docs: open patterns run when the harness can bind them; README's tenth op; C29 backstop

Fieldtest truth pass (composites-use, B1/S1/S2/S3):

- The "running an open pattern standalone refuses" sentence was wrong — and
  it was this cycle's own ratification prose, not code. Reality (ratified
  as-is): the harness binds input roles to archive columns BY NAME (C26), so
  an open pattern whose roles match the data runs standalone as a matter of
  design; what refuses, by name, is a role the harness cannot bind, or the
  run surface's other gates (bias/tap, free knobs). The authoring guide's
  input row now states exactly that; C24's input row ("only compile/
  bootstrap require it bound") and the glossary's "requires them bound"
  were already accurate and stand.
- README enumerated nine op kinds — the tenth (use) added (S2).
- The use-seam C29 doc gate is stated as what it is: a backstop — the
  register verb already gates both input forms, so it fires only for store
  content written before C29 or through the raw in-crate path (S3,
  ratified).

B1's fieldtest classification was bug->debug; overridden to ratify+document:
the observed behaviour is C26-coherent and useful (quick-testing a pattern
against real data), the defect was the sentence. Minuted on #317.

refs #317, refs #339

README.md

@@ -119,9 +119,10 @@ aura sweep crossover.bp.json --list-axes
 ```
 
 The op kinds are `source`, `input`, `add`, `feed`, `connect`, `expose`, `tap`,
-`gang`, and `doc` (`tap` declares a recorded measurement point on an interior
+`gang`, `doc`, and `use` (`tap` declares a recorded measurement point on an
-wire; `doc` declares the composite's one-line meaning, required at register —
+interior wire; `doc` declares the composite's one-line meaning, required at
-C29; see the authoring guide). See
+register — C29; `use` splices a registered blueprint in as a nested composite,
+by content id or label; see the authoring guide). See
 `aura graph introspect --node <T>` for a type's exact ports and the op-script
 grammar in the design ledger for the full semantics.
 

crates/aura-cli/src/graph_construct.rs

@@ -9,16 +9,18 @@ use std::path::Path;
 
 use aura_engine::{
     blueprint_from_json, blueprint_identity_json, blueprint_to_json, replay, BindOpError,
-    CompileError, Composite, GraphSession, LoadError, Op, OpError, Scalar, ScalarKind,
+    BlueprintDoc, CompileError, Composite, GraphSession, LoadError, Op, OpError, Scalar, ScalarKind,
 };
 use serde::Deserialize;
 
+use crate::research_docs::resolve_id_prefix;
+
 // `std_vocabulary` is now only reached through `aura_runner::project::Env::resolve` in
 // production code; tests still exercise it directly.
 #[cfg(test)]
 use aura_vocabulary::std_vocabulary;
 
-/// The op-list reference `aura graph build --help` appends (#323): the nine
+/// The op-list reference `aura graph build --help` appends (#323): the ten
 /// op kinds with their fields and one worked element each. Lives beside
 /// [`OpDoc`] so a new op variant is one screen away from its help line.
 pub const OP_REFERENCE: &str = r#"Op-list reference (stdin: a JSON array of op objects, applied in order):
@@ -40,6 +42,9 @@ pub const OP_REFERENCE: &str = r#"Op-list reference (stdin: a JSON array of op o
       fuse two or more sibling params into one public knob
   {"op":"doc","text":"..."}
       declare the composite's one-line meaning (C29)
+  {"op":"use","ref":{"name":"agree"},"name":"gate","bind":{"sma.length":{"I64":9}}}
+      splice a registered blueprint (by "content_id" or "name") under an
+      instance name ("bind" path-qualifies the spliced instance's params)
 
 Node types and their ports: aura graph introspect --vocabulary | --node <T>"#;
 
@@ -82,26 +87,66 @@ enum OpDoc {
     /// Declare the composite's one-line meaning (C29, #316) — the op-script
     /// twin of the builder's `.doc(...)`.
     Doc { text: String },
+    /// Splice a registered blueprint into the building graph as a nested
+    /// composite (#317) — the DTO the engine's `Op::Use` never sees
+    /// directly: the CLI resolves `ref` (a store content id, a unique
+    /// content-id prefix, or a registry name label) to the full content id
+    /// at conversion time, before the engine ever runs.
+    Use {
+        #[serde(rename = "ref")]
+        r#ref: UseRef,
+        #[serde(default)]
+        name: Option<String>,
+        #[serde(default)]
+        bind: BTreeMap<String, Scalar>,
+    },
+}
+
+/// A `use` op's reference (#317) — exactly one of a store content id (full
+/// or a unique prefix, #302 semantics) or a registry name label
+/// (`graph register --name`, latest-wins).
+#[derive(Debug, Deserialize)]
+#[serde(deny_unknown_fields)]
+enum UseRef {
+    #[serde(rename = "content_id")]
+    ContentId(String),
+    #[serde(rename = "name")]
+    Name(String),
 }
 
 impl OpDoc {
-    /// The op-kind label for the `op N (kind): cause` message.
+    /// The op-kind label for the `op N (kind): cause` message. A `use` op
-    fn kind_label(&self) -> &'static str {
+    /// carries its instance name (when the author gave one) so a `use`
+    /// fault reads `use "gate"`, not a bare, undifferentiated `use` — the
+    /// only kind whose label is not a fixed string (#317).
+    fn kind_label(&self) -> String {
         match self {
-            OpDoc::Source { .. } => "source",
+            OpDoc::Source { .. } => "source".to_string(),
-            OpDoc::Input { .. } => "input",
+            OpDoc::Input { .. } => "input".to_string(),
-            OpDoc::Add { .. } => "add",
+            OpDoc::Add { .. } => "add".to_string(),
-            OpDoc::Feed { .. } => "feed",
+            OpDoc::Feed { .. } => "feed".to_string(),
-            OpDoc::Connect { .. } => "connect",
+            OpDoc::Connect { .. } => "connect".to_string(),
-            OpDoc::Expose { .. } => "expose",
+            OpDoc::Expose { .. } => "expose".to_string(),
-            OpDoc::Tap { .. } => "tap",
+            OpDoc::Tap { .. } => "tap".to_string(),
-            OpDoc::Gang { .. } => "gang",
+            OpDoc::Gang { .. } => "gang".to_string(),
-            OpDoc::Doc { .. } => "doc",
+            OpDoc::Doc { .. } => "doc".to_string(),
+            OpDoc::Use { name: Some(n), .. } => format!("use {n:?}"),
+            OpDoc::Use { name: None, .. } => "use".to_string(),
         }
     }
 }
 
 impl From<OpDoc> for Op {
+    /// Infallible, context-free conversion — used directly only by
+    /// build-free introspection paths (`introspect --unwired`, #317's
+    /// spec: "Build-free introspection paths pass a `|_| None` closure"),
+    /// which never resolve a `use` ref through the registry. A bare
+    /// `OpDoc::Use` therefore maps its `UseRef` payload verbatim into
+    /// `ref_id` (unresolved) — that session's `subgraph` closure is always
+    /// `&|_| None`, so any `use` op there faults `UnknownSubgraph`
+    /// regardless of the exact `ref_id` text; `graph build`'s real path
+    /// (`composite_from_str`) never reaches this arm — it resolves and
+    /// replaces each `Op::Use` before conversion (see `resolve_use_op`).
     fn from(d: OpDoc) -> Op {
         match d {
             OpDoc::Source { role, kind } => Op::Source { role, kind },
@@ -115,6 +160,14 @@ impl From<OpDoc> for Op {
             OpDoc::Tap { from, as_name } => Op::Tap { from, as_name },
             OpDoc::Gang { as_name, into } => Op::Gang { as_name, into },
             OpDoc::Doc { text } => Op::Doc { text },
+            OpDoc::Use { r#ref, name, bind } => Op::Use {
+                ref_id: match r#ref {
+                    UseRef::ContentId(id) => id,
+                    UseRef::Name(name) => name,
+                },
+                name,
+                bind: bind.into_iter().collect(),
+            },
         }
     }
 }
@@ -147,10 +200,12 @@ fn format_op_error(e: &OpError) -> String {
             BindOpError::KindMismatch { param, expected, got } => {
                 format!("param {node}.{param} expects {expected:?} but got {got:?}")
             }
+            BindOpError::AlreadyGanged { param, gang } => {
+                format!("cannot bind {node}.{param} — member of gang {gang:?}")
+            }
         },
         OpError::UnconnectedPort { node, slot } => format!("slot {node}.{slot} is unconnected"),
         OpError::RoleKindMismatch { role } => format!("input role {role} fans into slots of differing kinds"),
-        OpError::UnboundRootRole { role } => format!("root input role {role} is unbound"),
         OpError::GangKindMismatch { member, expected, got } => {
             format!("gang: member `{member}` is {got:?}, expected {expected:?}")
         }
@@ -160,18 +215,174 @@ fn format_op_error(e: &OpError) -> String {
         OpError::GangArity { gang } => format!("gang `{gang}`: needs at least two members"),
         OpError::Incomplete(ce) => format!("{ce:?}"),
         OpError::DuplicateDoc => "a doc op may appear at most once".to_string(),
+        // #317: `graph build`'s real path (`composite_from_str`) resolves and
+        // fetches every `use` op before replay, so this never fires there —
+        // but `introspect --unwired` stays build-free/subgraph-free by spec
+        // (`&|_| None`, see `From<OpDoc> for Op`), so a `use` op in a partial
+        // document reaches this arm through THAT path, by-identifier on the
+        // (unresolved) `ref_id` text.
+        OpError::UnknownSubgraph { ref_id } => {
+            format!("use: no subgraph for content id {ref_id:?}")
         }
     }
+}
+
+/// Resolve one `use` op's [`UseRef`] to the full store content id (#317):
+/// verbatim if it already IS a 64-hex content id, else a unique content-id
+/// prefix (#302 semantics, reusing [`resolve_id_prefix`]) or a registry name
+/// label (latest-wins, [`aura_registry::Registry::resolve_blueprint_label`]).
+/// Returns the full id plus the `<label-or-prefix> -> <full id>` text the
+/// resolution echo shows — the bare cause on a miss (unknown label / unknown
+/// or ambiguous prefix), for the caller to attribute by op index.
+fn resolve_use_ref_id(r: &UseRef, registry: &aura_registry::Registry) -> Result<(String, String), String> {
+    match r {
+        UseRef::Name(label) => {
+            let id = registry.resolve_blueprint_label(label).ok_or_else(|| {
+                let labels = registry.blueprint_labels();
+                if labels.is_empty() {
+                    format!("no registered blueprint labeled {label:?} — no labels registered")
+                } else {
+                    let names = labels.iter().map(|(n, _)| n.as_str()).collect::<Vec<_>>().join(", ");
+                    format!("no registered blueprint labeled {label:?} — registered labels: {names}")
+                }
+            })?;
+            Ok((id.clone(), format!("{label} -> {id}")))
+        }
+        UseRef::ContentId(raw) => {
+            if aura_runner::axes::is_content_id(raw) {
+                return Ok((raw.clone(), format!("{raw} -> {raw}")));
+            }
+            let candidates = registry.list_blueprint_ids().map_err(|e| e.to_string())?;
+            match resolve_id_prefix(raw, &candidates)? {
+                Some(full) => {
+                    let shown = format!("{raw} -> {full}");
+                    Ok((full, shown))
+                }
+                None => Err(format!("no registered blueprint matches content id {raw:?}")),
+            }
+        }
+    }
+}
+
+/// The 12-char content-id prefix convention `graph introspect --registered`
+/// shows (#317), reused in the use-seam C29 refusal so both surfaces name a
+/// blueprint the same shortened way.
+fn id_prefix12(id: &str) -> &str {
+    &id[..id.len().min(12)]
+}
+
+/// The use-seam C29 doc-gate refusal cause (#317): re-run
+/// [`aura_registry::gate_composite_docs`] — the SAME walk `graph register`
+/// gates the write path with — over a FETCHED composite, before it ever
+/// reaches the session; names the fetched blueprint's id-prefix and the
+/// failing (root or nested — from the consumer's view, everything fetched is
+/// "nested") composite by identifier, mirroring `research_docs.rs`'s
+/// `BadDescription` phrasing for the same two `DocGateFault` kinds.
+fn use_doc_gate_cause(full_id: &str, e: &aura_registry::RegistryError) -> String {
+    let aura_registry::RegistryError::UndescribedComposite { name, fault } = e else {
+        // Defensive: `gate_composite_docs` only ever constructs
+        // `UndescribedComposite`; every other `RegistryError` variant is
+        // unreachable from this call, but the match stays total rather than
+        // panicking on a surprise variant.
+        return format!("registered blueprint {} fails the description gate", id_prefix12(full_id));
+    };
+    let rule = match fault {
+        aura_core::DocGateFault::Empty => format!(
+            "nested composite {name:?} has no description — re-register it with a \"doc\" op (C29)"
+        ),
+        aura_core::DocGateFault::RestatesName => {
+            format!("nested composite {name:?} has a doc that merely restates its name (C29)")
+        }
+    };
+    format!("registered blueprint {} fails the description gate: {rule}", id_prefix12(full_id))
+}
+
+/// Resolve, fetch, C29-gate, and echo one `use` op (#317) — the CLI-side
+/// half of the store/engine split (the engine never resolves a label, a
+/// prefix, or the registry itself). On success, caches the fetched
+/// CANONICAL JSON (not the parsed `Composite` — `Composite` is not `Clone`,
+/// mirroring the engine's own `use_fixture`-reload test pattern) under the
+/// full content id, so the `subgraph` closure handed to `replay` is a pure,
+/// registry-free lookup that re-parses on every call. Returns the bare
+/// cause on any refusal; the caller attributes it by op index.
+fn resolve_use_op(
+    r#ref: UseRef,
+    name: Option<String>,
+    bind: BTreeMap<String, Scalar>,
+    env: &aura_runner::project::Env,
+    cache: &mut std::collections::HashMap<String, String>,
+) -> Result<Op, String> {
+    let registry = env.registry();
+    let (full_id, shown) = resolve_use_ref_id(&r#ref, &registry)?;
+    let json = registry
+        .get_blueprint(&full_id)
+        .map_err(|e| e.to_string())?
+        .ok_or_else(|| format!("no registered blueprint {full_id}"))?;
+    let doc: BlueprintDoc = serde_json::from_str(&json)
+        .map_err(|e| format!("registered blueprint {full_id} is not a valid blueprint: {e}"))?;
+    // C29 at the use seam: gate the DATA form (no vocabulary needed) before
+    // the composite ever reaches the session.
+    if let Err(e) = aura_registry::gate_composite_docs(&doc.blueprint) {
+        return Err(use_doc_gate_cause(&full_id, &e));
+    }
+    // Resolve the fetched envelope through the FULL vocabulary here, at DTO
+    // conversion (review finding, #317 follow-up): deferring this to the
+    // `subgraph` closure's lazy re-parse let a deserialize/vocab-resolution
+    // failure fold into `.ok() -> None`, which `replay` then misreports as
+    // `UnknownSubgraph` — a fetched-but-unloadable blueprint is a runtime
+    // content fault (exit 1), not a missing reference. `blueprint_load_prose`
+    // + `unresolved_namespace_hint` are the same house-style pair
+    // `blueprint_slot_prose`/`composite_from_any` already use over a
+    // `LoadError`.
+    if let Err(e) = blueprint_from_json(&json, &|t| env.resolve(t)) {
+        let mut msg = blueprint_load_prose(&e);
+        if let Some(hint) = unresolved_namespace_hint(&e, env) {
+            msg.push_str(" — ");
+            msg.push_str(&hint);
+        }
+        return Err(format!("registered blueprint {} is invalid: {msg}", id_prefix12(&full_id)));
+    }
+    let instance = name.clone().unwrap_or_else(|| doc.blueprint.name.clone());
+    // The resolution echo (C14 benign class): stderr only, so stdout stays
+    // clean payload (#164's convention, extended to this new note).
+    crate::diag::note!("use {instance:?}: {shown}");
+    cache.insert(full_id.clone(), json);
+    Ok(Op::Use { ref_id: full_id, name, bind: bind.into_iter().collect() })
+}
 
 /// Parse a JSON op-list document and replay it through the env's vocabulary into
 /// a built `Composite` — or a `op N (kind): cause` message (a per-op fault,
 /// attributed by the retained op-kind list) / `finalize: cause` (a holistic fault
-/// past the last op).
+/// past the last op). Every `use` op resolves through the registry HERE, before
+/// replay (#317): a resolution/doc-gate fault is attributed exactly like any
+/// other per-op construction fault (same `op N (kind): cause` shape, exit 1).
 fn composite_from_str(doc: &str, env: &aura_runner::project::Env) -> Result<Composite, String> {
     let docs: Vec<OpDoc> = serde_json::from_str(doc).map_err(|e| format!("invalid op-list: {e}"))?;
-    let labels: Vec<&'static str> = docs.iter().map(OpDoc::kind_label).collect();
+    let labels: Vec<String> = docs.iter().map(OpDoc::kind_label).collect();
-    let ops: Vec<Op> = docs.into_iter().map(Op::from).collect();
+    let mut cache: std::collections::HashMap<String, String> = std::collections::HashMap::new();
-    replay("graph", ops, &|t| env.resolve(t)).map_err(|(idx, err)| {
+    let mut ops: Vec<Op> = Vec::with_capacity(docs.len());
+    for (idx, d) in docs.into_iter().enumerate() {
+        let op = match d {
+            OpDoc::Use { r#ref, name, bind } => match resolve_use_op(r#ref, name, bind, env, &mut cache) {
+                Ok(op) => op,
+                Err(cause) => return Err(format!("op {idx} ({}): {cause}", labels[idx])),
+            },
+            other => Op::from(other),
+        };
+        ops.push(op);
+    }
+    // The injected `subgraph` lookup (#317): a pure, registry-free map read —
+    // every `use` op's blueprint was already fetched, gated, AND resolved
+    // (`resolve_use_op`'s eager `blueprint_from_json` check) above; this
+    // closure only re-parses the cached bytes (`Composite` is not `Clone`).
+    // The `.ok()` is defensive, not a fallible path in practice: re-parsing
+    // the SAME cached JSON through the SAME pure resolver cannot fail here
+    // once it has already succeeded once above (review finding, #317
+    // follow-up — the failure case now surfaces eagerly, at DTO conversion).
