{Edge, FlatGraph, Harness, Source, SourceSpec, Target, VecSource};
-use aura_std::{And, Delay, EqConst, Gt, Latch, Recorder, Resample, Session, SimBroker};
+use aura_backtest::SimBroker;
+use aura_market::{Resample, Session};
+use aura_std::{And, Delay, EqConst, Gt, Latch, Recorder};
 use chrono::TimeZone;
 use chrono_tz::Europe::Berlin;
 

crates/aura-engine/tests/list_sweep_e2e.rs

@@ -14,7 +14,9 @@ use aura_engine::{
     f64_field, summarize, sweep, BlueprintNode, Composite, Edge, ListSpace, OutField, ParamSpec,
     Role, RunManifest, RunReport, Scalar, SweepError, Target, VecSource,
 };
-use aura_std::{Bias, Recorder, SimBroker, Sma, Sub};
+use aura_backtest::SimBroker;
+use aura_std::{Recorder, Sma, Sub};
+use aura_strategy::Bias;
 
 /// Seven synthetic F64 ticks — the same fixture shape as `random_sweep_e2e.rs`,
 /// short enough that small SMA windows warm up deterministically.

crates/aura-engine/tests/ohlc_from_blueprint_data.rs

@@ -11,7 +11,8 @@ use std::sync::mpsc;
 
 use aura_core::{Firing, Scalar, ScalarKind, Timestamp};
 use aura_engine::{blueprint_from_json, BlueprintNode, Composite, Edge, Role, Target, VecSource};
-use aura_std::{std_vocabulary, Recorder};
+use aura_std::Recorder;
+use aura_vocabulary::std_vocabulary;
 
 // value = (high - low) + (close - open): every column is load-bearing, so any
 // mis-pairing of roles to sources (or a wrong merge tie-break) changes the

crates/aura-engine/tests/r_sma_e2e.rs

@@ -27,10 +27,8 @@
 
 use aura_core::{AnyColumn, Ctx, Node, Scalar, ScalarKind, Timestamp};
 use aura_engine::{PositionAction, RMetrics, derive_position_events, summarize_r};
-use aura_std::{
-    ConstantCost, CostSum, FixedStop, PM_FIELD_NAMES, PM_RECORD_KINDS, PM_WIDTH,
-    PositionManagement, VolSlippageCost,
-};
+use aura_backtest::{PM_FIELD_NAMES, PM_RECORD_KINDS, PM_WIDTH, PositionManagement};
+use aura_strategy::{ConstantCost, CostSum, FixedStop, VolSlippageCost};
 
 // The indices `report.rs::summarize_r` reads the dense record by. Re-declared here
 // (the consumer's `r_col` module is private to `aura-engine`) so the guard test can
@@ -267,7 +265,7 @@ fn net_of_cost_is_charged_per_r_so_a_wider_stop_dilutes_it() {
     assert!(tight_cost > wide_cost, "a tighter stop must pay more R per fixed price-unit cost");
 }
 
-/// Drive the REAL `aura_std::ConstantCost(c)` node over a recorded PM `ledger`,
+/// Drive the REAL `aura_strategy::ConstantCost(c)` node over a recorded PM `ledger`,
 /// node-by-node off the producer's own `closed`/`open`/`entry_price`/`stop_price`
 /// columns — the actual cost producer the run-path graph taps (not an algebraic stand-in
 /// like `const_cost_stream`). Returns the node's 3-wide `[cost_in_r, cum_cost_in_r,
@@ -336,7 +334,7 @@ fn net_r_equity_final_sample_agrees_with_summarize_r_net_total() {
     );
 }
 
-/// Drive the REAL `aura_std::VolSlippageCost(k)` node over a recorded PM `ledger`
+/// Drive the REAL `aura_strategy::VolSlippageCost(k)` node over a recorded PM `ledger`
 /// with a constant `vol` per cycle — the run-path's vol-slippage producer. Returns
 /// the node's 3-wide `[cost_in_r, cum_cost_in_r, open_cost_in_r]` rows, co-temporal
 /// 1:1 with `ledger`.
@@ -367,7 +365,7 @@ fn vol_slippage_node_stream(
         .collect()
 }
 
