feat(cli): three-way unresolved-namespace hint (#241 T3)

A project-namespaced (::) unknown type id now hints by tier: outside
any project the existing "no Aura.toml was found" text stays
byte-identical; inside a data-only project the hint names the missing
node crate and the attach verb (aura nodes new); a loaded node crate
gets no hint (the vocabulary error carries the message).

refs #241

crates/aura-cli/src/graph_construct.rs

@@ -376,18 +376,25 @@ fn gang_fault_prose(e: &CompileError) -> String {
     }
 }
 
-/// (#185) When an unresolved type id LOOKS project-namespaced (`::`) but no
-/// project was loaded for this invocation (`env.provenance()` is `None`),
-/// append a hint pointing at the missing `Aura.toml` — the likeliest cause is
-/// "ran outside the project directory", not "genuinely unknown std id". Bare
-/// std-vocabulary ids (no `::`) and invocations that DO have a project loaded
-/// get no hint.
+/// (#185/#241) When an unresolved type id LOOKS project-namespaced (`::`),
+/// the likeliest causes are environmental, tiered: outside any project the
+/// hint points at the missing `Aura.toml`; inside a data-only project it
+/// points at the missing node crate. Bare std ids (no `::`) and invocations
+/// with a loaded node crate get no hint (the vocabulary error carries the
+/// message).
 pub(crate) fn unresolved_namespace_hint(e: &LoadError, env: &crate::project::Env) -> Option<String> {
     match e {
-        LoadError::UnknownNodeType(t) if t.contains("::") && env.provenance().is_none() => Some(
-            "type id looks project-namespaced but no Aura.toml was found — run inside a project directory"
-                .to_string(),
-        ),
+        LoadError::UnknownNodeType(t) if t.contains("::") => match env.provenance() {
+            None => Some(
+                "type id looks project-namespaced but no Aura.toml was found — run inside a project directory"
+                    .to_string(),
+            ),
+            Some(p) if p.namespace.is_none() => Some(
+                "type id looks project-namespaced but this project binds no node crate — attach one with `aura nodes new <name>`"
+                    .to_string(),
+            ),
+            Some(_) => None,
+        },
         _ => None,
     }
 }

crates/aura-cli/tests/project_load.rs

@@ -365,6 +365,27 @@ fn nodes_pointer_crate_resolves_and_stamps_its_namespace() {
     );
 }
 
+/// #241: inside a data-only project, a project-namespaced type id gets the
+/// "binds no node crate" hint (not the outside-project "no Aura.toml" text).
+#[test]
+fn data_only_project_hints_attach_for_namespaced_ids() {
+    let tmp = std::env::temp_dir().join(format!("aura-dataonly-hint-{}", std::process::id()));
+    std::fs::create_dir_all(&tmp).unwrap();
+    std::fs::write(tmp.join("Aura.toml"), "").unwrap();
+    let bp = tmp.join("bp.json");
+    std::fs::write(&bp, r#"{"format_version":1,"blueprint":{"name":"x","nodes":[{"primitive":{"type":"nosuch::Node"}}],"edges":[],"input_roles":[{"name":"price","targets":[{"node":0,"slot":0}],"source":"F64"}],"output":[{"node":0,"field":0,"name":"bias"}]}}"#).unwrap();
+    let out = std::process::Command::new(env!("CARGO_BIN_EXE_aura"))
+        .args(["run", bp.to_str().unwrap()])
+        .current_dir(&tmp)
+        .output()
+        .expect("spawn aura");
+    assert_eq!(out.status.code(), Some(2), "stderr: {}", String::from_utf8_lossy(&out.stderr));
+    let err = String::from_utf8_lossy(&out.stderr);
+    assert!(err.contains("binds no node crate"), "{err}");
+    assert!(err.contains("aura nodes new"), "{err}");
+    std::fs::remove_dir_all(&tmp).ok();
+}
+
 #[test]
 fn missing_artifact_refuses_with_build_hint() {
     // A minimal never-built project: valid cargo metadata, no dylib on disk.