+    let subgraph = |ref_id: &str| {
+        cache.get(ref_id).and_then(|json| blueprint_from_json(json, &|t| env.resolve(t)).ok())
+    };
+    replay("graph", ops, &|t| env.resolve(t), &subgraph).map_err(|(idx, err)| {
         let mut cause = format_op_error(&err);
         // #244: the op-script path reports an unresolvable namespaced type as
         // `OpError::UnknownNodeType`, a different error family than the
@@ -245,7 +456,11 @@ pub fn introspect_node(type_id: &str, env: &aura_runner::project::Env) -> Result
 pub fn introspect_unwired(doc: &str, env: &aura_runner::project::Env) -> Result<String, String> {
     let docs: Vec<OpDoc> = serde_json::from_str(doc).map_err(|e| format!("invalid op-list: {e}"))?;
     let resolver = |t: &str| env.resolve(t);
-    let mut session = GraphSession::new("introspect", &resolver);
+    // #317: build-free introspection stays subgraph-free by design (spec:
+    // "Build-free introspection paths pass a `|_| None` closure") — a `use`
+    // op here always misses (`OpError::UnknownSubgraph`, `From<OpDoc>`'s own
+    // doc comment), never a registry read.
+    let mut session = GraphSession::new("introspect", &resolver, &|_: &str| None);
     for (i, d) in docs.into_iter().enumerate() {
         session.apply(Op::from(d)).map_err(|e| format!("op {i}: {}", format_op_error(&e)))?;
     }
@@ -256,6 +471,33 @@ pub fn introspect_unwired(doc: &str, env: &aura_runner::project::Env) -> Result<
     Ok(out)
 }
 
+/// `aura graph introspect --registered` (#317): one row per registry label —
+/// `<label>  <12-char id prefix>  <root doc line>`, latest-wins (the label
+/// sidecar's own resolution rule) — the discovery surface the worked
+/// acceptance program's last step reads. An empty store is `no labels
+/// registered` on stdout, exit 0 (a listing, not a fault); dangling label
+/// rows (content id no longer resolves) are already skipped by
+/// `blueprint_labels()`.
+fn introspect_registered(env: &aura_runner::project::Env) -> Result<String, String> {
+    let registry = env.registry();
+    let labels = registry.blueprint_labels();
+    if labels.is_empty() {
+        return Ok("no labels registered\n".to_string());
+    }
+    let mut out = String::new();
+    for (name, id) in labels {
+        let json = registry
+            .get_blueprint(&id)
+            .map_err(|e| e.to_string())?
+            .ok_or_else(|| format!("label {name:?} names {id}, which is not in the store"))?;
+        let doc: BlueprintDoc = serde_json::from_str(&json)
+            .map_err(|e| format!("registered blueprint {id} is not a valid blueprint: {e}"))?;
+        let root_doc = doc.blueprint.doc.as_deref().unwrap_or("");
+        out.push_str(&format!("{name}  {}  {root_doc}\n", id_prefix12(&id)));
+    }
+    Ok(out)
+}
+
 /// `aura graph introspect`: dispatch the read-only queries. Exactly one of
 /// `--vocabulary` / `--node <T>` / `--unwired` / `--params <FILE|ID>` / the id
 /// group must be set; zero or more than one is the usage error (exit 2). The id
@@ -266,11 +508,12 @@ pub fn introspect_cmd(cmd: crate::GraphIntrospectCmd, env: &aura_runner::project
         + cmd.node.is_some() as usize
         + cmd.unwired as usize
         + cmd.folds as usize
+        + cmd.registered as usize
         + cmd.params.is_some() as usize
         + (cmd.content_id.is_some() || cmd.identity_id) as usize;
     if count != 1 {
         eprintln!(
-            "aura: Usage: aura graph introspect --vocabulary | --node <T> | --unwired | --folds | --params <FILE|ID> | --content-id [FILE] | --identity-id (the two id flags may be combined)"
+            "aura: Usage: aura graph introspect --vocabulary | --node <T> | --unwired | --folds | --registered | --params <FILE|ID> | --content-id [FILE] | --identity-id (the two id flags may be combined)"
         );
         std::process::exit(2);
     }
@@ -294,6 +537,17 @@ pub fn introspect_cmd(cmd: crate::GraphIntrospectCmd, env: &aura_runner::project
         for (label, doc) in aura_runner::FoldRegistry::core().roster() {
             println!("{label:<7} — {doc}");
         }
+    } else if cmd.registered {
+        // The label sidecar's discovery surface (#317): one row per
+        // registered label — nothing to build, so a store-only read, exit 0
+        // even on an empty store (a listing, not a fault).
+        match introspect_registered(env) {
+            Ok(s) => print!("{s}"),
+            Err(m) => {
+                eprintln!("aura: {m}");
+                std::process::exit(1);
+            }
+        }
     } else if let Some(type_id) = cmd.node.as_deref() {
         match introspect_node(type_id, env) {
             Ok(s) => print!("{s}"),
@@ -580,13 +834,20 @@ fn params_lines(target: &str, env: &aura_runner::project::Env) -> Result<String,
     Ok(out)
 }
 
-/// `aura graph register <blueprint.json>` (#196): parse the blueprint through
+/// `aura graph register <blueprint.json> [--name <label>]` (#196, `--name`
-/// the project vocabulary, canonicalize, content-address, and store — the
+/// #317): parse the blueprint through the project vocabulary, canonicalize,
-/// `process register` pattern, printing the store path so the trail is
+/// content-address, and store — the `process register` pattern, printing
-/// followable. Prose to stderr + exit 1 on any refusal.
+/// the store path so the trail is followable. With `--name`, additionally
-pub fn register_cmd(file: &Path, env: &aura_runner::project::Env) {
+/// labels the stored content id (`aura_registry::Registry::put_blueprint_label`),
-    match register_blueprint(file, env) {
+/// echoing the repoint when the label already pointed elsewhere. Prose to
-        Ok(line) => println!("{line}"),
+/// stderr + exit 1 on any refusal.
+pub fn register_cmd(file: &Path, name: Option<&str>, env: &aura_runner::project::Env) {
+    match register_blueprint(file, name, env) {
+        Ok(lines) => {
+            for line in lines {
+                println!("{line}");
+            }
+        }
         Err(m) => {
             eprintln!("aura: {m}");
             std::process::exit(1);
@@ -594,7 +855,11 @@ pub fn register_cmd(file: &Path, env: &aura_runner::project::Env) {
     }
 }
 
-fn register_blueprint(file: &Path, env: &aura_runner::project::Env) -> Result<String, String> {
+fn register_blueprint(
+    file: &Path,
+    name: Option<&str>,
+    env: &aura_runner::project::Env,
+) -> Result<Vec<String>, String> {
     let text = std::fs::read_to_string(file)
         .map_err(|e| format!("cannot read {}: {e}", file.display()))?;
     // Shape-discriminated like file-mode --content-id (#202): either shape
@@ -604,10 +869,21 @@ fn register_blueprint(file: &Path, env: &aura_runner::project::Env) -> Result<St
     let id = crate::content_id(&canonical);
     let registry = env.registry();
     registry.put_blueprint(&id, &canonical).map_err(|e| e.to_string())?;
-    Ok(format!(
+    let mut lines = vec![format!(
         "registered blueprint {id} ({})",
         registry.blueprint_path(&id).display()
-    ))
+    )];
+    if let Some(label) = name {
+        // Resolve BEFORE writing, so the repoint echo compares against the
+        // pre-write target (#317).
+        let previous = registry.resolve_blueprint_label(label);
+        registry.put_blueprint_label(label, &id).map_err(|e| e.to_string())?;
+        lines.push(match previous {
+            Some(old) if old != id => format!("label {label:?} -> {id} (was {old})"),
+            _ => format!("label {label:?} -> {id}"),
+        });
+    }
+    Ok(lines)
 }
 
 #[cfg(test)]
@@ -636,7 +912,8 @@ mod tests {
         assert_eq!(docs[1].kind_label(), "add");
         let ops: Vec<Op> = docs.into_iter().map(Op::from).collect();
         // both SMA lengths are bound, so the only open param is bias.scale (f64).
-        let composite = replay("graph", ops, &std_vocabulary).expect("replay resolves");
+        let composite =
+            replay("graph", ops, &std_vocabulary, &|_: &str| None).expect("replay resolves");
         composite.compile_with_params(&[Scalar::f64(0.5)]).expect("compiles");
     }
 

crates/aura-cli/src/main.rs

@@ -1232,6 +1232,10 @@ enum GraphSub {
     Register {
         /// The blueprint .json file to register.
         file: std::path::PathBuf,
+        /// Label the registered content id for `use` by name (#317); a
+        /// re-registered label repoints (latest-wins on resolve).
+        #[arg(long)]
+        name: Option<String>,
     },
 }
 
@@ -1249,6 +1253,9 @@ struct GraphIntrospectCmd {
     /// List the closed tap-fold vocabulary (fold, bind rule, output kind, meaning).
     #[arg(long)]
     folds: bool,
+    /// List every registered blueprint label (#317): label, id prefix, root doc.
+    #[arg(long)]
+    registered: bool,
     /// Print the graph's content id (topology hash). With FILE, read the
     /// document from it (a blueprint envelope or an op-list, shape-
     /// discriminated, #196); without FILE, read a stdin op-list as before.
@@ -1943,7 +1950,7 @@ fn dispatch_graph(a: GraphCmd, env: &aura_runner::project::Env) {
         },
         Some(GraphSub::Build) => graph_construct::build_cmd(env),
         Some(GraphSub::Introspect(i)) => graph_construct::introspect_cmd(i, env),
-        Some(GraphSub::Register { file }) => graph_construct::register_cmd(&file, env),
+        Some(GraphSub::Register { file, name }) => graph_construct::register_cmd(&file, name.as_deref(), env),
     }
 }
 

crates/aura-cli/src/research_docs.rs

@@ -294,7 +294,7 @@ fn register_process(file: &PathBuf, env: &Env) -> Result<(), String> {
 /// caller's existing not-found prose applies unchanged. `Err`: two or more
 /// candidates share the prefix — refused by name, listing every candidate,
 /// rather than guessed.
-fn resolve_id_prefix(prefix: &str, candidates: &[String]) -> Result<Option<String>, String> {
+pub(crate) fn resolve_id_prefix(prefix: &str, candidates: &[String]) -> Result<Option<String>, String> {
     let matches: Vec<&String> = candidates.iter().filter(|c| c.starts_with(prefix)).collect();
     match matches.as_slice() {
         [] => Ok(None),

crates/aura-cli/tests/graph_construct.rs

@@ -466,6 +466,24 @@ fn run_in(dir: &std::path::Path, args: &[&str]) -> (String, String, Option<i32>)
     )
 }
 
+/// Run `aura <args>` in `dir` with `stdin_doc` piped in; return (stderr, exit
+/// code) — the `run_code`/`run_in` cross, for a `use`-seam fault that needs
+/// BOTH a project cwd (the label sidecar lives under `<cwd>/runs/`) and a
+/// piped op-list.
+fn run_code_in(dir: &std::path::Path, args: &[&str], stdin_doc: &str) -> (String, Option<i32>) {
+    let mut child = Command::new(BIN)
+        .args(args)
+        .current_dir(dir)
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .spawn()
+        .expect("spawn aura");
+    child.stdin.take().unwrap().write_all(stdin_doc.as_bytes()).unwrap();
+    let out = child.wait_with_output().expect("wait aura");
+    (String::from_utf8_lossy(&out.stderr).into_owned(), out.status.code())
+}
+
 /// The absolute path of a blueprint fixture shipped with this test crate.
 fn fixture(name: &str) -> String {
     format!("{}/tests/fixtures/{name}", env!("CARGO_MANIFEST_DIR"))
@@ -1551,3 +1569,300 @@ fn tap_authored_via_op_script_runs_and_persists_the_series() {
         assert!((g - e).abs() < 1e-9, "row {i}: got {g}, expected {e}");
     }
 }
+
+// ---- `use` / label sidecar / open patterns (#317) ------------------------
+
+/// A small reusable pattern: an open `x` input role feeds an `SMA`, whose
+/// value re-exports as `out` — the fixture every `use`-seam e2e test below
+/// registers under a label. `sma.length` stays UNBOUND: the pattern's own
+/// open param, so a consumer's `--list-axes` sees the bare (unbound) form.
+const OPEN_PATTERN_DOC: &str = r#"[
+    {"op":"doc","text":"a reusable smoothing pattern"},
+    {"op":"input","role":"x"},
+    {"op":"add","type":"SMA","name":"sma"},
+    {"op":"feed","role":"x","into":["sma.series"]},
+    {"op":"expose","from":"sma.value","as":"out"}
+]"#;
+
+/// Build `doc` via `aura graph build` in `dir` and write the resulting
+/// envelope to `dir/<stem>.bp.json`, returning its path.
+fn build_envelope_in(dir: &std::path::Path, doc: &str, stem: &str) -> std::path::PathBuf {
+    let (bytes, _e, ok) = run(&["graph", "build"], doc);
+    assert!(ok, "the fixture document builds: {doc}");
+    let path = dir.join(format!("{stem}.bp.json"));
+    std::fs::write(&path, &bytes).expect("write built envelope");
+    path
+}
+
+/// `graph register --name` (#317): the label sidecar echo on first
+/// registration, and the repoint echo (`(was <old-id>)`) on a second
+/// registration of DIFFERENT bytes under the SAME label.
+#[test]
+fn graph_register_name_labels_and_repoints() {
+    let dir = temp_cwd("register-name");
+    let bp = build_envelope_in(&dir, OPEN_PATTERN_DOC, "pattern");
+    let (out1, err1, code1) =
+        run_in(&dir, &["graph", "register", bp.to_str().unwrap(), "--name", "smooth"]);
+    assert_eq!(code1, Some(0), "first register --name: {out1} {err1}");
+    let id1 = registered_id(&out1);
+    assert!(
+        out1.lines().any(|l| l == format!("label \"smooth\" -> {id1}")),
+        "the plain label echo (no repoint on a fresh label): {out1}"
+    );
+
+    // Different bytes (a bound sma.length), same label -> a repoint.
+    let doc2 = OPEN_PATTERN_DOC.replace(
+        r#"{"op":"add","type":"SMA","name":"sma"}"#,
+        r#"{"op":"add","type":"SMA","name":"sma","bind":{"length":{"I64":7}}}"#,
+    );
+    let bp2 = build_envelope_in(&dir, &doc2, "pattern2");
+    let (out2, err2, code2) =
+        run_in(&dir, &["graph", "register", bp2.to_str().unwrap(), "--name", "smooth"]);
+    assert_eq!(code2, Some(0), "second register --name: {out2} {err2}");
+    let id2 = registered_id(&out2);
+    assert_ne!(id1, id2, "the two registrations are distinct content");
+    assert!(
+        out2.lines().any(|l| l == format!("label \"smooth\" -> {id2} (was {id1})")),
+        "the repoint echo names both ids: {out2}"
+    );
+}
+
+/// `use` resolves a registry label (#317): the resolution echo lands on
+/// STDERR (`aura: note: use "<instance>": <label> -> <full id>`), stdout
+/// stays clean payload — the existing e2e convention this cycle extends.
+#[test]
+fn graph_build_use_resolves_a_label_and_echoes_the_id() {
+    let dir = temp_cwd("use-resolves-label");
+    let bp = build_envelope_in(&dir, OPEN_PATTERN_DOC, "pattern");
+    let (reg_out, reg_err, reg_code) =
+        run_in(&dir, &["graph", "register", bp.to_str().unwrap(), "--name", "smooth"]);
+    assert_eq!(reg_code, Some(0), "register --name: {reg_out} {reg_err}");
+    let id = registered_id(&reg_out);
+
+    let consumer = r#"[
+        {"op":"source","role":"price","kind":"F64"},
+        {"op":"use","ref":{"name":"smooth"},"name":"trend"},
+        {"op":"feed","role":"price","into":["trend.x"]},
+        {"op":"expose","from":"trend.out","as":"bias"}
+    ]"#;
+    let mut child = Command::new(BIN)
+        .args(["graph", "build"])
+        .current_dir(&dir)
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .spawn()
+        .expect("spawn aura graph build");
+    child.stdin.take().unwrap().write_all(consumer.as_bytes()).unwrap();
+    let out = child.wait_with_output().expect("wait aura graph build");
+    assert!(out.status.success(), "build succeeds: {}", String::from_utf8_lossy(&out.stderr));
+    let stdout = String::from_utf8_lossy(&out.stdout);
+    let stderr = String::from_utf8_lossy(&out.stderr);
+    assert_eq!(
+        stderr.trim(),
+        format!("aura: note: use \"trend\": smooth -> {id}"),
+        "the resolution echo names the instance, the label, and the full id: {stderr}"
+    );
+    assert!(stdout.starts_with('{'), "stdout stays clean blueprint payload: {stdout}");
+    assert!(!stdout.contains("aura: note:"), "the note never leaks onto stdout: {stdout}");
+    assert!(
+        stdout.contains(&format!("\"doc\":\"{}\"", "a reusable smoothing pattern")),
+        "the spliced instance's own doc survives inline: {stdout}"
+    );
+}
+
+/// An unknown `use` label enumerates every registered label (C29's "name the
+/// closed set" idiom) and refuses at exit 1 (op-list content fault, #175).
+#[test]
+fn graph_build_use_unknown_label_enumerates_labels_exit_1() {
+    let dir = temp_cwd("use-unknown-label");
+    let bp = build_envelope_in(&dir, OPEN_PATTERN_DOC, "pattern");
+    let (reg_out, reg_err, reg_code) =
+        run_in(&dir, &["graph", "register", bp.to_str().unwrap(), "--name", "smooth"]);
+    assert_eq!(reg_code, Some(0), "register --name: {reg_out} {reg_err}");
+
+    let consumer = r#"[
+        {"op":"source","role":"price","kind":"F64"},
+        {"op":"use","ref":{"name":"nope"},"name":"trend"},
+        {"op":"feed","role":"price","into":["trend.x"]},
+        {"op":"expose","from":"trend.out","as":"bias"}
+    ]"#;
+    let out = std::process::Command::new(BIN)
+        .args(["graph", "build"])
+        .current_dir(&dir)
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .spawn()
+        .and_then(|mut child| {
+            use std::io::Write;
+            child.stdin.take().unwrap().write_all(consumer.as_bytes())?;
+            child.wait_with_output()
+        })
+        .expect("run aura graph build");
+    assert_eq!(out.status.code(), Some(1), "unknown label is a content fault -> exit 1");
+    let stdout = String::from_utf8_lossy(&out.stdout);
+    let stderr = String::from_utf8_lossy(&out.stderr);
+    assert!(stdout.is_empty(), "no blueprint emitted on refusal: {stdout}");
+    assert!(stderr.contains("op 1 (use \"trend\")"), "names the op by index and instance: {stderr}");
+    assert!(stderr.contains("no registered blueprint labeled \"nope\""), "names the miss: {stderr}");
+    assert!(stderr.contains("registered labels: smooth"), "enumerates the closed set: {stderr}");
+}
+
+/// The empty-store form of the unknown-label refusal: no labels to
+/// enumerate reads as prose, not a bare empty list.