-/// Drive the REAL `aura_std::CostSum(n)` aggregator over `n` co-temporal cost
+/// Drive the REAL `aura_strategy::CostSum(n)` aggregator over `n` co-temporal cost
 /// streams, summing them per-field — the run-path's cost-graph output node.
 fn cost_sum_node_stream(streams: &[&[(Timestamp, Vec<Scalar>)]]) -> Vec<(Timestamp, Vec<Scalar>)> {
     let n = streams.len();

crates/aura-engine/tests/random_sweep_e2e.rs

@@ -18,7 +18,9 @@ use aura_engine::{
     f64_field, summarize, sweep, BlueprintNode, Composite, Edge, OutField, ParamRange, ParamSpec,
     RandomSpace, Role, RunManifest, RunReport, Scalar, Space, SweepError, Target, VecSource,
 };
-use aura_std::{Bias, Recorder, SimBroker, Sma, Sub};
+use aura_backtest::SimBroker;
+use aura_std::{Recorder, Sma, Sub};
+use aura_strategy::Bias;
 
 /// Seven synthetic F64 ticks (mirrors the crate-private `synthetic_prices`):
 /// short enough that small SMA windows warm up, so every run yields finite,

crates/aura-engine/tests/reopen_rebuild_e2e.rs

@@ -13,7 +13,8 @@
 
 use aura_core::{Scalar, ScalarKind};
 use aura_engine::{Composite, Role, Target};
-use aura_std::{Bias, Sma};
+use aura_std::Sma;
+use aura_strategy::Bias;
 
 /// A single bound `Sma`, wired from a root role so it compiles standalone.
 fn one_bound_sma() -> Composite {

crates/aura-engine/tests/rsi_from_blueprint_data.rs

@@ -1,7 +1,7 @@
 //! Acceptance proof for issue #236: an **RSI-class** signal — the classic
 //! gain/loss split of the price change and the smoothed **ratio** of average gain
 //! to average loss — composes *purely from blueprint data* through the injected
-//! `aura_std::std_vocabulary` and runs to hand-computable RS values. This is the
+//! `aura_vocabulary::std_vocabulary` and runs to hand-computable RS values. This is the
 //! property that pins the four std-vocabulary gaps the issue names as a single
 //! honest behaviour: `Div`, a `Const` source, `Abs`, and pairwise `Max`/`Min`.
 //!
@@ -24,7 +24,8 @@ use std::sync::mpsc;
 
 use aura_core::{Firing, Scalar, ScalarKind, Timestamp};
 use aura_engine::{blueprint_from_json, BlueprintNode, Composite, Edge, Role, Target, VecSource};
-use aura_std::{std_vocabulary, Recorder};
+use aura_std::Recorder;
+use aura_vocabulary::std_vocabulary;
 
 // The RSI-class signal as blueprint data. Raw price fans out to a zero `Const`
 // (its clock is the price role), a `Delay[1]`, and a `Sub`; `delta = price - prev`

crates/aura-engine/tests/streaming_reduction_equivalence.rs

@@ -6,7 +6,8 @@
 
 use aura_core::{AnyColumn, Ctx, Node, Scalar, ScalarKind, Timestamp};
 use aura_engine::{summarize, summarize_r};
-use aura_std::{GatedRecorder, SeriesReducer, PM_RECORD_KINDS, PM_WIDTH};
+use aura_backtest::{PM_RECORD_KINDS, PM_WIDTH};
+use aura_std::{GatedRecorder, SeriesReducer};
 use std::sync::mpsc;
 
 const CLOSED: usize = 0;

crates/aura-engine/tests/streaming_reduction_memory.rs

@@ -12,7 +12,8 @@ use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::mpsc;
 
 use aura_core::{AnyColumn, Ctx, Node, Scalar, ScalarKind, Timestamp};
-use aura_std::{GatedRecorder, PM_RECORD_KINDS, PM_WIDTH};
+use aura_backtest::{PM_RECORD_KINDS, PM_WIDTH};
+use aura_std::GatedRecorder;
 
 struct CountingAlloc;
 static LIVE: AtomicUsize = AtomicUsize::new(0);

crates/aura-engine/tests/when_e2e.rs

@@ -21,7 +21,8 @@ use std::sync::mpsc;
 
 use aura_core::{Firing, Scalar, ScalarKind, Timestamp};
 use aura_engine::{GraphBuilder, VecSource};
-use aura_std::{Abs, Gt, Recorder, Resample, When};
+use aura_market::Resample;
+use aura_std::{Abs, Gt, Recorder, When};
 
 /// A deterministic `f64` tick stream, no timestamps/randomness beyond a fixed
 /// literal sequence.

crates/aura-ingest/Cargo.toml

@@ -25,6 +25,9 @@ aura-engine = { path = "../aura-engine" }
 zip = "2"
 # the integration tests bootstrap a sample harness + fold a RunReport
 aura-std = { path = "../aura-std" }
+aura-market = { path = "../aura-market" }
+aura-strategy = { path = "../aura-strategy" }
+aura-backtest = { path = "../aura-backtest" }
 # chrono / chrono-tz build the Berlin-local-wall-clock window bounds + the
 # Session node's timezone for the real GER40 session-breakout example/test
 # (examples/ger40_breakout_real.rs, tests/ger40_breakout_real.rs). Pinned to

crates/aura-ingest/examples/shared/breakout_real.rs

@@ -43,7 +43,9 @@ use aura_engine::{
     join_on_ts, summarize, Composite, Edge, FlatGraph, GraphBuilder, Harness, RunManifest,
     RunReport, SourceSpec, Target,
 };
-use aura_std::{And, Delay, EqConst, Gt, Latch, Recorder, Resample, Session, SimBroker};
+use aura_backtest::SimBroker;
+use aura_market::{Resample, Session};
+use aura_std::{And, Delay, EqConst, Gt, Latch, Recorder};
 use chrono::TimeZone;
 use chrono_tz::Europe::Berlin;
 

crates/aura-ingest/tests/real_bars.rs

@@ -13,7 +13,9 @@ use aura_engine::{
     VecSource,
 };
 use aura_ingest::load_m1_window;
-use aura_std::{Bias, Recorder, SimBroker, Sma, Sub};
+use aura_backtest::SimBroker;
+use aura_std::{Recorder, Sma, Sub};
+use aura_strategy::Bias;
 use data_server::{DataServer, DEFAULT_DATA_PATH};
 
 /// Bootstrap the cycle-0007 two-sink signal-quality harness (mirrors

crates/aura-ingest/tests/streaming_seam.rs

@@ -13,7 +13,9 @@ use aura_engine::{
     Target,
 };
 use aura_ingest::{M1Field, M1FieldSource};
-use aura_std::{Bias, Recorder, SimBroker, Sma, Sub};
+use aura_backtest::SimBroker;
+use aura_std::{Recorder, Sma, Sub};
+use aura_strategy::Bias;
 use data_server::loader::CHUNK_SIZE;
 use data_server::{DataServer, DEFAULT_DATA_PATH};
 

crates/aura-market/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "aura-market"
+edition.workspace = true
+version.workspace = true
+license.workspace = true
+publish.workspace = true
+
+[dependencies]
+aura-core = { path = "../aura-core" }
+chrono = { version = "0.4", default-features = false, features = ["clock"] }
+chrono-tz = { version = "0.10", default-features = false }

crates/aura-market/src/lib.rs

@@ -0,0 +1,8 @@
+//! `aura-market` — the market-vocabulary node layer (C28): session anchoring and
+//! bar resampling over market data streams. Depends only on `aura-core`.
+
+mod resample;
+mod session;
+
+pub use resample::Resample;
+pub use session::{Session, SessionFrankfurt};