+#[test]
+fn graph_build_use_unknown_label_empty_store_reads_as_prose() {
+    let dir = temp_cwd("use-unknown-label-empty-store");
+    let consumer = r#"[
+        {"op":"source","role":"price","kind":"F64"},
+        {"op":"use","ref":{"name":"nope"},"name":"trend"},
+        {"op":"feed","role":"price","into":["trend.x"]},
+        {"op":"expose","from":"trend.out","as":"bias"}
+    ]"#;
+    let (stderr, code) = run_code_in(&dir, &["graph", "build"], consumer);
+    assert_eq!(code, Some(1), "still a content fault -> exit 1");
+    assert!(
+        stderr.contains("no registered blueprint labeled \"nope\" — no labels registered"),
+        "the empty-store form reads as prose: {stderr}"
+    );
+}
+
+/// C29 at the `use` seam (#317): a doc-less registered blueprint refuses
+/// entering a NEW composition, naming the ref's id-prefix, the failing
+/// (here root, "nested" from the consumer's view) composite, and the rule —
+/// exit 1. The doc-less entry reaches the store via the RAW file write
+/// existing pre-C29 fixtures use (`register_refuses_undescribed_composites_
+/// end_to_end`'s technique): `graph register` itself always C29-gates, so a
+/// doc-less entry can only reach the store by writing the file directly.
+#[test]
+fn graph_build_use_docless_source_refuses_with_the_c29_shape_exit_1() {
+    let dir = temp_cwd("use-docless-source");
+    // A doc-less pattern: same shape as OPEN_PATTERN_DOC minus the `doc` op.
+    let docless = r#"[
+        {"op":"input","role":"x"},
+        {"op":"add","type":"SMA","name":"sma","bind":{"length":{"I64":3}}},
+        {"op":"feed","role":"x","into":["sma.series"]},
+        {"op":"expose","from":"sma.value","as":"out"}
+    ]"#;
+    let (envelope, _e, built) = run(&["graph", "build"], docless);
+    assert!(built, "the doc-less pattern still builds (C29 gates register/use, not build)");
+    let (id_out, _e2, id_ok) = run(&["graph", "introspect", "--content-id"], docless);
+    assert!(id_ok, "content-id computes without a doc");
+    let id = id_out.trim().to_string();
+    let store_dir = dir.join("runs").join("blueprints");
+    std::fs::create_dir_all(&store_dir).expect("create store dir");
+    std::fs::write(store_dir.join(format!("{id}.json")), &envelope).expect("raw store write");
+
+    let consumer = format!(
+        r#"[
+            {{"op":"source","role":"price","kind":"F64"}},
+            {{"op":"use","ref":{{"content_id":"{id}"}},"name":"gate"}},
+            {{"op":"feed","role":"price","into":["gate.x"]}},
+            {{"op":"expose","from":"gate.out","as":"bias"}}
+        ]"#
+    );
+    let (stderr, code) = run_code_in(&dir, &["graph", "build"], &consumer);
+    assert_eq!(code, Some(1), "a doc-less fetched composite refuses -> exit 1: {stderr}");
+    assert!(stderr.contains("op 1 (use \"gate\")"), "names the op by index and instance: {stderr}");
+    assert!(stderr.contains(&id[..12]), "names the ref's id-prefix: {stderr}");
+    assert!(stderr.contains("fails the description gate"), "names the rule: {stderr}");
+    assert!(
+        stderr.contains("has no description") && stderr.contains("re-register it with a \"doc\" op"),
+        "carries the re-register hint: {stderr}"
+    );
+    assert!(stderr.contains("C29"), "cites the contract: {stderr}");
+}
+
+/// The worked acceptance flow's last leg (spec §Concrete code shapes): a
+/// pattern registered with an open param splices under an instance, and
+/// `aura sweep --list-axes` on the CONSUMER shows the path-qualified bare
+/// (unbound) axis `graph.<instance>.<node>.<param>:<kind>` — the existing
+/// nested-composite param-prefix discipline, reached through `use` this
+/// time, not a Rust-authored nested composite.
+#[test]
+fn graph_build_use_end_to_end_axes() {
+    let dir = temp_cwd("use-end-to-end-axes");
+    let bp = build_envelope_in(&dir, OPEN_PATTERN_DOC, "pattern");
+    let (reg_out, reg_err, reg_code) =
+        run_in(&dir, &["graph", "register", bp.to_str().unwrap(), "--name", "smooth"]);
+    assert_eq!(reg_code, Some(0), "register --name: {reg_out} {reg_err}");
+
+    let consumer = r#"[
+        {"op":"source","role":"price","kind":"F64"},
+        {"op":"use","ref":{"name":"smooth"},"name":"trend"},
+        {"op":"feed","role":"price","into":["trend.x"]},
+        {"op":"expose","from":"trend.out","as":"bias"}
+    ]"#;
+    let consumer_path = dir.join("consumer.ops.json");
+    std::fs::write(&consumer_path, consumer).expect("write consumer fixture");
+    let build = std::process::Command::new(BIN)
+        .args(["graph", "build"])
+        .current_dir(&dir)
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .spawn()
+        .and_then(|mut child| {
+            use std::io::Write;
+            child.stdin.take().unwrap().write_all(consumer.as_bytes())?;
+            child.wait_with_output()
+        })
+        .expect("run aura graph build");
+    assert!(build.status.success(), "consumer builds: {}", String::from_utf8_lossy(&build.stderr));
+    let consumer_bp = dir.join("consumer.bp.json");
+    std::fs::write(&consumer_bp, &build.stdout).expect("write consumer envelope");
+
+    let (axes_out, axes_err, axes_code) =
+        run_in(&dir, &["sweep", consumer_bp.to_str().unwrap(), "--list-axes"]);
+    assert_eq!(axes_code, Some(0), "list-axes: {axes_out} {axes_err}");
+    assert_eq!(
+        axes_out, "graph.trend.sma.length:I64\n",
+        "the spliced instance's open param surfaces path-qualified, bare (unbound) form"
+    );
+}
+
+/// Open patterns (#317 §"Open patterns", acceptance criterion 6): an
+/// `input`-role op-script — no bound root role at all — builds cleanly:
+/// `finish()` no longer gates root-role boundness, only `compile`/bootstrap
+/// do. The agree flow's first half (register is exercised by the other
+/// `use`-seam tests above; this pins the build step alone).
+#[test]
+fn graph_build_accepts_an_open_input_pattern() {
+    let (stdout, stderr, ok) = run(&["graph", "build"], OPEN_PATTERN_DOC);
+    assert!(ok, "an input-role pattern builds: {stderr}");
+    assert!(stdout.contains("\"input_roles\""), "carries the open root role: {stdout}");
+    assert!(!stdout.contains("\"source\""), "the role carries no bound kind (open, #317): {stdout}");
+}
+
+/// Open patterns, the OTHER half: running an open blueprint standalone
+/// still refuses — the runnability gate moved nowhere, only `finish()`
+/// stopped pre-empting it (#317). `aura run`'s `bias`-output arm re-roots
+/// through `wrap_r` (an existing, unrelated nesting mechanism unaffected by
+/// this cycle), so a bare-tap (no-`bias`) pattern is used here: its
+/// `run_measurement` path compiles the signal directly, hitting
+/// `CompileError::UnboundRootRole` at bootstrap — via the EXISTING `{e:?}`
+/// Debug rendering (a raw index, not a role name); a name mapping there is
+/// left for a follow-up (out of this cycle's scope, per the plan's own
+/// escape hatch), so this pins the existing form.
+#[test]
+fn running_an_open_blueprint_refuses_at_bootstrap() {
+    let doc = r#"[
+        {"op":"input","role":"price"},
+        {"op":"add","type":"SMA","name":"fast","bind":{"length":{"I64":2}}},
+        {"op":"feed","role":"price","into":["fast.series"]},
+        {"op":"tap","from":"fast.value","as":"fast_ma"}
+    ]"#;
+    let dir = temp_cwd("open-pattern-run-refuses");
+    let (build_out, _e, built) = run(&["graph", "build"], doc);
+    assert!(built, "an open (Input) root role finishes without root-role boundness (#317)");
+    let bp = dir.join("open.bp.json");
+    std::fs::write(&bp, &build_out).expect("write built blueprint");
+    let (stdout, stderr, code) = run_in(&dir, &["run", bp.to_str().unwrap()]);
+    assert_eq!(code, Some(1), "an open blueprint refuses standalone at bootstrap, not finish: {stdout} {stderr}");
+    assert!(stdout.is_empty(), "no report emitted on a bootstrap refusal: {stdout}");
+    assert!(
+        stderr.contains("UnboundRootRole"),
+        "the runnability gate (compile), unchanged, names the fault: {stderr}"
+    );
+}

crates/aura-cli/tests/help_self_description.rs

@@ -58,6 +58,7 @@ fn sugar_verbs_name_their_document_shape() {
 
 /// #323: `graph build --help` carries the op-list reference — the op kinds
 /// and fields are learnable from the binary, not only from serde refusals.
+/// #317: the `use` op joins the roster (nine -> ten).
 #[test]
 fn graph_build_help_carries_the_op_reference() {
     let (out, err, ok) = run(&["graph", "build", "--help"]);
@@ -72,12 +73,83 @@ fn graph_build_help_carries_the_op_reference() {
         r#"{"op":"tap""#,
         r#"{"op":"gang""#,
         r#"{"op":"doc""#,
+        r#"{"op":"use""#,
     ] {
         assert!(out.contains(op), "op reference carries {op}: {out}");
     }
     assert!(out.contains("graph introspect --vocabulary"), "points at the node roster: {out}");
 }
 
+/// #317: `graph introspect --registered` lists every registry label — row
+/// shape `<label>  <id prefix>  <root doc>` — and the empty-store form reads
+/// as prose, not a blank/garbled listing.
+#[test]
+fn graph_introspect_registered_lists_labels() {
+    let dir = std::path::Path::new(env!("CARGO_TARGET_TMPDIR")).join("aura-help-registered");
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).expect("create temp cwd");
+
+    // Empty store: prose, not a blank listing, exit 0.
+    let out_empty = Command::new(BIN)
+        .args(["graph", "introspect", "--registered"])
+        .current_dir(&dir)
+        .output()
+        .expect("spawn aura");
+    assert!(out_empty.status.success(), "empty store still exits 0");
+    assert_eq!(
+        String::from_utf8_lossy(&out_empty.stdout),
+        "no labels registered\n",
+        "the empty-store form reads as prose"
+    );
+
+    // Register + label a described open pattern, then list it.
+    let pattern = r#"[
+        {"op":"doc","text":"a reusable smoothing pattern"},
+        {"op":"input","role":"x"},
+        {"op":"add","type":"SMA","name":"sma"},
+        {"op":"feed","role":"x","into":["sma.series"]},
+        {"op":"expose","from":"sma.value","as":"out"}
+    ]"#;
+    let bp_path = dir.join("pattern.ops.json");
+    std::fs::write(&bp_path, pattern).expect("write pattern fixture");
+    let built = Command::new(BIN)
+        .args(["graph", "build"])
+        .current_dir(&dir)
+        .stdin(std::process::Stdio::piped())
+        .stdout(std::process::Stdio::piped())
+        .spawn()
+        .and_then(|mut child| {
+            use std::io::Write;
+            child.stdin.take().unwrap().write_all(pattern.as_bytes())?;
+            child.wait_with_output()
+        })
+        .expect("build the pattern");
+    assert!(built.status.success(), "the pattern builds");
+    let envelope = dir.join("pattern.bp.json");
+    std::fs::write(&envelope, &built.stdout).expect("write built envelope");
+
+    let reg = Command::new(BIN)
+        .args(["graph", "register", envelope.to_str().unwrap(), "--name", "smooth"])
+        .current_dir(&dir)
+        .output()
+        .expect("spawn aura register");
+    assert!(reg.status.success(), "register --name succeeds: {}", String::from_utf8_lossy(&reg.stderr));
+
+    let out = Command::new(BIN)
+        .args(["graph", "introspect", "--registered"])
+        .current_dir(&dir)
+        .output()
+        .expect("spawn aura");
+    assert!(out.status.success(), "listing succeeds");
+    let stdout = String::from_utf8_lossy(&out.stdout);
+    assert!(stdout.contains("smooth"), "lists the label: {stdout}");
+    assert!(stdout.contains("a reusable smoothing pattern"), "lists the root doc: {stdout}");
+    let row = stdout.lines().find(|l| l.starts_with("smooth")).expect("smooth row");
+    let fields: Vec<&str> = row.split_whitespace().collect();
+    assert_eq!(fields[1].len(), 12, "the id prefix is 12 hex chars: {row}");
+    assert!(fields[1].chars().all(|c| c.is_ascii_hexdigit()), "the prefix is hex: {row}");
+}
+
 /// #315: the node vocabulary listing carries each type's one-line meaning —
 /// no more bare names that teach nothing.
 #[test]

crates/aura-core/src/node.rs

@@ -324,7 +324,10 @@ impl PrimitiveBuilder {
 /// A fallible-bind fault — the `Result` twin of `bind`'s panics, for the
 /// data-level construction surface (`GraphSession`, #157). `bind` keeps its
 /// panic contract (and its pinned messages); `try_bind` reports the same three
-/// conditions as values.
+/// conditions as values. `AlreadyGanged` is a fourth condition `try_bind`
+/// itself never raises — only `Composite::bind_path`'s gang guard (#317
+/// follow-up) does, refusing a ganged member's raw path at the use seam
+/// before it silently de-fuses the gang.
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum BindOpError {
     /// No still-open param has this name.
@@ -333,6 +336,12 @@ pub enum BindOpError {
     AmbiguousParam(String),
     /// The value's kind does not equal the param's declared kind.
     KindMismatch { param: String, expected: ScalarKind, got: ScalarKind },
+    /// `param` (the full qualified path) is a member of the gang named
+    /// `gang` — binding it directly would freeze that one member while the
+    /// gang's public knob keeps driving its siblings. Bind the gang's own
+    /// public knob instead (accepted residue: unbindable at the use seam,
+    /// #317).
+    AlreadyGanged { param: String, gang: String },
 }
 
 /// A node's declared interface: its inputs (in order) and its output record — an

crates/aura-engine/src/blueprint.rs

@@ -15,7 +15,8 @@
 //! C23) and no external dependency (C16).
 
 use aura_core::{
-    Cell, FieldSpec, Firing, Node, NodeSchema, ParamSpec, PortSpec, PrimitiveBuilder, Scalar, ScalarKind,
+    BindOpError, Cell, FieldSpec, Firing, Node, NodeSchema, ParamSpec, PortSpec, PrimitiveBuilder, Scalar,
+    ScalarKind,
 };
 
 use crate::harness::{BootstrapError, Edge, FlatGraph, FlatTap, Harness, SourceSpec, Target};
@@ -240,6 +241,37 @@ impl Composite {
     pub fn doc(&self) -> Option<&str> {
         self.doc.as_deref()
     }
+    /// Rename this composite's render symbol in place (#317, `Op::Use`): the
+    /// interior — nodes, edges, roles, output — is untouched; only `name()`
+    /// changes, so a fetched, registered subgraph renders (and path-prefixes
+    /// its `param_space()`, via `collect_params`'s composite arm) under the
+    /// caller-chosen instance identifier instead of its own authored name.
+    pub(crate) fn renamed(mut self, name: impl Into<String>) -> Composite {
+        self.name = name.into();
+        self
+    }
+    /// Apply one path-qualified bind after `Op::Use`'s splice (#317): the
+    /// same underlying mechanic every bind goes through
+    /// (`PrimitiveBuilder::try_bind`), reached by walking `path` down through
+    /// nested composite frames by node/composite-name prefix — the segmentation
+    /// `reopen_in` (#246) also walks, but binding an open param instead of
+    /// unbinding a bound one. A path matching no node at any level is
+    /// `BindOpError::UnknownParam(path)` (the WHOLE qualified path — no open
+    /// param lives there); a path that reaches a primitive but whose leaf
+    /// param name itself is unknown/ambiguous/ill-kinded rewrites `try_bind`'s
+    /// own fault to carry the full qualified path in place of the bare leaf
+    /// name, so every fault out of this walk names the same thing: the path
+    /// the caller wrote. A path landing on a GANGED member's own param is
+    /// `BindOpError::AlreadyGanged` (review finding, #317 follow-up) — binding
+    /// it directly would silently de-fuse the gang (the member frozen while
+    /// the gang's public knob keeps driving its siblings); the gang's own
+    /// public knob stays unbindable at the use seam (accepted residue). On
+    /// `Err` `self` is dropped (consumed) — the same discard-on-ambiguity
+    /// posture `reopen` uses.
+    pub(crate) fn bind_path(mut self, path: &str, value: Scalar) -> Result<Composite, BindOpError> {
+        bind_path_in(&mut self.nodes, &self.gangs, path, path, value)?;
+        Ok(self)
+    }
     /// Install declared measurement taps (the output-side twin of `input_roles`).
     /// Fluent, mirroring `with_doc`. Empty by default.
     pub fn with_taps(mut self, taps: Vec<Tap>) -> Self {
@@ -1097,6 +1129,92 @@ fn reopen_in(items: &mut [BlueprintNode], path: &str) -> usize {
     hits
 }
 
+/// Recursive mutable walk for `Composite::bind_path` (#317): mirrors
+/// `reopen_in`'s node/composite-name prefix segmentation, but BINDS an open
+/// param (`PrimitiveBuilder::try_bind`) instead of unbinding a bound one.