crates/aura-registry/Cargo.toml

@@ -24,3 +24,5 @@ serde_json = { workspace = true }
 # the referential-tier test's generic param-space fixture (a real vocabulary
 # resolver + a zero-arg node, not hand-rolled).
 aura-std = { path = "../aura-std" }
+aura-strategy = { path = "../aura-strategy" }
+aura-vocabulary = { path = "../aura-vocabulary" }

crates/aura-registry/src/lib.rs

@@ -1799,7 +1799,7 @@ mod tests {
         use aura_research::{Axis, DocRef};
 
         let reg = Registry::open(temp_family_dir("referential_tier"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
 
         // A minimal fixture composite with one OPEN param, built from a
         // zero-arg `aura-std` node (`Bias`) so `std_vocabulary` can actually
@@ -1812,7 +1812,7 @@ mod tests {
         // vocabulary-loadable composite" the test needs.
         let composite = Composite::new(
             "fixture",
-            vec![aura_std::Bias::builder().named("b").into()],
+            vec![aura_strategy::Bias::builder().named("b").into()],
             vec![],
             vec![],
             vec![],
@@ -1942,7 +1942,7 @@ mod tests {
     fn bias_fixture() -> aura_engine::Composite {
         aura_engine::Composite::new(
             "fixture",
-            vec![aura_std::Bias::builder().named("b").into()],
+            vec![aura_strategy::Bias::builder().named("b").into()],
             vec![],
             vec![],
             vec![],
@@ -1966,7 +1966,7 @@ mod tests {
     #[test]
     fn identity_index_lookup_backfills_and_resolves() {
         let reg = Registry::open(temp_family_dir("identity_backfill"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
         let (blueprint_json, content_id, identity_id) = seed_blueprint(&reg, &bias_fixture());
 
         // no index yet: the lookup answers via the scan fallback...
@@ -1983,7 +1983,7 @@ mod tests {
     #[test]
     fn identity_index_verified_hit_answers_without_a_store_walk() {
         let reg = Registry::open(temp_family_dir("identity_hit_no_walk"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
         let (blueprint_json, _content_id, identity_id) = seed_blueprint(&reg, &bias_fixture());
 
         // backfill the index, then poison the store: a DIRECTORY named like
@@ -2003,7 +2003,7 @@ mod tests {
     #[test]
     fn identity_index_legacy_store_backfills_in_one_pass() {
         let reg = Registry::open(temp_family_dir("identity_legacy_backfill"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
         let (_json_a, content_a, identity_a) = seed_blueprint(&reg, &bias_fixture());
         let (_json_b, content_b, identity_b) = seed_blueprint(&reg, &delay_fixture());
         assert_ne!(identity_a, identity_b, "fixtures must be identity-distinct");
@@ -2023,7 +2023,7 @@ mod tests {
     #[test]
     fn identity_index_stale_lines_degrade_to_scan_and_heal() {
         let reg = Registry::open(temp_family_dir("identity_stale_heals"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
         let (json_a, content_a, identity_a) = seed_blueprint(&reg, &bias_fixture());
         let (_json_b, content_b, _identity_b) = seed_blueprint(&reg, &delay_fixture());
 
@@ -2052,7 +2052,7 @@ mod tests {
     #[test]
     fn identity_index_unloadable_under_roster_stays_unmatched() {
         let reg = Registry::open(temp_family_dir("identity_unloadable"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
         let (_json, _content_id, identity_id) = seed_blueprint(&reg, &bias_fixture());
         reg.find_blueprint_by_identity(&identity_id, &resolve).expect("backfill");
 
@@ -2067,7 +2067,7 @@ mod tests {
     #[test]
     fn identity_index_garbage_line_does_not_break_resolution() {
         let reg = Registry::open(temp_family_dir("identity_garbage_line"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
         let (blueprint_json, _content_id, identity_id) = seed_blueprint(&reg, &bias_fixture());
 