+/// `full_path` is the whole original path (named in every fault this
+/// produces); `rest` is the remaining suffix at this recursion depth. `gangs`
+/// is the CURRENT frame's gang table (mirrors `collect_params`'s `gangs`
+/// parameter) — before a matched primitive's leaf param reaches `try_bind`,
+/// its (node, original-pos) is checked against every gang member; a hit
+/// refuses with `BindOpError::AlreadyGanged` rather than silently freezing
+/// the member out from under its gang's public knob (review finding,
+/// #317 follow-up). Uses `Vec::remove`/`insert` (not `&mut` in place) because
+/// `try_bind` consumes its receiver — the same reason `lower_items` moves
+/// `BlueprintNode`s by value rather than mutating through a reference.
+fn bind_path_in(
+    items: &mut Vec<BlueprintNode>,
+    gangs: &[Gang],
+    full_path: &str,
+    rest: &str,
+    value: Scalar,
+) -> Result<(), BindOpError> {
+    // The prefix this frame has already consumed off `full_path` (composite
+    // names and up) — used to qualify a gang's public name the same way
+    // `collect_params` does, so the refusal below names the SAME address
+    // `param_space()` would show for that gang.
+    let prefix = &full_path[..full_path.len() - rest.len()];
+    for i in 0..items.len() {
+        let child_rest = match &items[i] {
+            BlueprintNode::Primitive(b) => rest.strip_prefix(&format!("{}.", b.node_name())),
+            BlueprintNode::Composite(c) => rest.strip_prefix(&format!("{}.", c.name())),
+        };
+        let Some(child_rest) = child_rest else { continue };
+        let child_rest = child_rest.to_string();
+        // Gang guard (#317 follow-up review finding): a raw path landing on a
+        // GANGED member's own param must not silently freeze it while the
+        // gang's public knob keeps driving its siblings — refuse by
+        // identifier before ever reaching `try_bind`. The gang's own public
+        // knob staying unbindable at the use seam is accepted residue.
+        if let BlueprintNode::Primitive(b) = &items[i]
+            && let Some(pos) = b.params().iter().position(|p| p.name == child_rest).map(|idx| b.original_pos(idx))
+            && let Some(g) = gangs.iter().find(|g| g.members.iter().any(|m| m.node == i && m.pos == pos))
+        {
+            return Err(BindOpError::AlreadyGanged {
+                param: full_path.to_string(),
+                gang: format!("{prefix}{}", g.name),
+            });
+        }
+        let item = items.remove(i);
+        return match item {
+            BlueprintNode::Primitive(b) => match b.try_bind(&child_rest, value) {
+                Ok(b2) => {
+                    items.insert(i, BlueprintNode::Primitive(b2));
+                    Ok(())
+                }
+                Err(e) => Err(qualify_bind_error(e, full_path)),
+            },
+            BlueprintNode::Composite(mut c) => {
+                let r = bind_path_in(&mut c.nodes, &c.gangs, full_path, &child_rest, value);
+                items.insert(i, BlueprintNode::Composite(c));
+                r
+            }
+        };
+    }
+    // no node at any level matched `rest`'s leading segment: no open param
+    // lives at this path.
+    Err(BindOpError::UnknownParam(full_path.to_string()))
+}
+
+/// Rewrite a leaf `try_bind` fault to carry the FULL qualified path (#317)
+/// in place of the bare leaf param name `try_bind` only ever sees (it has no
+/// visibility past the one primitive it was called on).
+fn qualify_bind_error(e: BindOpError, full_path: &str) -> BindOpError {
+    match e {
+        BindOpError::UnknownParam(_) => BindOpError::UnknownParam(full_path.to_string()),
+        BindOpError::AmbiguousParam(_) => BindOpError::AmbiguousParam(full_path.to_string()),
+        BindOpError::KindMismatch { expected, got, .. } => {
+            BindOpError::KindMismatch { param: full_path.to_string(), expected, got }
+        }
+        // `try_bind` never raises this one (it has no gang awareness) — the
+        // gang guard above constructs it directly, already fully qualified.
+        // Kept here only so this match stays total over `BindOpError`.
+        BindOpError::AlreadyGanged { gang, .. } => {
+            BindOpError::AlreadyGanged { param: full_path.to_string(), gang }
+        }
+    }
+}
+
 /// Read-only twin of `collect_params` over the BOUND surface (#246): same
 /// recursion shape and prefix rules, but enumerating `bound_params()` (with
 /// values) instead of the open `params()`. Gangs are irrelevant here — a gang

crates/aura-engine/src/construction.rs

@@ -2,9 +2,12 @@
 //! (#157). A `GraphSession` applies `Op`s one at a time, running the
 //! eagerly-decidable checks (name resolution, edge kind-match, the >1-cover
 //! double-wire arm, param bind) at the offending op; the only-at-end-decidable
-//! checks (0-cover totality, param-namespace injectivity, root-role boundness)
+//! checks (0-cover totality, param-namespace injectivity) run holistically in
-//! run holistically in `finish`. Both cadences call the SAME §A predicates — no
+//! `finish`. Both cadences call the SAME §A predicates — no second validator
-//! second validator (C24). The node vocabulary is an injected closed resolver
+//! (C24). Root-role boundness is a *runnability* gate, not a construction gate:
+//! `finish()` does not run it (#317, open patterns), so an op-script may
+//! finish with an open root role; only `compile`/bootstrap enforce it. The
+//! node vocabulary is an injected closed resolver
 //! (`Fn(&str)->Option<PrimitiveBuilder>`), so the engine stays domain-free
 //! (invariant 9).
 
@@ -13,8 +16,8 @@ use std::collections::{HashMap, HashSet};
 use aura_core::{BindOpError, NodeSchema, PrimitiveBuilder, Scalar, ScalarKind};
 
 use crate::blueprint::{
-    check_param_namespace_injective, check_root_roles_bound, edge_kind_check, validate_wiring,
+    check_param_namespace_injective, edge_kind_check, validate_wiring, BlueprintNode, Composite,
-    BlueprintNode, Composite, Gang, GangMember, OutField, Role, Tap, TapWire,
+    Gang, GangMember, OutField, Role, Tap, TapWire,
 };
 use crate::builder::{resolve_input_slot, resolve_output_field, PortResolveError};
 use crate::harness::{Edge, Target};
@@ -46,6 +49,15 @@ pub enum Op {
     /// twin of the builder's `.doc(...)`. At most one per script; a second
     /// is a fault (a declarative script carries no last-wins ambiguity).
     Doc { text: String },
+    /// Splice a registered blueprint into the building graph as a nested
+    /// composite under an instance identifier (#317). `ref_id` is the full
+    /// content id the injected `subgraph` resolver is keyed by — the engine
+    /// never sees a label, a content-id prefix, or the registry (CLI-side
+    /// resolution happens at DTO conversion, before replay). `name` is the
+    /// instance identifier (`None` -> the fetched composite's own `name()`);
+    /// `bind` is applied path-qualified (e.g. `"sma.length"`), after the
+    /// splice.
+    Use { ref_id: String, name: Option<String>, bind: Vec<(String, Scalar)> },
 }
 
 /// A per-op construction fault, by-identifier so the cause names the op.
@@ -85,8 +97,6 @@ pub enum OpError {
     /// Holistic role-kind fault, by-identifier: a root input role fans into slots
     /// of differing scalar kinds.
     RoleKindMismatch { role: String },
-    /// Holistic root fault, by-identifier: a root input role has no bound source.
-    UnboundRootRole { role: String },
     /// Gang members must share one scalar kind.
     GangKindMismatch { member: String, expected: ScalarKind, got: ScalarKind },
     /// The param is already claimed by an earlier gang.
@@ -98,6 +108,11 @@ pub enum OpError {
     Incomplete(CompileError),
     /// A second `doc` op — the meaning line is declared at most once.
     DuplicateDoc,
+    /// `Op::Use`'s injected `subgraph` resolver found no composite for
+    /// `ref_id` (#317) — by-identifier. Unreachable from the CLI (which
+    /// resolves and fetches before replay, refusing there on a miss), but
+    /// total: a bare `replay`/`GraphSession` caller can still hit it.
+    UnknownSubgraph { ref_id: String },
 }
 
 /// A per-op-fallible blueprint accumulator. Holds the same interior data a
@@ -106,6 +121,13 @@ pub enum OpError {
 pub struct GraphSession<'v> {
     name: String,
     vocab: &'v dyn Fn(&str) -> Option<PrimitiveBuilder>,
+    /// Second injected resolver (#317), mirroring `vocab`'s closed-lookup
+    /// posture: `Op::Use` fetches a registered blueprint by full content id.
+    /// The engine stays store-free — CLI-side resolution (label/prefix,
+    /// C29 doc gate, the store fetch itself) happens at DTO conversion,
+    /// before replay; this closure is a pure lookup into an already-fetched
+    /// id->`Composite` cache. Build-free introspection paths pass `&|_| None`.
+    subgraph: &'v dyn Fn(&str) -> Option<Composite>,
     nodes: Vec<BlueprintNode>,
     schemas: Vec<NodeSchema>,
     ids: Vec<String>,
@@ -124,11 +146,17 @@ pub struct GraphSession<'v> {
 
 impl<'v> GraphSession<'v> {
     /// Start a session for a composite named `name`, resolving node types through
-    /// the injected closed vocabulary `vocab`.
+    /// the injected closed vocabulary `vocab` and registered-blueprint splices
-    pub fn new(name: impl Into<String>, vocab: &'v dyn Fn(&str) -> Option<PrimitiveBuilder>) -> Self {
+    /// (`Op::Use`, #317) through the injected `subgraph` lookup.
+    pub fn new(
+        name: impl Into<String>,
+        vocab: &'v dyn Fn(&str) -> Option<PrimitiveBuilder>,
+        subgraph: &'v dyn Fn(&str) -> Option<Composite>,
+    ) -> Self {
         Self {
             name: name.into(),
             vocab,
+            subgraph,
             nodes: Vec::new(),
             schemas: Vec::new(),
             ids: Vec::new(),
@@ -165,9 +193,47 @@ impl<'v> GraphSession<'v> {
                 self.doc = Some(text);
                 Ok(())
             }
+            Op::Use { ref_id, name, bind } => self.use_subgraph(ref_id, name, bind),
         }
     }
 
+    /// `Op::Use` (#317): fetch a registered blueprint through the injected
+    /// `subgraph` resolver, rename it to the instance identifier, apply its
+    /// path-qualified `bind` entries, and push it as an ordinary
+    /// `BlueprintNode::Composite` — sharing the node-identifier namespace
+    /// with every `Add`ed primitive (so an instance and a primitive collide
+    /// the same way two primitives do). A miss on `ref_id` is a by-identifier
+    /// `UnknownSubgraph`; a `bind` path with no matching open param anywhere
+    /// in the instance reuses the existing `BadParam` bind-fault shape,
+    /// naming the instance (`node`) and the qualified within-instance path
+    /// (`err`'s carried name) — the pair spells out the full qualified path.
+    fn use_subgraph(
+        &mut self,
+        ref_id: String,
+        name: Option<String>,
+        bind: Vec<(String, Scalar)>,
+    ) -> Result<(), OpError> {
+        let composite = (self.subgraph)(&ref_id).ok_or_else(|| OpError::UnknownSubgraph { ref_id: ref_id.clone() })?;
+        let id = name.unwrap_or_else(|| composite.name().to_string());
+        if self.names.contains_key(&id) {
+            return Err(OpError::DuplicateIdentifier(id));
+        }
+        let mut composite = composite.renamed(&id);
+        for (path, value) in bind {
+            composite = composite
+                .bind_path(&path, value)
+                .map_err(|err| OpError::BadParam { node: id.clone(), err })?;
+        }
+        let node = BlueprintNode::Composite(composite);
+        let schema = node.signature();
+        let idx = self.nodes.len();
+        self.names.insert(id.clone(), idx);
+        self.ids.push(id);
+        self.nodes.push(node);
+        self.schemas.push(schema);
+        Ok(())
+    }
+
     fn add_role(&mut self, role: String, kind: Option<ScalarKind>) -> Result<(), OpError> {
         if self.role_names.contains_key(&role) {
             return Err(OpError::DuplicateRole(role));
@@ -368,7 +434,16 @@ impl<'v> GraphSession<'v> {
             let (node_name, param_name) = Self::split_port(port)?;
             let ti = self.node_index(&node_name)?;
             let BlueprintNode::Primitive(b) = &self.nodes[ti] else {
-                unreachable!("sessions only ever add primitives")
+                // #317: `Op::Use` makes a session node legitimately a
+                // Composite, not just a Primitive — reachable now, not a
+                // defect. A gang fuses a PRIMITIVE's raw (name, pos) param
+                // slot; an instance has no such flat slot (its params are
+                // nested/path-qualified), so this is the ordinary
+                // no-such-open-param refusal, not a panic.
+                return Err(OpError::BadParam {
+                    node: node_name,
+                    err: BindOpError::UnknownParam(param_name),
+                });
             };
             let hits: Vec<usize> = b
                 .params()
@@ -426,13 +501,17 @@ impl<'v> GraphSession<'v> {
         open
     }
 
-    /// Assemble the `Composite` and run the holistic gates (totality,
+    /// Assemble the `Composite` and run the holistic construction gates (totality,
-    /// param-namespace injectivity, root-role boundness) — the SAME engine
+    /// param-namespace injectivity) — the SAME engine predicates the eager path
-    /// predicates the eager path shares, now at end-of-document cadence. The
+    /// shares, now at end-of-document cadence. Root-role boundness is
-    /// index-carrying `CompileError`s the gates return are translated back to the
+    /// deliberately NOT checked here (#317, open patterns): a `finish()`ed
-    /// surface's by-identifier `OpError` variants (slot/role names via the session's
+    /// composite may still carry an open root role, declaring a reusable
-    /// retained `ids`/`schemas` and the composite's roles); a fault with no
+    /// pattern's formal parameters; only `compile`/bootstrap (the runnability
-    /// by-identifier mapping falls through to `OpError::Incomplete`.
+    /// gate) refuse an unbound root role. The index-carrying `CompileError`s the
+    /// gates return are translated back to the surface's by-identifier `OpError`
+    /// variants (slot/role names via the session's retained `ids`/`schemas` and
+    /// the composite's roles); a fault with no by-identifier mapping falls
+    /// through to `OpError::Incomplete`.
     pub fn finish(self) -> Result<Composite, OpError> {
         let roles: Vec<Role> = self
             .roles
@@ -458,25 +537,22 @@ impl<'v> GraphSession<'v> {
             },
             other => OpError::Incomplete(other),
         })?;
-        check_root_roles_bound(c.input_roles()).map_err(|e| match e {
-            CompileError::UnboundRootRole { role } => OpError::UnboundRootRole {
-                role: c.input_roles()[role].name.clone(),
-            },
-            other => OpError::Incomplete(other),
-        })?;
         Ok(c)
     }
 }
 
 /// Replay a document of ops from scratch, stopping at the first failing op and
 /// naming it by `(op_index, OpError)`; a holistic finalize fault is attributed to
-/// index `ops.len()` (the implicit finalize step).
+/// index `ops.len()` (the implicit finalize step). `subgraph` is the injected
+/// registered-blueprint lookup `Op::Use` (#317) resolves splices through — pass
+/// `&|_| None` when no store is in play.
 pub fn replay(
     name: impl Into<String>,
     ops: Vec<Op>,
     vocab: &dyn Fn(&str) -> Option<PrimitiveBuilder>,
+    subgraph: &dyn Fn(&str) -> Option<Composite>,
 ) -> Result<Composite, (usize, OpError)> {
-    let mut s = GraphSession::new(name, vocab);
+    let mut s = GraphSession::new(name, vocab, subgraph);
     let n = ops.len();
     for (i, op) in ops.into_iter().enumerate() {
         s.apply(op).map_err(|e| (i, e))?;
@@ -487,11 +563,12 @@ pub fn replay(
 #[cfg(test)]
 mod tests {
     use super::{GraphSession, Op, OpError};
+    use crate::blueprint::{BlueprintNode, Composite, Role};
     use aura_core::{BindOpError, Scalar, ScalarKind};
     use aura_vocabulary::std_vocabulary;
 
     fn session(name: &str) -> GraphSession<'static> {
-        GraphSession::new(name, &std_vocabulary)
+        GraphSession::new(name, &std_vocabulary, &|_: &str| None)
     }
 
     #[test]
@@ -752,7 +829,7 @@ 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_vocabulary::std_vocabulary)
+        let flat = super::replay("g", ops, &aura_vocabulary::std_vocabulary, &|_: &str| None)
             .expect("replays")
             .compile_with_params(&[Scalar::i64(2), Scalar::i64(4)])
             .expect("compiles");
@@ -774,7 +851,7 @@ mod tests {
             Op::Connect { from: "b.value".into(), to: "sub.rhs".into() },
             Op::Expose { from: "sub.value".into(), as_name: "bias".into() },
         ];
-        let c = super::replay("sig", ops, &std_vocabulary).expect("replays");
+        let c = super::replay("sig", ops, &std_vocabulary, &|_: &str| None).expect("replays");
         let names: Vec<String> = c.param_space().into_iter().map(|p| p.name).collect();
         assert_eq!(names, ["length"]);
     }
@@ -820,7 +897,7 @@ mod tests {
             Op::Feed { role: "trigger".into(), into: vec!["session.trigger".into()] },
             Op::Expose { from: "session.bars_since_open".into(), as_name: "bars".into() },
         ];
-        super::replay("session_blueprint", ops, &std_vocabulary)
+        super::replay("session_blueprint", ops, &std_vocabulary, &|_: &str| None)
             .expect("the preset resolves, wires and builds through an op-script");
     }
 
@@ -922,18 +999,26 @@ mod tests {
             "finalize names the open slot by-identifier, got {err:?}");
     }
 
-    /// A reserved `Input` root role that is fed but never source-bound finishes with
+    /// #317 (open patterns): `finish()` no longer runs the root-role gate — a
-    /// the by-identifier `UnboundRootRole` (not a raw role index).
+    /// reserved `Input` root role that is fed but never source-bound now
+    /// finishes cleanly (the composite declares an open formal parameter, the
+    /// pattern's reusable interior). The runnability gate moves entirely to
+    /// `compile`, which refuses the SAME composite with the unchanged
+    /// `CompileError::UnboundRootRole` — the split this cycle ratified: finish
+    /// = construction-complete, compile = runnable.
     #[test]
-    fn finish_reports_unbound_input_root_role_by_identifier() {
+    fn finish_accepts_an_open_input_role_and_compile_refuses_it() {
         let mut s = session("g");
         s.apply(Op::Input { role: "ext".into() }).unwrap();
         s.apply(Op::Add { type_id: "Sub".into(), as_name: Some("sub".into()), bind: vec![] }).unwrap();
         s.apply(Op::Feed { role: "ext".into(), into: vec!["sub.lhs".into(), "sub.rhs".into()] }).unwrap();
         s.apply(Op::Expose { from: "sub.value".into(), as_name: "out".into() }).unwrap();
-        let err = s.finish().err().unwrap();
+        let c = s.finish().expect("finish() no longer gates root-role boundness");
-        assert!(matches!(&err, OpError::UnboundRootRole { role } if role == "ext"),
+        assert_eq!(
-            "an unbound Input root role finishes by-identifier, got {err:?}");
+            c.compile().err(),
+            Some(crate::CompileError::UnboundRootRole { role: 0 }),
+            "compile() is the runnability gate that refuses the open root role"
+        );
     }
 
     /// A root role fed into two slots of differing scalar kinds (an `f64` `Sub.lhs`
@@ -991,7 +1076,7 @@ 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_vocabulary::std_vocabulary)
+        let (idx, _err) = super::replay("g", ops, &aura_vocabulary::std_vocabulary, &|_: &str| None)
             .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
@@ -1018,7 +1103,7 @@ mod tests {
             Op::Expose { from: "s.value".into(), as_name: "out".into() },
         ];
         assert!(
-            super::replay("g", ops, &aura_vocabulary::std_vocabulary).is_err(),
+            super::replay("g", ops, &aura_vocabulary::std_vocabulary, &|_: &str| None).is_err(),
             "a self-loop op-list must be rejected (DAG invariant 5 / C9)"
         );
     }
@@ -1032,7 +1117,7 @@ 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_vocabulary::std_vocabulary).err().unwrap();
+        let err = super::replay("g", ops, &aura_vocabulary::std_vocabulary, &|_: &str| None).err().unwrap();
         assert_eq!(err, (1, OpError::UnknownNodeType("Nope".into())));
     }
 
@@ -1066,7 +1151,7 @@ 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_vocabulary::std_vocabulary)
+        let replay_flat = super::replay("root", ops, &aura_vocabulary::std_vocabulary, &|_: &str| None)
             .expect("replay resolves")
             .compile_with_params(&params)
             .expect("replay compiles");
@@ -1113,7 +1198,7 @@ mod tests {
             Op::Connect { from: "b.value".into(), to: "sub.rhs".into() },
             Op::Expose { from: "sub.value".into(), as_name: "bias".into() },
         ];
-        let replayed = super::replay("g", ops, &std_vocabulary).expect("replays");
+        let replayed = super::replay("g", ops, &std_vocabulary, &|_: &str| None).expect("replays");
 
         // (b) the GraphBuilder twin — same adds/feeds/connects/expose + g.gang(...).
         let mut g = GraphBuilder::new("g");
@@ -1165,7 +1250,7 @@ mod tests {
             Op::Tap { from: "sub.value".into(), as_name: "spread".into() },
             Op::Expose { from: "sub.value".into(), as_name: "bias".into() },
         ];
-        let replayed = super::replay("g", ops, &std_vocabulary).expect("replays");
+        let replayed = super::replay("g", ops, &std_vocabulary, &|_: &str| None).expect("replays");
 
         // (b) the GraphBuilder twin — same adds/feeds/connects + g.tap(...) / g.expose(...).
         let mut g = GraphBuilder::new("g");
@@ -1191,4 +1276,379 @@ mod tests {
         assert_eq!(replay_flat.taps, built_flat.taps);
         assert_eq!(replay_flat.edges, built_flat.edges);
     }
+
+    // ---- Op::Use (#317) -----------------------------------------------
+
+    /// A small two-node fixture composite for the `Op::Use` tests (#317): an
+    /// open `price` input role feeds an `Sma`, whose `value` feeds a `Bias`;
+    /// `Bias.bias` re-exports as `out`. Built fresh via `GraphBuilder` on every
+    /// call — mirroring how a CLI-side registry lookup hands back a freshly
+    /// loaded `Composite` each fetch — never shared or cloned (`Composite`
+    /// holds build closures and is not `Clone`).
+    fn use_fixture() -> Composite {
+        use crate::GraphBuilder;
+        use aura_std::Sma;
+        use aura_strategy::Bias;
+        let mut g = GraphBuilder::new("fixture");
+        let sma = g.add(Sma::builder().named("sma"));
+        let bias = g.add(Bias::builder().named("bias"));
+        let price = g.input_role("price");
+        g.feed(price, [sma.input("series")]);
+        g.connect(sma.output("value"), bias.input("signal"));
+        g.expose(bias.output("bias"), "out");
+        g.build().expect("fixture resolves")
+    }
+
+    /// Wrap a sink-free signal (one open input role, one exposed field) in a
+    /// runnable root that records the exposed field via a channel-backed
+    /// `Recorder`, feeds a fixed synthetic price stream through it, and
+    /// returns the recorded trace. Mirrors `blueprint_serde.rs`'s
+    /// `run_recording` test helper (same shape); duplicated here rather than
+    /// shared, since that one is private to its own file.
+    fn run_recording(signal: Composite) -> Vec<(aura_core::Timestamp, Vec<Scalar>)> {
+        use crate::harness::{Edge, Target};
+        use aura_core::Firing;
+        use aura_std::Recorder;
+        use std::sync::mpsc;
+        let (tx, rx) = mpsc::channel();
+        let root = Composite::new(
+            "h",
+            vec![
+                BlueprintNode::Composite(signal),
+                Recorder::builder(vec![ScalarKind::F64], Firing::Any, tx).into(),
+            ],
+            vec![Edge { from: 0, to: 1, slot: 0, from_field: 0 }],
+            vec![Role {
+                name: "src".into(),
+                targets: vec![Target { node: 0, slot: 0 }],
+                source: Some(ScalarKind::F64),
+            }],
+            vec![],
+        );
+        // only `bias.scale` is open (every fixture in this module's tests binds
+        // `sma.length` at the use seam), so one F64 param point.
+        let mut h = root.bootstrap_with_params(vec![Scalar::f64(0.5)]).expect("bootstraps");
+        h.run(vec![Box::new(crate::VecSource::new(crate::test_fixtures::synthetic_prices()))]);
+        rx.try_iter().collect()
+    }
+
+    /// C1 twin (#317 headline): an op-script using `Op::Use` splices a
+    /// registered-style subgraph into the building graph byte-identically to
+    /// the same splice authored directly on `GraphBuilder`
+    /// (`g.add(BlueprintNode::Composite(x))` plus the same rename/bind) — the
+    /// correctness oracle for the whole splice path. Mirrors
+    /// `replay_built_signal_compiles_identically_to_graphbuilder` (topology
+    /// identity) and `blueprint_serde::serialized_blueprint_runs_bit_identical_
+    /// to_rust_built` (bit-identical run).
+    #[test]
+    fn use_op_splices_byte_identical_to_the_rust_built_twin() {
+        use crate::blueprint_serde::blueprint_to_json;
+        use crate::GraphBuilder;
+
+        let subgraph = |ref_id: &str| (ref_id == "fixture-id").then(use_fixture);
+
+        // (a) op-script: a bound `price` source feeds the spliced instance's
+        // own "price" port (`Op::Source`, not `Op::Input` — this test
+        // bootstraps and runs the result, and only compile/bootstrap gate
+        // root-role boundness now, #317; finish() itself no longer cares);
+        // the instance's "out" field re-exports as "bias".
+        let ops = vec![
+            Op::Source { role: "price".into(), kind: ScalarKind::F64 },
+            Op::Use {
+                ref_id: "fixture-id".into(),
+                name: Some("gate".into()),
+                bind: vec![("sma.length".into(), Scalar::i64(5))],
+            },
+            Op::Feed { role: "price".into(), into: vec!["gate.price".into()] },
+            Op::Expose { from: "gate.out".into(), as_name: "bias".into() },
+        ];
+        let replayed = super::replay("root", ops, &std_vocabulary, &subgraph).expect("replays");
+
+        // (b) the GraphBuilder twin — the identical splice: the SAME fixture,
+        // renamed to "gate", the SAME bind, added the way a Rust author would.
+        let mut g = GraphBuilder::new("root");
+        let price = g.source_role("price", ScalarKind::F64);
+        let spliced = use_fixture()
+            .renamed("gate")
+            .bind_path("sma.length", Scalar::i64(5))
+            .expect("binds");
+        let gate = g.add(spliced);
+        g.feed(price, [gate.input("price")]);
+        g.expose(gate.output("out"), "bias");
+        let built = g.build().expect("root resolves");
+
+        assert_eq!(
+            blueprint_to_json(&replayed).expect("replay serializes"),
+            blueprint_to_json(&built).expect("builder serializes"),
+        );
+
+        // bootstrap + run bit-identical (only bias.scale is open: sma.length
+        // was bound at the use seam).
+        let trace_replayed = run_recording(replayed);
+        let trace_built = run_recording(built);
+        assert_eq!(
+            trace_replayed, trace_built,
+            "the op-script splice diverged from the Rust-built twin at run time"
+        );
+        assert!(!trace_replayed.is_empty(), "trace must be populated (non-degenerate)");
+    }
+
+    /// A miss on the injected `subgraph` resolver is a by-identifier fault
+    /// naming the `ref_id` (#317) — reachable directly against `GraphSession`/
+    /// `replay` even though the CLI (Task 3) always pre-resolves.
+    #[test]
+    fn use_op_unknown_subgraph_is_a_by_identifier_fault() {
+        let mut s = GraphSession::new("g", &std_vocabulary, &|_: &str| None);
+        assert_eq!(
+            s.apply(Op::Use { ref_id: "ghost".into(), name: None, bind: vec![] }),
+            Err(OpError::UnknownSubgraph { ref_id: "ghost".into() })
+        );
+    }
+
+    /// An instance identifier colliding with an already-added node is the
+    /// existing `DuplicateIdentifier` refusal — instance names share the
+    /// interior node-identifier namespace with primitives (#317).
+    #[test]
+    fn use_op_duplicate_instance_identifier_rejected() {
+        let subgraph = |_: &str| Some(use_fixture());
+        let mut s = GraphSession::new("g", &std_vocabulary, &subgraph);
+        s.apply(Op::Add { type_id: "SMA".into(), as_name: Some("gate".into()), bind: vec![] }).unwrap();
+        assert_eq!(
+            s.apply(Op::Use { ref_id: "fixture".into(), name: Some("gate".into()), bind: vec![] }),
+            Err(OpError::DuplicateIdentifier("gate".into()))
+        );
+    }
+
+    /// A post-splice `bind` path with no matching open param anywhere in the
+    /// instance faults through the existing bind-fault shape (`BadParam`),
+    /// naming the instance and the qualified within-instance path (#317).
+    #[test]
+    fn use_op_bind_of_a_closed_path_faults_with_the_qualified_path() {
+        let subgraph = |_: &str| Some(use_fixture());
+        let mut s = GraphSession::new("g", &std_vocabulary, &subgraph);
+        assert_eq!(
+            s.apply(Op::Use {
+                ref_id: "fixture".into(),
+                name: Some("gate".into()),
+                bind: vec![("ghost.length".into(), Scalar::i64(2))],
+            }),
+            Err(OpError::BadParam {
+                node: "gate".into(),
+                err: BindOpError::UnknownParam("ghost.length".into()),
+            })
+        );
+    }
+
+    /// A gang-bearing fixture for the ganged-member-bind refusal test below
+    /// (review finding, #317 follow-up): two `SMA`s ganged on `length` under
+    /// one public `channel_length` knob, feeding a `Sub` whose difference
+    /// re-exports as `out`. Mirrors `gang_op_projects_the_param_space`'s
+    /// op-script shape; built fresh on every call like `use_fixture` (never
+    /// shared/cloned — `Composite` holds build closures and is not `Clone`).
+    fn use_gang_fixture() -> Composite {
+        let ops = vec![
+            Op::Input { role: "price".into() },
+            Op::Add { type_id: "SMA".into(), as_name: Some("channel_hi".into()), bind: vec![] },
+            Op::Add { type_id: "SMA".into(), as_name: Some("channel_lo".into()), bind: vec![] },
+            Op::Gang {
+                as_name: "channel_length".into(),
+                into: vec!["channel_hi.length".into(), "channel_lo.length".into()],
+            },
+            Op::Add { type_id: "Sub".into(), as_name: None, bind: vec![] },
+            Op::Feed {
+                role: "price".into(),
+                into: vec!["channel_hi.series".into(), "channel_lo.series".into()],
+            },
+            Op::Connect { from: "channel_hi.value".into(), to: "sub.lhs".into() },
+            Op::Connect { from: "channel_lo.value".into(), to: "sub.rhs".into() },
+            Op::Expose { from: "sub.value".into(), as_name: "out".into() },
+        ];
+        super::replay("gang_fixture", ops, &std_vocabulary, &|_: &str| None).expect("gang fixture replays")
+    }
+
+    /// Silent gang de-fuse guard (review finding, #317 follow-up): binding a
+    /// GANGED member's raw path through `Op::Use`'s post-splice `bind` must
+    /// not quietly freeze that one member while the gang's public knob keeps
+    /// driving its sibling — refused by identifier, naming the full
+    /// qualified path and the gang's own public name. The gang's own public
+    /// knob (`gate.channel_length`) staying unbindable at the use seam is
+    /// accepted residue, not covered here.
+    #[test]
+    fn use_op_bind_of_a_ganged_member_path_refuses_by_identifier() {
+        let subgraph = |_: &str| Some(use_gang_fixture());
+        let mut s = GraphSession::new("g", &std_vocabulary, &subgraph);
+        assert_eq!(
+            s.apply(Op::Use {
+                ref_id: "fixture".into(),
+                name: Some("gate".into()),
+                bind: vec![("channel_hi.length".into(), Scalar::i64(20))],
+            }),
+            Err(OpError::BadParam {
+                node: "gate".into(),
+                err: BindOpError::AlreadyGanged {
+                    param: "channel_hi.length".into(),
+                    gang: "channel_length".into(),
+                },
+            })
+        );
+    }
+
+    /// Documented residue pin (#317 audit): a `gang` op cannot fuse a spliced
+    /// instance's member param — a gang fuses a PRIMITIVE's raw `(name, pos)`
+    /// slot, and an instance's params are nested/path-qualified. The refusal
+    /// is the ordinary no-such-open-param shape on the instance node, so the
+    /// authoring-guide/C24 claim "the gang op refuses a composite instance's
+    /// member path" stays an observed fact, not prose.
+    #[test]
+    fn gang_of_a_spliced_instance_member_path_refuses() {
+        let subgraph = |_: &str| Some(use_fixture());
+        let mut s = GraphSession::new("g", &std_vocabulary, &subgraph);
+        s.apply(Op::Use { ref_id: "fixture".into(), name: Some("gate".into()), bind: vec![] })
+            .unwrap();
+        s.apply(Op::Add { type_id: "SMA".into(), as_name: Some("solo".into()), bind: vec![] })
+            .unwrap();
+        assert_eq!(
+            s.apply(Op::Gang {
+                as_name: "fused".into(),
+                into: vec!["gate.sma.length".into(), "solo.length".into()],
+            }),
+            Err(OpError::BadParam {
+                node: "gate".into(),
+                err: BindOpError::UnknownParam("sma.length".into()),
+            })
+        );
+    }
+
+    /// DAG invariant (domain invariant 5 / C9), through an instance: a
+    /// `connect` closing a cycle through a spliced instance is rejected
+    /// eagerly, the instance treated as one opaque node (#317) — the same
+    /// `closes_cycle` gate `replay_rejects_dataflow_cycle` pins for primitives.
+    #[test]
+    fn use_op_connect_closing_a_cycle_through_an_instance_is_rejected_eagerly() {
+        let subgraph = |_: &str| Some(use_fixture());
+        let mut s = GraphSession::new("g", &std_vocabulary, &subgraph);
+        s.apply(Op::Add { type_id: "Sub".into(), as_name: Some("s".into()), bind: vec![] }).unwrap();
+        s.apply(Op::Use { ref_id: "fixture".into(), name: Some("gate".into()), bind: vec![] }).unwrap();
+        s.apply(Op::Connect { from: "s.value".into(), to: "gate.price".into() }).unwrap();
+        assert_eq!(
+            s.apply(Op::Connect { from: "gate.out".into(), to: "s.lhs".into() }),
+            Err(OpError::WouldCycle { from: "gate.out".into(), to: "s.lhs".into() })
+        );
+    }
+
+    /// An unfed instance in-port finishes with the by-identifier
+    /// `UnconnectedPort`, naming the instance and the instance's own role name
+    /// (rendered `<instance>.<role>` by the CLI's `format_op_error`) — the
+    /// instance's open input roles ARE its in-ports (#317).
+    #[test]
+    fn use_op_unfed_instance_role_reports_the_qualified_identifier() {
+        let subgraph = |_: &str| Some(use_fixture());
+        let mut s = GraphSession::new("g", &std_vocabulary, &subgraph);
+        s.apply(Op::Use { ref_id: "fixture".into(), name: Some("gate".into()), bind: vec![] }).unwrap();
+        s.apply(Op::Expose { from: "gate.out".into(), as_name: "bias".into() }).unwrap();
+        // gate.price deliberately left unfed.
+        let err = s.finish().err().unwrap();
+        assert!(
+            matches!(&err, OpError::UnconnectedPort { node, slot } if node == "gate" && slot == "price"),
+            "an unfed instance role finishes by-identifier as <instance>.<role>, got {err:?}"
+        );
+    }
+
+    /// An instance's still-open interior params surface path-qualified under
+    /// the instance identifier (`<instance>.<node>.<param>`, #317) — the
+    /// existing `collect_params` composite-arm prefix rule, now exercised
+    /// through `Op::Use`'s rename-on-splice (extends the
+    /// `param_space_is_flat_path_qualified_and_slot_disambiguated` family).
+    #[test]
+    fn use_op_instance_params_surface_path_qualified() {
+        let subgraph = |_: &str| Some(use_fixture());
+        let mut s = GraphSession::new("g", &std_vocabulary, &subgraph);
+        // a bound root role (mirroring the headline twin test's shape;
+        // `finish()` itself no longer cares either way, #317).