         // a wholly-garbage index file must not break resolution (a
@@ -2089,7 +2089,7 @@ mod tests {
     #[test]
     fn identity_index_twin_store_converges_and_stops_growing() {
         let reg = Registry::open(temp_family_dir("identity_twin_converges"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
 
         // Two same-identity twins: the one-node Bias composite, built with
         // different debug names. Debug symbols are identity-blind, so the two
@@ -2097,7 +2097,7 @@ mod tests {
         let (_json_a, content_a, identity) = seed_blueprint(&reg, &bias_fixture());
         let twin = aura_engine::Composite::new(
             "fixture_twin",
-            vec![aura_std::Bias::builder().named("b_twin").into()],
+            vec![aura_strategy::Bias::builder().named("b_twin").into()],
             vec![],
             vec![],
             vec![],
@@ -2145,7 +2145,7 @@ mod tests {
         use aura_std::Sma;
 
         let reg = Registry::open(temp_family_dir("bound_axis_tier"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
 
         // A fixture composite with ONE bound param and NO open param, so the
         // reverse full-coverage check (every OPEN param must be bound by an
@@ -2234,7 +2234,7 @@ mod tests {
         use aura_engine::{blueprint_to_json, Composite};
 
         let reg = Registry::open(temp_family_dir("coverage_tier"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
 
         // A fixture composite with TWO open params, from two zero-arg `Bias`
         // nodes so `std_vocabulary` can load it on round-trip (the sibling test
@@ -2243,8 +2243,8 @@ mod tests {
         let composite = Composite::new(
             "fixture",
             vec![
-                aura_std::Bias::builder().named("b1").into(),
-                aura_std::Bias::builder().named("b2").into(),
+                aura_strategy::Bias::builder().named("b1").into(),
+                aura_strategy::Bias::builder().named("b2").into(),
             ],
             vec![],
             vec![],
@@ -2307,14 +2307,14 @@ mod tests {
         use aura_engine::{blueprint_to_json, Composite, Role, Target};
 
         let reg = Registry::open(temp_family_dir("binding_keys"));
-        let resolve = |t: &str| aura_std::std_vocabulary(t);
+        let resolve = |t: &str| aura_vocabulary::std_vocabulary(t);
 
         // The referential fixture composite (see
         // referential_tier_resolves_refs_and_checks_axes), plus ONE input
         // role so a binding key has something to name.
         let composite = Composite::new(
             "fixture",
-            vec![aura_std::Bias::builder().named("b").into()],
+            vec![aura_strategy::Bias::builder().named("b").into()],
             vec![],
             vec![Role {
                 name: "price".to_string(),

crates/aura-std/Cargo.toml

@@ -14,3 +14,7 @@ aura-core = { path = "../aura-core" }
 # zone + DST transitions.
 chrono = { version = "0.4", default-features = false, features = ["clock"] }
 chrono-tz = { version = "0.10", default-features = false }
+
+[dev-dependencies]
+aura-strategy = { path = "../aura-strategy" }
+aura-backtest = { path = "../aura-backtest" }