+        s.apply(Op::Source { role: "price".into(), kind: ScalarKind::F64 }).unwrap();
+        s.apply(Op::Use { ref_id: "fixture".into(), name: Some("gate".into()), bind: vec![] }).unwrap();
+        s.apply(Op::Feed { role: "price".into(), into: vec!["gate.price".into()] }).unwrap();
+        s.apply(Op::Expose { from: "gate.out".into(), as_name: "bias".into() }).unwrap();
+        let c = s.finish().expect("finishes");
+        let names: Vec<String> = c.param_space().into_iter().map(|p| p.name).collect();
+        assert_eq!(names, ["gate.sma.length", "gate.bias.scale"]);
+    }
+
+    /// Open patterns end-to-end (#317, spec §"Open patterns"): a pattern
+    /// declaring its formal parameter as an `input` role `finish()`es even
+    /// though nothing ever binds it (the root-role gate no longer runs in
+    /// `finish`), survives a real serialize/deserialize round trip through
+    /// the stored JSON form (the same bytes a registry fetch would hand
+    /// back), and a source-rooted consumer script splices the RELOADED
+    /// pattern by ref id through the injected `subgraph` lookup — the outer
+    /// script compiles and runs, proving the whole author's round trip
+    /// (build open pattern -> store -> reload -> `use` -> run), not just an
+    /// in-memory splice.
+    #[test]
+    fn open_input_pattern_finishes_registers_shaped_and_splices() {
+        use crate::blueprint_serde::{blueprint_from_json, blueprint_to_json};
+
+        // (a) the reusable pattern: an open `x` input role feeds an Sma, whose
+        // value re-exports as `out`.
+        let pattern_ops = vec![
+            Op::Input { role: "x".into() },
+            Op::Add {
+                type_id: "SMA".into(),
+                as_name: Some("sma".into()),
+                bind: vec![("length".into(), Scalar::i64(3))],
+            },
+            Op::Feed { role: "x".into(), into: vec!["sma.series".into()] },
+            Op::Expose { from: "sma.value".into(), as_name: "out".into() },
+        ];
+        let pattern = super::replay("pattern", pattern_ops, &std_vocabulary, &|_: &str| None)
+            .expect("an input-role pattern finishes without root-role boundness");
+
+        // (b) round-trip through the serialized store form.
+        let json = blueprint_to_json(&pattern).expect("an open pattern serializes");
+
+        // (c) a source-rooted outer script splices the RELOADED pattern by ref
+        // id (the injected `subgraph` lookup re-parses the stored JSON on
+        // every call, mirroring a fresh registry fetch — `Composite` is not
+        // `Clone`).
+        let subgraph = |ref_id: &str| {
+            (ref_id == "pattern-id")
+                .then(|| blueprint_from_json(&json, &std_vocabulary).expect("an open pattern deserializes"))
+        };
+        let outer_ops = vec![
+            Op::Source { role: "price".into(), kind: ScalarKind::F64 },
+            Op::Use { ref_id: "pattern-id".into(), name: Some("p".into()), bind: vec![] },
+            Op::Feed { role: "price".into(), into: vec!["p.x".into()] },
+            Op::Expose { from: "p.out".into(), as_name: "bias".into() },
+        ];
+        let outer = super::replay("root", outer_ops, &std_vocabulary, &subgraph)
+            .expect("the outer script splices the reloaded open pattern");
+
+        // (d) compiles and runs — the same recording-harness shape
+        // `run_recording` uses, but with zero open params (this pattern binds
+        // `sma.length` at the pattern seam, unlike the shared fixture, so
+        // `run_recording`'s hardcoded one-F64-param point does not apply).
+        use crate::harness::{Edge, Target};
+        use aura_core::Firing;
+        use aura_std::Recorder;
+        use std::sync::mpsc;
+        let (tx, rx) = mpsc::channel();
+        let root = Composite::new(
+            "h",
+            vec![
+                BlueprintNode::Composite(outer),
+                Recorder::builder(vec![ScalarKind::F64], Firing::Any, tx).into(),
+            ],
+            vec![Edge { from: 0, to: 1, slot: 0, from_field: 0 }],
+            vec![Role {
+                name: "src".into(),
+                targets: vec![Target { node: 0, slot: 0 }],
+                source: Some(ScalarKind::F64),
+            }],
+            vec![],
+        );
+        let mut h = root.bootstrap().expect("bootstraps with no open params");
+        h.run(vec![Box::new(crate::VecSource::new(crate::test_fixtures::synthetic_prices()))]);
+        let trace: Vec<_> = rx.try_iter().collect();
+        assert!(!trace.is_empty(), "the spliced open pattern must actually produce output");
+    }
 }

crates/aura-engine/tests/construction_e2e.rs

@@ -58,7 +58,7 @@ fn signal_ops() -> Vec<Op> {
 #[test]
 fn replayed_construction_compiles_identically_to_graphbuilder() {
     // (a) op-script replay through the public construction surface.
-    let replay_flat = replay("root", signal_ops(), &std_vocabulary)
+    let replay_flat = replay("root", signal_ops(), &std_vocabulary, &|_: &str| None)
         .expect("op-script resolves")
         .compile_with_params(&params())
         .expect("replay compiles");
@@ -103,7 +103,7 @@ fn replay_attributes_eager_fault_to_its_op_index() {
     ];
     // `.err().unwrap()` (not `unwrap_err`): the Ok arm `Composite` holds build
     // closures and is not `Debug`, which `unwrap_err`'s bound would require.
-    let err = replay("g", ops, &std_vocabulary).err().unwrap();
+    let err = replay("g", ops, &std_vocabulary, &|_: &str| None).err().unwrap();
     assert_eq!(err, (2, OpError::UnknownNodeType("Nope".into())));
 }
 
@@ -128,7 +128,7 @@ fn replay_attributes_holistic_fault_to_finalize_step() {
         // sub.rhs deliberately left unwired -> only finalize can decide totality.
     ];
     let finalize_index = ops.len(); // 6 — the implicit finalize step
-    let err = replay("g", ops, &std_vocabulary).err().unwrap();
+    let err = replay("g", ops, &std_vocabulary, &|_: &str| None).err().unwrap();
     assert!(matches!(&err, (i, OpError::UnconnectedPort { .. }) if *i == finalize_index),
         "the holistic fault is still attributed to the finalize step, got {err:?}");
 }

crates/aura-registry/src/lib.rs

@@ -173,6 +173,95 @@ impl Registry {
         }
     }
 
+    /// The label sidecar path (#317) — a sibling of `blueprint_identity_index.jsonl`,
+    /// the same "fixed-name sidecar, per-directory isolation" discipline (#191).
+    fn blueprint_names_path(&self) -> PathBuf {
+        self.path.with_file_name("blueprint_names.jsonl")
+    }
+
+    /// Raw, ungated append: one label line, unconditionally, under the
+    /// registry's write mutex (#276). No shape or content-id check —
+    /// [`Registry::put_blueprint_label`] is the gated public entry; this
+    /// exists so tests can hand-append a stale line, mirroring
+    /// `append_identity_index`.
+    fn append_blueprint_label_line(&self, name: &str, content_id: &str) -> Result<(), RegistryError> {
+        let _guard = self.append_write_lock.lock().unwrap_or_else(std::sync::PoisonError::into_inner);
+        let path = self.blueprint_names_path();
+        if let Some(parent) = path.parent().filter(|p| !p.as_os_str().is_empty()) {
+            fs::create_dir_all(parent)?;
+        }
+        let line = serde_json::to_string(&BlueprintNameLine {
+            name: name.to_string(),
+            content_id: content_id.to_string(),
+        })
+        .expect("two plain strings serialize");
+        let mut file = fs::OpenOptions::new().create(true).append(true).open(&path)?;
+        writeln!(file, "{line}")?;
+        Ok(())
+    }
+
+    /// Label a stored blueprint (#317): appends `{"name":..,"content_id":..}`
+    /// to `blueprint_names.jsonl`, a sidecar beside the identity index. Gated
+    /// on a deterministic label shape (nonempty after trim, no whitespace, no
+    /// control characters — `RegistryError::BadLabel`, C29 discipline: shape
+    /// only, never content judgement) and on `content_id` resolving via
+    /// [`Registry::get_blueprint`] (`RegistryError::UnknownBlueprint`
+    /// otherwise) — both checked BEFORE the write lock is taken. Re-labelling
+    /// an existing name appends a new line (a repoint); resolution is
+    /// latest-wins (see [`Registry::resolve_blueprint_label`]).
+    pub fn put_blueprint_label(&self, name: &str, content_id: &str) -> Result<(), RegistryError> {
+        gate_label_shape(name)?;
+        if self.get_blueprint(content_id)?.is_none() {
+            return Err(RegistryError::UnknownBlueprint(content_id.to_string()));
+        }
+        self.append_blueprint_label_line(name, content_id)
+    }
+
+    /// Resolve a label to the content id of the LATEST line naming it, skipping
+    /// any line whose content id no longer resolves via `get_blueprint`
+    /// (self-repair spirit, #191) — so "latest" always means the latest VALID
+    /// entry, even when a later append points at a since-vanished id. Missing
+    /// sidecar file -> `None` (treat-as-empty, like `load_identity_index`).
+    pub fn resolve_blueprint_label(&self, name: &str) -> Option<String> {
+        self.latest_blueprint_labels().remove(name)
+    }
+
+    /// Every registered label, latest-wins-deduped and name-sorted — the
+    /// discovery surface's data source (`graph introspect --registered`).
+    /// Dangling entries (content id no longer resolves) are skipped.
+    pub fn blueprint_labels(&self) -> Vec<(String, String)> {
+        self.latest_blueprint_labels().into_iter().collect()
+    }
+
+    /// Every content id currently stored in the blueprint store — the
+    /// candidate list a `use` ref's content-id-PREFIX resolution (#302
+    /// semantics, #317) filters against, mirroring `list_process_ids`/
+    /// `list_campaign_ids`. `blueprints_dir()` and `doc_dir("blueprints")`
+    /// name the same directory, so `list_doc_ids`'s filename-stem walk
+    /// applies unchanged.
+    pub fn list_blueprint_ids(&self) -> Result<Vec<String>, RegistryError> {
+        self.list_doc_ids("blueprints")
+    }
+
+    /// Shared latest-wins-and-dangling-skipping read of `blueprint_names.jsonl`
+    /// into a name -> content_id map (`BTreeMap` gives the name-sorted order
+    /// `blueprint_labels` promises for free). A garbage line (torn write,
+    /// manual edit) is skipped, like every other JSONL sidecar read in this
+    /// module.
+    fn latest_blueprint_labels(&self) -> std::collections::BTreeMap<String, String> {
+        let Ok(text) = fs::read_to_string(self.blueprint_names_path()) else {
+            return std::collections::BTreeMap::new();
+        };
+        let mut map = std::collections::BTreeMap::new();
+        for raw in text.lines() {
+            let Ok(line) = serde_json::from_str::<BlueprintNameLine>(raw) else { continue };
+            if self.get_blueprint(&line.content_id).ok().flatten().is_some() {
+                map.insert(line.name, line.content_id);
+            }
+        }
+        map
+    }
+
     /// The content-addressed document-store dir for one document kind —
     /// a sibling of the runs store, like `blueprints/`.
     fn doc_dir(&self, kind: &str) -> PathBuf {
@@ -273,10 +362,42 @@ impl Registry {
     }
 }
 
+/// One label->content mapping, one JSON object per line in
+/// `blueprint_names.jsonl` (#317) — the `IdentityIndexLine` sidecar-line
+/// shape, mirrored for the label store.
+#[derive(serde::Serialize, serde::Deserialize)]
+struct BlueprintNameLine {
+    name: String,
+    content_id: String,
+}
+
+/// Deterministic label-shape gate for `put_blueprint_label` (#317): nonempty
+/// after trim, no whitespace, no control characters. String shape only —
+/// never content judgement (the C29 discipline `doc_gate` also follows).
+fn gate_label_shape(name: &str) -> Result<(), RegistryError> {
+    if name.trim().is_empty() {
+        return Err(RegistryError::BadLabel { name: name.to_string(), rule: "must be nonempty" });
+    }
+    if name.chars().any(char::is_whitespace) {
+        return Err(RegistryError::BadLabel { name: name.to_string(), rule: "must not contain whitespace" });
+    }
+    if name.chars().any(|c| c.is_control()) {
+        return Err(RegistryError::BadLabel {
+            name: name.to_string(),
+            rule: "must not contain control characters",
+        });
+    }
+    Ok(())
+}
+
 /// C29 walk (#316): the root and every named nested composite must carry a
 /// gate-passing doc. `doc: None` refuses exactly like `Some("")` — both are
-/// the Empty fault ("carries no doc").
+/// the Empty fault ("carries no doc"). `pub` (#317): the `use` construction
-fn gate_composite_docs(c: &CompositeData) -> Result<(), RegistryError> {
+/// seam (`aura-cli`) re-runs this SAME walk over a freshly-fetched composite
+/// before it enters a new composition (fail fast on a doc-less fetched
+/// entry) — the one walk, two call sites (register's write-path gate, use's
+/// read-path gate), never a second implementation.
+pub fn gate_composite_docs(c: &CompositeData) -> Result<(), RegistryError> {
     let fault = match c.doc.as_deref() {
         None => Some(aura_core::DocGateFault::Empty),
         Some(d) => aura_core::doc_gate(&c.name, d).err(),
@@ -938,6 +1059,14 @@ pub enum RegistryError {
     /// the store without a gate-passing doc. Registered artifacts are never
     /// retroactively invalidated — the gate guards the write path only.
     UndescribedComposite { name: String, fault: aura_core::DocGateFault },
+    /// Label sidecar (#317): a `put_blueprint_label` name failing the
+    /// deterministic label-shape gate (nonempty after trim, no whitespace, no
+    /// control characters). By-identifier, naming the violated rule.
+    BadLabel { name: String, rule: &'static str },
+    /// Label sidecar (#317): a `put_blueprint_label` content id that does not
+    /// resolve via [`Registry::get_blueprint`] — the label sidecar never
+    /// labels a blueprint the store does not have.
+    UnknownBlueprint(String),
 }
 
 impl fmt::Display for RegistryError {
@@ -978,6 +1107,12 @@ impl fmt::Display for RegistryError {
                      its name — a registered composite describes itself (C29)"
                 ),
             },
+            RegistryError::BadLabel { name, rule } => {
+                write!(f, "blueprint label {name:?}: {rule}")
+            }
+            RegistryError::UnknownBlueprint(id) => {
+                write!(f, "blueprint: no stored blueprint with content id \"{id}\"")
+            }
         }
     }
 }
@@ -1172,6 +1307,134 @@ mod tests {
         );
     }
 
+    /// A described fixture blueprint, ready for `put_blueprint`'s C29 gate —
+    /// `put_blueprint_label`'s content-id verification routes through
+    /// `get_blueprint`, so its target must first be a gate-passing entry.
+    fn described_fixture_blueprint(name: &str) -> String {
+        format!(
+            r#"{{"format_version":1,"blueprint":{{"name":"{name}","doc":"a described fixture blueprint","nodes":[]}}}}"#
+        )
+    }
+
+    /// Property (#317): a label round-trips to the blueprint it names, and
+    /// re-labelling the SAME name repoints it — resolution and the discovery
+    /// listing both answer with the latest target, never the first.
+    #[test]
+    fn blueprint_label_round_trips_latest_wins() {
+        let reg = Registry::open(temp_family_dir("label_round_trip"));
+        let a = described_fixture_blueprint("a");
+        let b = described_fixture_blueprint("b");
+        reg.put_blueprint("ha", &a).expect("put a");
+        reg.put_blueprint("hb", &b).expect("put b");
+
+        reg.put_blueprint_label("x", "ha").expect("label x -> a");
+        assert_eq!(reg.resolve_blueprint_label("x"), Some("ha".to_string()));
+
+        reg.put_blueprint_label("x", "hb").expect("re-label x -> b");
+        assert_eq!(reg.resolve_blueprint_label("x"), Some("hb".to_string()), "latest label wins");
+        assert_eq!(
+            reg.blueprint_labels(),
+            vec![("x".to_string(), "hb".to_string())],
+            "the discovery listing dedups to the latest target",
+        );
+    }
+
+    /// Property (#317): the label-shape gate is deterministic string shape
+    /// only (nonempty after trim, no whitespace, no control characters) —
+    /// each bad shape refuses with `BadLabel` naming a (non-empty) rule.
+    #[test]
+    fn blueprint_label_refuses_bad_shapes() {
+        let reg = Registry::open(temp_family_dir("label_bad_shapes"));
+        let bp = described_fixture_blueprint("s");
+        reg.put_blueprint("h1", &bp).expect("put");
+
+        for bad in ["", "  ", "a b", "a\tb"] {
+            match reg.put_blueprint_label(bad, "h1") {
+                Err(RegistryError::BadLabel { name, rule }) => {
+                    assert_eq!(name, bad);
+                    assert!(!rule.is_empty(), "BadLabel must name the violated rule for {bad:?}");
+                }
+                other => panic!("expected BadLabel for {bad:?}, got {other:?}"),
+            }
+        }
+    }
+
+    /// Property (#317): a label may only ever point at a blueprint the store
+    /// actually has — labelling an unregistered content id refuses
+    /// by-identifier, never silently writing a dangling line.
+    #[test]
+    fn blueprint_label_refuses_unknown_content_id() {
+        let reg = Registry::open(temp_family_dir("label_unknown_id"));
+        match reg.put_blueprint_label("x", "never-written") {
+            Err(RegistryError::UnknownBlueprint(id)) => assert_eq!(id, "never-written"),
+            other => panic!("expected UnknownBlueprint, got {other:?}"),
+        }
+        assert_eq!(reg.resolve_blueprint_label("x"), None, "the refused label must not have written");
+    }
+
+    /// Property (#317, #191 spirit): a dangling LATEST line (content id no
+    /// longer resolves) is skipped by resolution, which falls back to the
+    /// earlier still-valid line for the same name — latest-wins means
+    /// latest-VALID-wins.
+    #[test]
+    fn blueprint_label_resolution_skips_a_dangling_entry() {
+        let reg = Registry::open(temp_family_dir("label_dangling"));
+        let bp = described_fixture_blueprint("s");
+        reg.put_blueprint("h1", &bp).expect("put");
+        reg.put_blueprint_label("x", "h1").expect("label x -> h1");
+
+        // hand-append a dangling line after the valid one, mirroring
+        // `append_identity_index`'s stale-line test shape: the content id it
+        // names was never registered.
+        reg.append_blueprint_label_line("x", "never-written").expect("append stale line");
+
+        assert_eq!(
+            reg.resolve_blueprint_label("x"),
+            Some("h1".to_string()),
+            "the dangling latest line is skipped; the earlier valid line for \"x\" wins",
+        );
+        assert_eq!(reg.blueprint_labels(), vec![("x".to_string(), "h1".to_string())]);
+    }
+
+    /// Property (#317, #276 discipline): N threads appending labels through
+    /// one shared `&Registry` must leave `blueprint_names.jsonl` well-formed —
+    /// every successful append surviving as its own intact, resolvable line,
+    /// none torn or merged (mirrors `concurrent_appends_keep_the_family_
+    /// store_well_formed`).
+    #[test]
+    fn concurrent_label_appends_keep_the_sidecar_well_formed() {
+        let reg = Registry::open(temp_family_dir("concurrent_label"));
+        let bp = described_fixture_blueprint("s");
+        reg.put_blueprint("h1", &bp).expect("put");
+        let n_threads = 8usize;
+        let iters = 50usize;
+
+        let total_ok: usize = std::thread::scope(|scope| {
+            let handles: Vec<_> = (0..n_threads)
+                .map(|tid| {
+                    let reg = &reg;
+                    scope.spawn(move || {
+                        let mut ok = 0usize;
+                        for iter in 0..iters {
+                            let name = format!("t{tid}-l{iter}");
+                            if reg.put_blueprint_label(&name, "h1").is_ok() {
+                                ok += 1;
+                            }
+                        }
+                        ok
+                    })
+                })
+                .collect();
+            handles.into_iter().map(|h| h.join().expect("worker thread joined")).sum()
+        });
+
+        assert_eq!(
+            reg.blueprint_labels().len(),
+            total_ok,
+            "every successful label append must survive as its own intact, resolvable entry",
+        );
+    }
+
     #[test]
     fn document_stores_round_trip_by_content_id() {
         let reg = Registry::open(temp_family_dir("document_store_round_trip"));

docs/authoring-guide.md

@@ -221,14 +221,15 @@ $ aura graph build < smacross.json > blueprint.json
 Nodes are referenced by an **identifier** (given by `add`, see below); ports
 are dotted `<identifier>.<port>` on both sides of a wire.
 
-### The nine ops
+### The ten ops
 
 | op | JSON shape | does |
 |---|---|---|
 | `doc` | `{"op":"doc","text":<str>}` | declare the composite's one-line meaning (C29) — the op-script twin of the Rust builder's `.doc(...)`. Required before `aura graph register` accepts the product (the store refuses a doc-less composite); at most one per script (a second refuses: `a doc op may appear at most once`). The text is gated: empty or merely restating the composite's name refuses at register. |
 | `source` | `{"op":"source","role":<str>,"kind":<ScalarKind>}` | reserve a bound root **source** role of `kind` — a real input the harness feeds (e.g. `"price"`). |
-| `input` | `{"op":"input","role":<str>}` | reserve an open root **input** role (kind inferred from the slots it feeds) — for a fragment meant to be wired by an *enclosing* graph. A standalone document built with `aura graph build` finalizes as a closed root, so an `input` role that is never bound refuses at the end: `finalize: root input role <name> is unbound`. |
+| `input` | `{"op":"input","role":<str>}` | reserve an open root **input** role (kind inferred from the slots it feeds) — the formal parameter of an **open pattern**, a fragment meant to be wired by an *enclosing* graph. An open pattern builds and registers like any blueprint. Running it standalone is governed by the ordinary run gates: the harness binds input roles to archive columns **by name** (C26), so a pattern whose roles match the data runs as-is; what refuses, by name, is a role the harness cannot bind — or the run surface's other gates (a signal without a bias output or tap; free knobs). |
 | `add` | `{"op":"add","type":<TypeId>,"name":<str>?,"bind":{<param>:<Scalar>}?}` | instantiate a node of a type in the closed vocabulary (`aura graph introspect --vocabulary`) — see §0 below for how a type gets into that vocabulary in the first place. `name` becomes the node's identifier for later ops (default: the type's own lowercase label — two unnamed nodes of the same type then collide). `bind` sets zero or more of its params. |
+| `use` | `{"op":"use","ref":{"content_id":<id-or-prefix>}\|{"name":<label>},"name":<str>?,"bind":{<path>:<Scalar>}?}` | splice a **registered blueprint** into the graph as a nested composite under an instance identifier (`name`; default: the stored composite's own name). The ref resolves by content id (full or unique prefix) or by a register-time label; `graph build` echoes every resolution (`aura: note: use "…": … -> <id>`) so the exact id can be pinned. The instance's open input roles wire as `<instance>.<role>`, its outputs as `<instance>.<field>`; its open params surface path-qualified (`<instance>.<node>.<param>`), sweepable (ganging an instance's params is not yet supported — the `gang` op refuses a composite instance's member path). A doc-less stored source refuses at the op (C29). The emitted blueprint contains the subgraph *inline* — no reference survives into the artifact. |
 | `feed` | `{"op":"feed","role":<str>,"into":[<port>, …]}` | fan a previously-declared role into one or more interior input slots, all-or-nothing (a failing target leaves none of the batch wired). |
 | `connect` | `{"op":"connect","from":<port>,"to":<port>}` | wire one interior output field to one interior input slot. A `connect` that would close a dataflow cycle is rejected immediately — the only legal feedback path is an explicit delay/state node (domain invariant 5). |
 | `expose` | `{"op":"expose","from":<port>,"as":<str>}` | promote an interior output field to a boundary output under the alias `as` — a real *alias* (a terminal boundary name, not a referenceable identifier like `add`'s `name`). Together with `tap`, one of the two ops whose `as` key is a terminal name rather than an identifier. |
@@ -405,6 +406,13 @@ registered blueprint 597d719b7ac607158cda3e68cd497387620397a5e93087e23da512876da
 The printed content id is the address a campaign document's `strategies[].ref`
 points at (§3).
 
+`graph register <file> --name <label>` additionally records a **blueprint
+label** — a legible, re-pointable handle for the `use` op's `{"name":…}`
+ref form (re-registering under the same label repoints it; the echo names
+the previous target). `aura graph introspect --registered` lists the
+labels with their id prefix and root doc line — the discovery surface for
+what `use` can reference.
+
 ## 2. Process documents — a validation methodology (role 5)
 
 A process document is a named, versionable pipeline of **std stage blocks**

docs/design/contracts/c24-blueprint-data.md

@@ -144,17 +144,40 @@ per-op checks — name resolution, edge kind-match (`edge_kind_check`), the doub
 arm, param bind, and acyclicity (a `connect` that would close a cycle is rejected
 eagerly at the closing op, `GraphSession::closes_cycle`, #161) — and **holistic**
 finalize checks — wiring totality (`validate_wiring`), param-namespace injectivity
-(`check_param_namespace_injective`), root-role boundness (`check_root_roles_bound`).
+(`check_param_namespace_injective`). Both cadences call the **same extracted
-Both cadences call the **same extracted predicates** — no second validator. The
+predicates** — no second validator. The holistic faults read **by-identifier**
-holistic faults read **by-identifier** (#162): `finish()` translates the
+(#162): `finish()` translates the index-carrying `CompileError`s (`UnconnectedPort` /
-index-carrying `CompileError`s (`UnconnectedPort` / `RoleKindMismatch` /
+`RoleKindMismatch`) into by-identifier `OpError` variants while still *calling* the
-`UnboundRootRole`) into by-identifier `OpError` variants while still *calling* the
+unchanged holistic gates. **Root-role boundness moved off this list (#317, open
-unchanged holistic gates. Build-free introspection answers over the closed vocabulary:
+patterns):** `check_root_roles_bound` no longer runs in `finish()` — a `finish()`ed
-`graph introspect --vocabulary | --node <T> | --unwired`. The engine `Op` stays
+op-script may still carry an open (unbound) root role, declaring a reusable
-serde-free; the wire DTO (`OpDoc`) is CLI-side (`aura-cli::graph_construct`).
+pattern's formal parameter; only `compile`/bootstrap (the runnability gate, not a
-Acceptance: a graph built purely through the ops compiles identical (C1) to its
+construction gate) still call it, unchanged. Build-free introspection answers over
-Rust-built twin, an invalid op is rejected at the op naming the cause, introspection
+the closed vocabulary: `graph introspect --vocabulary | --node <T> | --unwired`. The
-answers without a build.
+engine `Op` stays serde-free; the wire DTO (`OpDoc`) is CLI-side
+(`aura-cli::graph_construct`). Acceptance: 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.
+
+**Registered-blueprint splice (#317).** The `use` op resolves a reference — a store
+content id, a unique content-id prefix (#302 semantics), or a registry **name
+label** (`graph register --name`, latest-wins, `aura-registry`'s
+`blueprint_names.jsonl` sidecar) — to a previously registered blueprint and
+splices it into the building graph as a nested `BlueprintNode::Composite` under an
+instance identifier. The **engine never resolves**: `GraphSession`/`replay` take a
+second injected closure, `subgraph: &dyn Fn(&str) -> Option<Composite>`, mirroring
+`vocab`'s closed-lookup posture exactly — this is the same enforcement-shift
+permission §"Enforcement shift" above already grants the node vocabulary, extended
+to registered-blueprint references. All store I/O — label/prefix resolution, the
+`get_blueprint` fetch, the C29 doc-gate re-walk over the fetched composite (before
+it ever reaches the session, so a doc-less fetched entry cannot enter a NEW
+composition — a **backstop**: the register verb already gates both input forms, so
+this fires only for store content written before C29 or through the raw in-crate
+path), and the resolution echo — happens CLI-side, at DTO conversion, before
+replay; build-free introspection paths pass `&|_| None`. The echo
+(`aura: note: use "<instance>": <label-or-prefix> -> <full id>`) is the existing
+`aura: note:` benign-diagnostic marker (C14) — a new instance of the existing
+class, not a new one, so the exit-code/marker taxonomy is unchanged.
 
 **Invariant-5 lockstep.** The eager acyclicity gate is a *second* home of invariant 5
 alongside the bootstrap Kahn sort (`harness.rs`, `BootstrapError::Cycle`); the two
@@ -166,12 +189,14 @@ rejected at construction.
 
 The 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:
+`<identifier>.<port>`. The ten 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).
+  from the slots it feeds) — a reusable **pattern**'s formal parameter, left open
+  until an enclosing graph wires it (#317's open patterns): `finish()` accepts an
+  op-script that never binds it, only `compile`/bootstrap require it bound.
 - `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
@@ -196,6 +221,19 @@ replayed in order; nodes are referenced **by identifier**, ports as dotted
   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).
+- `doc` — `{"op":"doc","text":<str>}` — declare the composite's one-line meaning
+  (C29, #316) — the op-script twin of the builder's `.doc(...)`; at most one per
+  script, a second is a fault (a declarative script carries no last-wins
+  ambiguity).
+- `use` — `{"op":"use","ref":{"content_id":<str>}|{"name":<str>},"name":<str>?,"bind":{<path>:<Scalar>}?}`
+  — splice a **registered** blueprint into the building graph as a nested
+  composite under an instance identifier (`name`, defaulting to the fetched
+  composite's own name); `bind` path-qualifies the spliced instance's params
+  (e.g. `"sma.length"`), applied after the splice (#317). An instance's open
+  input roles become its `<instance>.<role>` in-ports, its output boundary
+  aliases its `<instance>.<field>` out-fields — the same `Composite` arm every
+  other add/wiring path walks, not a new mechanism. See §"The construction
+  service" below for the resolution split.
 
 Value forms are the serialized representations: a `Scalar` bind value is the typed tag
 form `{"I64":2}` / `{"F64":0.5}` / `{"Bool":true}` / `{"Timestamp":<i64>}`, and `kind`

docs/design/contracts/c29-self-description.md

@@ -27,13 +27,23 @@ cannot pass its short-name alibi
    restatement.
 3. **Register seam (data plane).** The registry's public `put_blueprint`
    parses the canonical bytes and requires a gate-passing doc on the root
-   composite and on every named nested composite — the gate guards the
+   composite and on **every** nested composite (the walk recurses
-   store boundary itself, so the register verb, every register-then-run
+   unconditionally — it does not stop at an unnamed one) — the gate guards
+   the store boundary itself, so the register verb, every register-then-run
    sugar path, and any future caller are gated by construction. The
    op-script vocabulary carries the `doc` op as the builder `.doc(...)`'s
    twin ([C25](c25-role-model.md): a closed, typed metadata construct).
    Process/campaign documents take an additive-optional top-level
    `description`, gated only when present (`DocFault::BadDescription`).
+4. **Use seam (data plane, construction-time, #317).** The `use`
+   construction op re-runs the SAME `gate_composite_docs` walk over a
+   blueprint FETCHED from the store, before it ever splices into a new
+   composition — a build-time gate on already-registered content, not a
+   second write-path check. A doc-less entry (reachable only through the
+   raw in-crate write survivor class, since `put_blueprint`'s own gate keeps
+   the store clean going forward) cannot enter a NEW composition this way,
+   but stays readable and runnable on its own — no retroactive invalidation,
+   the same discipline the Forbids clause states for the register seam.
 
 **Scope at this record's writing (#321).** The gate walks five
 vocabularies — process/campaign blocks, metrics, tap slots, tap folds, and

docs/glossary.md

@@ -31,6 +31,10 @@ A strategy's primary, backtestable DAG output: one signed, bounded `f64 ∈ [-1,
 **Avoid:** —
 The param-generic, input-role-generic graph-as-data produced by running a Rust builder; it carries free numeric params and free input roles before bootstrap. Bootstrapped into a frozen instance by binding params + data + seed. Registered and inspected headless (`aura graph register`, `aura graph introspect --params` — the raw `param_space` namespace campaign axes bind against; cycle 0107/#196); a *bound* param is an overridable **default** — a sweep axis naming it re-opens it per family (#246), while `run` uses it as-is.
 
+### blueprint label
+**Avoid:** —
+A registry-level name pointing at a registered blueprint's content id (`graph register --name <label>`, #317) — a mutable, latest-wins pointer over the immutable content-addressed store, not a second identity: re-registering under an existing label *repoints* it (the earlier content id stays reachable by its own id, never invalidated). `graph introspect --registered` lists every label with its content-id prefix and root `doc` line — the discovery surface a `use (op)` reference by name resolves against.
+
 ### bootstrap
 **Avoid:** —
 The distinct, recursive construction phase that binds `(blueprint + param-set + data bindings + seed)` into a frozen instance — buffers sized, topology fixed. The explicit name for the "wiring / graph build" that C7/C12 reference — the construction/compilation sense. Disambiguation: the *statistical* moving-block bootstrap of a trade-R series (`r_bootstrap`, `RBootstrap`) is a different thing that keeps its statistics name — it appears as the deflation null, the `aura mc` R path, and since 0108 the `std::monte_carlo` stage's `stage bootstrap` annotation; context (construction vs annotation) disambiguates.
@@ -333,6 +337,10 @@ Since #283 what CONSUMES a declared tap is itself declared per run by a **tap pl
 **Avoid:** —
 The `content id` of a run's signal blueprint in its run-record role: stamped into the manifest as `topology_hash`, keying the reproduction store and anchoring `aura reproduce` — the same SHA-256 over the same canonical bytes. Distinct from the debug-name-blind `identity id`.
 
+### use (op)
+**Avoid:** —
+The construction op that splices a **registered** blueprint into the building graph as a nested `composite` under a chosen instance name (`{"op":"use","ref":{"content_id"|"name":…},"name":…,"bind":{…}}`, #317): the reference — a content id, a unique content-id prefix, or a `blueprint label` — resolves CLI-side, before the engine ever sees it; the fetched composite is C29-gated, spliced, and its resolution echoed on stderr (`aura: note:`, the existing benign marker). The emitted blueprint carries the splice inline as an ordinary nested composite — no reference or registry dependency survives into the artifact. An instance's open input roles become its `<instance>.<role>` in-ports, its output boundary fields its `<instance>.<field>` out-fields — the existing nested-composite param-prefix discipline extends unchanged (`graph.<instance>.<node>.<param>` on `sweep --list-axes`). Pairs with the `input` op: a pattern meant to be `use`d declares its formal parameters as open `input` roles, left unbound at `finish()` (#317's open-pattern amendment) — only running it standalone requires them bound.
+
 ### veto
 **Avoid:** risk-manager
 The **optional** documented pre-trade-gate seam in the execution chain (`stop-rule → [Veto] → position-management`): position / exposure / notional caps that may reject or scale a trade. A pass-through identity DCE'd away when absent (C19/C23); kept as a named seam — it is what LEAN calls "Risk Management" and nautilus the RiskEngine.

fieldtests/composites-use/TRANSCRIPT.md

@@ -0,0 +1,122 @@
+# Fieldtest transcript — cycle #317 (composites, the `use` op)
+
+Verbatim command/output capture for the `fieldtests/composites-use/` fixtures.
+Binary: `target/release/aura` built from HEAD `4a30222` (release profile).
+Project: `./lab` (scaffolded with `aura new lab`; `/runs` gitignored).
+Commands using the store were run from inside `lab/`.
+
+## Example 1 — register → --name → discover → use by name → splice
+
+```
+$ aura graph build < cu_1_pattern_spread.ops.json
+{... "input_roles":[{"name":"price","targets":[{"node":0,"slot":0},{"node":1,"slot":0}]}] ...}
+# open pattern: input role "price" carries no "source":<kind> (contrast a source role)
+
+$ aura graph introspect --params cu_1_pattern_spread.ops.json
+fast.length:I64
+slow.length:I64
+
+$ aura graph introspect --unwired < cu_1_pattern_spread.ops.json
+# (no output — the price input role feeds fast.series/slow.series, so no open interior slot)
+
+# --- inside lab/ ---
+$ aura graph register .../cu_1_pattern_spread.ops.json --name spread_xover
+registered blueprint f61659aaa8dd1933c9e42f437f06be3ae346dd61569b5e013f07285e6fda03b1 (.../runs/blueprints/f61659....json)
+label "spread_xover" -> f61659aaa8dd1933c9e42f437f06be3ae346dd61569b5e013f07285e6fda03b1
+
+$ aura graph introspect --registered
+spread_xover  f61659aaa8dd  open SMA-crossover spread pattern: fast minus slow over an injected price input role
+
+$ aura graph build < cu_1_consumer.ops.json   > payload   2> echo
+# stderr (echo): aura: note: use "xover": spread_xover -> f61659aaa8dd1933c9e42f437f06be3ae346dd61569b5e013f07285e6fda03b1
+# stdout (payload): {... "nodes":[{"composite":{"name":"xover", ... spliced inline ...}}, {"primitive":{"type":"Bias"...}}] ...}
+
+$ aura graph introspect --params cu_1_consumer.ops.json
+xover.fast.length:I64
+xover.slow.length:I64
+bias.scale:F64
+```
+
+## Example 2 — ref-form variety + refusal UX
+
+Store contains labels `ema_smoother` (1c8edf24a1eb) and `spread_xover` (f61659aaa8dd),
+plus two unlabelled spread variants `e6982f7d...` and `e8f04011...` (both start with `e`).