crates/aura-std/src/lib.rs

@@ -20,12 +20,7 @@
 mod abs;
 mod add;
 mod and;
-mod bias;
-mod carry_cost;
 mod const_node;
-mod constant_cost;
-mod cost;
-mod cost_sum;
 mod cumsum;
 mod delay;
 mod div;
@@ -35,42 +30,24 @@ mod gated_recorder;
 mod gt;
 mod latch;
 mod lincomb;
-mod longonly;
 mod max;
 mod min;
 mod mul;
-mod position_management;
 mod recorder;
-mod resample;
 mod rolling_max;
 mod rolling_min;
 mod scale;
 mod select;
 mod series_reducer;
-mod session;
 mod sign;
-mod sim_broker;
-mod sizer;
 mod sma;
 mod sqrt;
-mod stop_rule;
 mod sub;
-mod vocabulary;
-mod vol_slippage_cost;
-mod vol_tf_stop;
 mod when;
 pub use abs::Abs;
 pub use add::Add;
 pub use and::And;
-pub use bias::Bias;
-pub use carry_cost::CarryCost;
 pub use const_node::Const;
-pub use constant_cost::ConstantCost;
-pub use cost::{
-    cost_node_builder, cost_port, intern_port, ChargeMode, CostNode, CostRunner,
-    COST_FIELD_NAMES, COST_WIDTH, GEOMETRY_WIDTH,
-};
-pub use cost_sum::CostSum;
 pub use cumsum::CumSum;
 pub use delay::Delay;
 pub use div::Div;
@@ -80,30 +57,17 @@ pub use gated_recorder::GatedRecorder;
 pub use gt::Gt;
 pub use latch::Latch;
 pub use lincomb::LinComb;
-pub use longonly::LongOnly;
 pub use max::Max;
 pub use min::Min;
 pub use mul::Mul;
-pub use position_management::{
-    ExitReason, FIELD_NAMES as PM_FIELD_NAMES, PositionManagement, RECORD_KINDS as PM_RECORD_KINDS,
-    WIDTH as PM_WIDTH,
-};
 pub use recorder::Recorder;
-pub use resample::Resample;
 pub use rolling_max::RollingMax;
 pub use rolling_min::RollingMin;
 pub use scale::Scale;
 pub use select::Select;
 pub use series_reducer::SeriesReducer;
-pub use session::{Session, SessionFrankfurt};
 pub use sign::Sign;
-pub use sim_broker::SimBroker;
-pub use sizer::Sizer;
 pub use sma::Sma;
 pub use sqrt::Sqrt;
-pub use stop_rule::FixedStop;
 pub use sub::Sub;
-pub use vocabulary::{std_vocabulary, std_vocabulary_types};
-pub use vol_slippage_cost::VolSlippageCost;
-pub use vol_tf_stop::VolTfStop;
 pub use when::When;

crates/aura-std/src/sma.rs

@@ -202,7 +202,9 @@ mod tests {
 
     #[test]
     fn labels_carry_identifying_params() {
-        use crate::{Add, Bias, LinComb, Recorder, SimBroker, Sub};
+        use crate::{Add, LinComb, Recorder, Sub};
+        use aura_strategy::Bias;
+        use aura_backtest::SimBroker;
         use aura_core::{Firing, ScalarKind};
 
         // the load-bearing payoff: two SMAs disambiguate by window
@@ -221,7 +223,9 @@ mod tests {
 
     #[test]
     fn nodes_declare_expected_params() {
-        use crate::{Add, Bias, LinComb, Recorder, SimBroker, Sub};
+        use crate::{Add, LinComb, Recorder, Sub};
+        use aura_strategy::Bias;
+        use aura_backtest::SimBroker;
         use aura_core::{Firing, ParamSpec, ScalarKind};
         // single scalar knobs (declared on the param-generic builder, pre-build)
         assert_eq!(

crates/aura-strategy/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "aura-strategy"
+edition.workspace = true
+version.workspace = true
+license.workspace = true
+publish.workspace = true
+
+[dependencies]
+aura-core = { path = "../aura-core" }

crates/aura-strategy/src/cost.rs

@@ -91,7 +91,7 @@ pub enum ChargeMode {
 ///
 /// ```
 /// use aura_core::Ctx;
-/// use aura_std::{CostNode, CostRunner};
+/// use aura_strategy::{CostNode, CostRunner};
 ///
 /// pub struct HalfSpreadCost {
 ///     half_spread: f64,

crates/aura-strategy/src/lib.rs

@@ -0,0 +1,28 @@
+//! `aura-strategy` — the strategy-definition node layer (C28): bias, stop rules,
+//! sizing, and the cost-model machinery (measured in R). Depends only on
+//! `aura-core`.
+
+mod bias;
+mod carry_cost;
+mod constant_cost;
+mod cost;
+mod cost_sum;
+mod longonly;
+mod sizer;
+mod stop_rule;
+mod vol_slippage_cost;
+mod vol_tf_stop;
+
+pub use bias::Bias;
+pub use carry_cost::CarryCost;
+pub use constant_cost::ConstantCost;
+pub use cost::{
+    cost_node_builder, cost_port, intern_port, ChargeMode, CostNode, CostRunner,
+    COST_FIELD_NAMES, COST_WIDTH, GEOMETRY_WIDTH,
+};
+pub use cost_sum::CostSum;
+pub use longonly::LongOnly;
+pub use sizer::Sizer;
+pub use stop_rule::FixedStop;
+pub use vol_slippage_cost::VolSlippageCost;
+pub use vol_tf_stop::VolTfStop;

crates/aura-vocabulary/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "aura-vocabulary"
+edition.workspace = true
+version.workspace = true
+license.workspace = true
+publish.workspace = true
+
+[dependencies]
+aura-core = { path = "../aura-core" }
+aura-std = { path = "../aura-std" }
+aura-market = { path = "../aura-market" }
+aura-strategy = { path = "../aura-strategy" }
+aura-backtest = { path = "../aura-backtest" }
+
+[dev-dependencies]
+toml = "0.8"

crates/aura-vocabulary/src/lib.rs

@@ -1,10 +1,10 @@
 //! The closed, compiled-in dispatch from a serialized node **type identity** to
-//! its `aura-std` builder factory — the load-side counterpart to the type label
+//! its node-crate builder factory — the load-side counterpart to the type label
 //! a blueprint serializes (`PrimitiveBuilder::label`). This is **not** a dynamic
 //! registry (domain invariant 9): it is a `match` the crate that *owns* the
 //! nodes writes, over its own closed, compiled-in vocabulary (C24 — nodes are
 //! referenced "by compiled-in type identity", never a by-name marketplace). The
-//! engine cannot hold this table (it does not depend on `aura-std`); a loader
+//! engine cannot hold this table (it does not depend on the node crates); a loader
 //! takes it as an injected resolver, and a project `cdylib` later supplies its
 //! own (C16) through the same seam.
 //!
@@ -17,11 +17,13 @@
 //! rather than guessing. Serialising structural-axis construction args is a
 //! later, additive extension (#156/C20).
 
-use crate::{
-    Abs, Add, And, Bias, CarryCost, Const, ConstantCost, CumSum, Delay, Div, Ema, EqConst,
-    FixedStop, Gt, Latch, LongOnly, Max, Min, Mul, PositionManagement, Resample, RollingMax,
-    RollingMin, Scale, Select, SessionFrankfurt, Sign, Sizer, Sma, Sqrt, Sub, VolSlippageCost, When,
+use aura_backtest::PositionManagement;
+use aura_market::{Resample, SessionFrankfurt};
+use aura_std::{
+    Abs, Add, And, Const, CumSum, Delay, Div, Ema, EqConst, Gt, Latch, Max, Min, Mul, RollingMax,
+    RollingMin, Scale, Select, Sign, Sma, Sqrt, Sub, When,
 };
+use aura_strategy::{Bias, CarryCost, ConstantCost, FixedStop, LongOnly, Sizer, VolSlippageCost};
 use aura_core::PrimitiveBuilder;
 
 /// The single roster source (#160): one `"TypeId" => Type` line per zero-arg
@@ -37,7 +39,7 @@ macro_rules! std_vocabulary_roster {
     ($($type_id:literal => $ty:ty),+ $(,)?) => {
         /// Resolve a serialized node type identity (the `PrimitiveBuilder::label`,
         /// e.g. `"SMA"`) to a fresh, unbound builder from the node's own factory.
-        /// Returns `None` for any identity outside the zero-arg `aura-std`
+        /// Returns `None` for any identity outside the zero-arg node
         /// vocabulary.
         pub fn std_vocabulary(type_id: &str) -> Option<PrimitiveBuilder> {
             Some(match type_id {