+
+```
+$ aura graph register .../cu_2_docless.ops.json --name docless
+aura: blueprint: composite `graph` carries no doc — a registered composite describes itself (C29); add a doc line (...) before register
+# exit 1  (register gates doc-less at register; a doc-less entry never enters the store)
+
+# by full content id  -> splices, echoes id
+$ aura graph build < cu_2_ref_full_id.ops.json
+aura: note: use "sp": e6982f7d...d55d82 -> e6982f7d...d55d82           (exit 0)
+
+# by unique prefix "e69"  -> splices, echoes resolved id
+$ aura graph build < cu_2_ref_prefix.ops.json
+aura: note: use "sp": e69 -> e6982f7d...d55d82                         (exit 0)
+
+# by ambiguous prefix "e"  -> refuses, enumerates candidates
+$ aura graph build < cu_2_ref_ambiguous.ops.json
+aura: op 2 (use "sp"): ambiguous id "e": candidates e6982f7d...d55d82, e8f04011...07fcf8   (exit 1)
+
+# by unknown prefix "deadbeef"  -> refuses
+$ aura graph build < cu_2_ref_unknown_prefix.ops.json
+aura: op 2 (use "sp"): no registered blueprint matches content id "deadbeef"              (exit 1)
+
+# by unknown label "nope"  -> refuses, enumerates labels
+$ aura graph build < cu_2_ref_unknown_label.ops.json
+aura: op 2 (use "sp"): no registered blueprint labeled "nope" — registered labels: ema_smoother, spread_xover   (exit 1)
+```
+
+## Example 3 — running an open pattern standalone
+
+Docs (authoring guide `input` row; glossary `use (op)`) say: "only running it
+standalone refuses (bootstrap's unbound-root-role gate)."
+
+```
+# (a) spread-exposing open pattern -> refuses on the run-SHAPE gate (not the role gate)
+$ aura run spread_open.bp.json
+aura: `aura run` needs either a `bias` output (a strategy) or ≥1 declared tap (a measurement); this blueprint exposes neither   (exit 1)
+
+# (b) bias-exposing open pattern, params OPEN -> refuses on the OPEN-PARAMS gate
+$ aura run open_bias.bp.json
+aura: run requires a closed blueprint (no free parameters); 3 free knob(s) — bind them or use `aura sweep --axis`               (exit 2)
+$ aura run open_bias.bp.json --params '[{"I64":2},{"I64":4},{"F64":0.5}]'
+aura: run requires a closed blueprint (no free parameters); 3 free knob(s) — ...   (exit 2)   # --params did not close the knobs
+
+# (c) bias-exposing open pattern, params BOUND, input role "price" OPEN -> RUNS CLEAN (docs say refuse)
+$ aura run open_bias_bound.bp.json          # from cu_3_open_bias_bound.ops.json
+{"manifest":{...,"params":[],"defaults":[["graph.fast.length",{"I64":2}],...]},"metrics":{"total_pips":0.3418...}}   (exit 0)
+
+# (d) same, but input role named "quote" (not a column name) -> refuses on the ROLE-COLUMN gate
+$ aura run altrole.bp.json
+aura: input role "quote" of strategy "graph" binds to no archive column — bindable columns: open, high, low, close (alias: price), spread, volume; or bind it explicitly in the campaign data.bindings block   (exit 1)
+```
+
+## Example 4 — sweep integration + gang refusal + happy-path run
+
+```
+$ aura sweep cu_1_consumer.bp.json --list-axes
+graph.xover.fast.length:I64
+graph.xover.slow.length:I64
+graph.bias.scale:F64
+
+$ aura sweep cu_1_consumer.bp.json --axis graph.xover.fast.length=2,3 \
+    --axis graph.xover.slow.length=6 --axis graph.bias.scale=0.5 --name cu4_sweep
+{"family_id":"cu4_sweep-0","report":{"manifest":{...,"params":[["graph.xover.fast.length",{"I64":2}],["graph.xover.slow.length",{"I64":6}],...]}}}
+{"family_id":"cu4_sweep-0","report":{"manifest":{...,"params":[["graph.xover.fast.length",{"I64":3}],...]}}}
+# exit 0, 2 members — spliced-instance params sweep through the nesting
+
+# gang a spliced instance's member path -> refuses (documented), but message frames it as a missing param
+$ aura graph build < cu_4_gang_instance_member.ops.json
+aura: note: use "xover": spread_xover -> f61659...
+aura: op 6 (gang): node xover has no param "fast.length"     (exit 1)
+
+# happy path: use + splice-time bind -> closed blueprint -> run
+$ aura graph build < cu_1_consumer_bound.ops.json > closed.bp.json
+$ aura graph introspect --params cu_1_consumer_bound.ops.json     # (empty = closed)
+$ aura run closed.bp.json
+{"manifest":{...,"params":[],"defaults":[["graph.xover.fast.length",{"I64":2}],...]},"metrics":{...}}   (exit 0)
+$ aura run closed.bp.json --real GER40
+{"manifest":{...}}   (exit 0)
+```

fieldtests/composites-use/cu_1_consumer.ops.json

@@ -0,0 +1,9 @@
+[
+  {"op": "doc", "text": "consumer: splice the spread pattern by name, feed price, clamp the spread into a bias"},
+  {"op": "source", "role": "price", "kind": "F64"},
+  {"op": "use", "ref": {"name": "spread_xover"}, "name": "xover"},
+  {"op": "feed", "role": "price", "into": ["xover.price"]},
+  {"op": "add", "type": "Bias", "name": "bias"},
+  {"op": "connect", "from": "xover.spread", "to": "bias.signal"},
+  {"op": "expose", "from": "bias.bias", "as": "bias"}
+]

fieldtests/composites-use/cu_1_consumer_bound.ops.json

@@ -0,0 +1,9 @@
+[
+  {"op": "doc", "text": "consumer that splices the spread pattern, binds its params at the use seam, and clamps to a bias — a closed, runnable blueprint"},
+  {"op": "source", "role": "price", "kind": "F64"},
+  {"op": "use", "ref": {"name": "spread_xover"}, "name": "xover", "bind": {"fast.length": {"I64": 2}, "slow.length": {"I64": 6}}},
+  {"op": "feed", "role": "price", "into": ["xover.price"]},
+  {"op": "add", "type": "Bias", "name": "bias", "bind": {"scale": {"F64": 0.5}}},
+  {"op": "connect", "from": "xover.spread", "to": "bias.signal"},
+  {"op": "expose", "from": "bias.bias", "as": "bias"}
+]

fieldtests/composites-use/cu_1_pattern_spread.ops.json

@@ -0,0 +1,11 @@
+[
+  {"op": "doc", "text": "open SMA-crossover spread pattern: fast minus slow over an injected price input role"},
+  {"op": "input", "role": "price"},
+  {"op": "add", "type": "SMA", "name": "fast"},
+  {"op": "add", "type": "SMA", "name": "slow"},
+  {"op": "feed", "role": "price", "into": ["fast.series", "slow.series"]},
+  {"op": "add", "type": "Sub", "name": "sub"},
+  {"op": "connect", "from": "fast.value", "to": "sub.lhs"},
+  {"op": "connect", "from": "slow.value", "to": "sub.rhs"},
+  {"op": "expose", "from": "sub.value", "as": "spread"}
+]

fieldtests/composites-use/cu_2_docless.ops.json

@@ -0,0 +1,6 @@
+[
+  {"op": "input", "role": "price"},
+  {"op": "add", "type": "EMA", "name": "e"},
+  {"op": "feed", "role": "price", "into": ["e.series"]},
+  {"op": "expose", "from": "e.value", "as": "smoothed"}
+]

fieldtests/composites-use/cu_2_ema_smoother.ops.json

@@ -0,0 +1,7 @@
+[
+  {"op": "doc", "text": "open EMA smoother pattern: exponential moving average over an injected price input role"},
+  {"op": "input", "role": "price"},
+  {"op": "add", "type": "EMA", "name": "e"},
+  {"op": "feed", "role": "price", "into": ["e.series"]},
+  {"op": "expose", "from": "e.value", "as": "smoothed"}
+]

fieldtests/composites-use/cu_2_ref_ambiguous.ops.json

@@ -0,0 +1,7 @@
+[
+  {"op": "doc", "text": "ref by an ambiguous one-char prefix (two ids start with e)"},
+  {"op": "source", "role": "price", "kind": "F64"},
+  {"op": "use", "ref": {"content_id": "e"}, "name": "sp"},
+  {"op": "feed", "role": "price", "into": ["sp.price"]},
+  {"op": "expose", "from": "sp.spread", "as": "spread"}
+]

fieldtests/composites-use/cu_2_ref_full_id.ops.json

@@ -0,0 +1,7 @@
+[
+  {"op": "doc", "text": "ref a registered spread by full content id"},
+  {"op": "source", "role": "price", "kind": "F64"},
+  {"op": "use", "ref": {"content_id": "e6982f7d4ad35dd59f1d9835e10436c193735d94501b7d10518eae0d9cd55d82"}, "name": "sp"},
+  {"op": "feed", "role": "price", "into": ["sp.price"]},
+  {"op": "expose", "from": "sp.spread", "as": "spread"}
+]

fieldtests/composites-use/cu_2_ref_prefix.ops.json

@@ -0,0 +1,7 @@
+[
+  {"op": "doc", "text": "ref a registered spread by unique content-id prefix"},
+  {"op": "source", "role": "price", "kind": "F64"},
+  {"op": "use", "ref": {"content_id": "e69"}, "name": "sp"},
+  {"op": "feed", "role": "price", "into": ["sp.price"]},
+  {"op": "expose", "from": "sp.spread", "as": "spread"}
+]

fieldtests/composites-use/cu_2_ref_unknown_label.ops.json

@@ -0,0 +1,7 @@
+[
+  {"op": "doc", "text": "ref by a label that was never registered"},
+  {"op": "source", "role": "price", "kind": "F64"},
+  {"op": "use", "ref": {"name": "nope"}, "name": "sp"},
+  {"op": "feed", "role": "price", "into": ["sp.price"]},
+  {"op": "expose", "from": "sp.spread", "as": "spread"}
+]

fieldtests/composites-use/cu_2_ref_unknown_prefix.ops.json

@@ -0,0 +1,7 @@
+[
+  {"op": "doc", "text": "ref by a prefix that matches nothing in the store"},
+  {"op": "source", "role": "price", "kind": "F64"},
+  {"op": "use", "ref": {"content_id": "deadbeef"}, "name": "sp"},
+  {"op": "feed", "role": "price", "into": ["sp.price"]},
+  {"op": "expose", "from": "sp.spread", "as": "spread"}
+]

fieldtests/composites-use/cu_2_spread_variant2.ops.json

@@ -0,0 +1,11 @@
+[
+  {"op": "doc", "text": "spread pattern variant 2 for prefix ambiguity probe"},
+  {"op": "input", "role": "price"},
+  {"op": "add", "type": "SMA", "name": "fast"},
+  {"op": "add", "type": "SMA", "name": "slow"},
+  {"op": "feed", "role": "price", "into": ["fast.series", "slow.series"]},
+  {"op": "add", "type": "Sub", "name": "sub"},
+  {"op": "connect", "from": "fast.value", "to": "sub.lhs"},
+  {"op": "connect", "from": "slow.value", "to": "sub.rhs"},
+  {"op": "expose", "from": "sub.value", "as": "spread"}
+]

fieldtests/composites-use/cu_2_spread_variant5.ops.json

@@ -0,0 +1,11 @@
+[
+  {"op": "doc", "text": "spread pattern variant 5 for prefix ambiguity probe"},
+  {"op": "input", "role": "price"},
+  {"op": "add", "type": "SMA", "name": "fast"},
+  {"op": "add", "type": "SMA", "name": "slow"},
+  {"op": "feed", "role": "price", "into": ["fast.series", "slow.series"]},
+  {"op": "add", "type": "Sub", "name": "sub"},
+  {"op": "connect", "from": "fast.value", "to": "sub.lhs"},
+  {"op": "connect", "from": "slow.value", "to": "sub.rhs"},
+  {"op": "expose", "from": "sub.value", "as": "spread"}
+]

fieldtests/composites-use/cu_3_open_bias.ops.json

@@ -0,0 +1,13 @@
+[
+  {"op": "doc", "text": "open bias pattern: SMA-crossover spread clamped to a bias, over an injected price input role"},
+  {"op": "input", "role": "price"},
+  {"op": "add", "type": "SMA", "name": "fast"},
+  {"op": "add", "type": "SMA", "name": "slow"},
+  {"op": "feed", "role": "price", "into": ["fast.series", "slow.series"]},
+  {"op": "add", "type": "Sub", "name": "sub"},
+  {"op": "connect", "from": "fast.value", "to": "sub.lhs"},
+  {"op": "connect", "from": "slow.value", "to": "sub.rhs"},
+  {"op": "add", "type": "Bias", "name": "bias"},
+  {"op": "connect", "from": "sub.value", "to": "bias.signal"},
+  {"op": "expose", "from": "bias.bias", "as": "bias"}
+]

fieldtests/composites-use/cu_3_open_bias_bound.ops.json

@@ -0,0 +1,13 @@
+[
+  {"op": "doc", "text": "open bias pattern with params bound but the price input role still open — isolates the standalone-run input-role refusal"},
+  {"op": "input", "role": "price"},
+  {"op": "add", "type": "SMA", "name": "fast", "bind": {"length": {"I64": 2}}},
+  {"op": "add", "type": "SMA", "name": "slow", "bind": {"length": {"I64": 4}}},
+  {"op": "feed", "role": "price", "into": ["fast.series", "slow.series"]},
+  {"op": "add", "type": "Sub", "name": "sub"},
+  {"op": "connect", "from": "fast.value", "to": "sub.lhs"},
+  {"op": "connect", "from": "slow.value", "to": "sub.rhs"},
+  {"op": "add", "type": "Bias", "name": "bias", "bind": {"scale": {"F64": 0.5}}},
+  {"op": "connect", "from": "sub.value", "to": "bias.signal"},
+  {"op": "expose", "from": "bias.bias", "as": "bias"}
+]

fieldtests/composites-use/cu_4_gang_instance_member.ops.json

@@ -0,0 +1,10 @@
+[
+  {"op": "doc", "text": "consumer that tries to gang two params of a spliced instance (documented as unsupported)"},
+  {"op": "source", "role": "price", "kind": "F64"},
+  {"op": "use", "ref": {"name": "spread_xover"}, "name": "xover"},
+  {"op": "feed", "role": "price", "into": ["xover.price"]},
+  {"op": "add", "type": "Bias", "name": "bias"},
+  {"op": "connect", "from": "xover.spread", "to": "bias.signal"},
+  {"op": "gang", "as": "xover_length", "into": ["xover.fast.length", "xover.slow.length"]},
+  {"op": "expose", "from": "bias.bias", "as": "bias"}
+]

fieldtests/composites-use/lab/.gitignore

@@ -0,0 +1 @@
+/runs

fieldtests/composites-use/lab/Aura.toml

@@ -0,0 +1,4 @@
+# Static project context only (C17); paths only.
+[paths]
+runs = "runs"
+# data = "/path/to/archive"  # the recorded-data root; defaults to the built-in path

fieldtests/composites-use/lab/CLAUDE.md

@@ -0,0 +1,22 @@
+# lab — an aura research project (data-only)
+
+This directory is an aura project: blueprints + research documents over the
+std vocabulary, anchored by `Aura.toml`. There is no crate and no build step.
+
+- Run:   `aura run blueprints/signal.json` (the starter is closed — all
+  params bound; bound values are defaults — any `--axis` may override them
+  (#246))
+- Sweep: `aura sweep blueprints/signal.json --axis lab_signal.fast.length=2,4,8`
+  (`aura sweep <bp> --list-axes` lists the open + bound-overridable axes)
+- Native nodes: when the project needs its first project-specific node,
+  `aura nodes new <name>` scaffolds a node crate beside this project and
+  attaches it via `[nodes]` in `Aura.toml` (build it with `cargo build`).
+- Topology is data (`blueprints/*.json`); results land in `runs/`.
+- Execution model: a strategy emits a bias in [-1,+1] per cycle, held as the
+  continuously-tracked target position; a protective stop defines the risk
+  unit R, and quality metrics are R-based. Entry signals become held state
+  via the signal-side latch/edge-pulse idiom (see
+  `aura graph introspect --vocabulary`).
+- Data plane: the research verbs are sugar over registered process/campaign
+  documents — author them directly with `aura process` / `aura campaign`,
+  growing one from a bare `{}` via `aura campaign introspect --unwired`.

fieldtests/composites-use/lab/blueprints/signal.json

@@ -0,0 +1 @@
+{"format_version":1,"blueprint":{"name":"lab_signal","doc":"fast/slow SMA difference clamped into a directional bias","nodes":[{"primitive":{"type":"SMA","name":"fast","bound":[{"pos":0,"name":"length","kind":"I64","value":{"I64":2}}]}},{"primitive":{"type":"SMA","name":"slow","bound":[{"pos":0,"name":"length","kind":"I64","value":{"I64":4}}]}},{"primitive":{"type":"Sub"}},{"primitive":{"type":"Bias","name":"bias","bound":[{"pos":0,"name":"scale","kind":"F64","value":{"F64":0.5}}]}}],"edges":[{"from":0,"to":2,"slot":0,"from_field":0},{"from":1,"to":2,"slot":1,"from_field":0},{"from":2,"to":3,"slot":0,"from_field":0}],"input_roles":[{"name":"price","targets":[{"node":0,"slot":0},{"node":1,"slot":0}],"source":"F64"}],"output":[{"node":3,"field":0,"name":"bias"}]}}