crates/aura-vocabulary/tests/c28_layering.rs

@@ -0,0 +1,62 @@
+//! C28 structural fitness: the node crates obey the ladder import direction.
+//! The compiler only rejects import cycles; an acyclic-but-outward dependency
+//! (e.g. `aura-std` -> `aura-market`) would compile silently. This test reads
+//! each node crate's `[dependencies]` table and asserts its intra-workspace edges
+//! stay within the inner set C28 permits for that layer. `[dev-dependencies]` are
+//! C28-exempt (tests may cross layers) and are deliberately not inspected.
+
+use std::path::PathBuf;
+
+fn workspace_root() -> PathBuf {
+    // aura-vocabulary/ + /../.. = workspace root (the repo idiom for reaching it).
+    PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("..").join("..")
+}
+
+/// The `aura-*` keys under `[dependencies]` (NOT `[dev-dependencies]`) of a crate.
+fn prod_intra_workspace_deps(crate_name: &str) -> Vec<String> {
+    let manifest = workspace_root()
+        .join("crates")
+        .join(crate_name)
+        .join("Cargo.toml");
+    let text = std::fs::read_to_string(&manifest)
+        .unwrap_or_else(|e| panic!("read {}: {e}", manifest.display()));
+    let doc: toml::Value = toml::from_str(&text).expect("Cargo.toml parses as TOML");
+    match doc.get("dependencies").and_then(|d| d.as_table()) {
+        Some(deps) => deps
+            .keys()
+            .filter(|k| k.starts_with("aura-"))
+            .cloned()
+            .collect(),
+        None => Vec::new(),
+    }
+}
+
+#[test]
+fn node_crates_obey_the_c28_import_direction() {
+    // (crate, the intra-workspace [dependencies] C28 permits for its layer)
+    let allowed: &[(&str, &[&str])] = &[
+        ("aura-std", &["aura-core"]),      // engine
+        ("aura-market", &["aura-core"]),   // market
+        ("aura-strategy", &["aura-core"]), // strategy
+        ("aura-backtest", &["aura-core"]), // backtest (may gain aura-strategy when it imports one)
+        (
+            "aura-vocabulary",
+            &[
+                "aura-core",
+                "aura-std",
+                "aura-market",
+                "aura-strategy",
+                "aura-backtest",
+            ],
+        ),
+    ];
+    for (crate_name, permitted) in allowed {
+        for dep in prod_intra_workspace_deps(crate_name) {
+            assert!(
+                permitted.contains(&dep.as_str()),
+                "C28 import-direction violation: `{crate_name}` [dependencies] on `{dep}`, \
+                 outside its permitted inner set {permitted:?}"
+            );
+        }
+    }
+}

docs/design/INDEX.md

@@ -2684,23 +2684,29 @@ cleanly by layer, so the layering is realized only partially:
   The stratification supplies the *second* metric consumer (measurement) that the
   deferral was waiting on, so retiring #147 and cutting this edge are one coupled
   decision — reserved to the user, since it reverses a ratified deferral.
-- The interweaving is mostly *inside* crates. `aura-std` holds four layers in one
-  roster: engine (arithmetic/logic/rolling + the generic sinks), market
-  (`session.rs`, `resample.rs`), strategy (`bias.rs`/`stop_rule.rs`/`sizer.rs` +
-  the cost nodes) and backtest (`sim_broker.rs`, `position_management.rs`);
-  `aura-analysis` holds backtest reductions and generic hurdle math together. 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.
+- 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 remaining in-crate
+  interweave is `aura-analysis`, which still holds backtest reductions and generic
+  hurdle math together (phase 5). 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 → analysis` edge — coupled to the #147 decision above; (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; (5) split `aura-analysis` into generic statistics and
-  backtest metrics; (6) generify the column's metric interface (demand-driven —
-  this is #147). Crate names provisional; full evidence on #286 and the milestone.
+  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; (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.
 
 ---