feat(cli): the scaffold ships one starter blueprint

Task 6 of the bound-override cycle: SIGNAL_OPEN_JSON_STD and its write
retire — aura new scaffolds signal.json alone, and the project CLAUDE.md
quickstart advertises run AND sweep against that one file (the sweep line
overrides the bound fast.length; --list-axes shows open + bound axes).
The data-only e2e loop proves it end to end: scaffold, run the closed
starter, sweep it via an override axis, and assert signal.json is the
only starter blueprint. The authoring-guide's starter-pair sentence is
retargeted; the last signal_open reference outside the unrelated #196
fixture string is gone.

refs #246

crates/aura-cli/tests/project_new.rs

@@ -79,11 +79,15 @@ fn new_scaffolds_and_runs_the_data_only_loop() {
         "Aura.toml",
         ".gitignore",
         "blueprints/signal.json",
-        "blueprints/signal_open.json",
         "CLAUDE.md",
     ] {
         assert!(proj.join(f).is_file(), "missing scaffolded file {f}");
     }
+    assert_eq!(
+        std::fs::read_dir(proj.join("blueprints")).unwrap().count(),
+        1,
+        "blueprints/signal.json must be the ONLY starter blueprint (#246)"
+    );
     assert!(!proj.join("Cargo.toml").exists(), "data-only project must have no Cargo.toml");
     assert!(!proj.join("src/lib.rs").exists(), "data-only project must have no src/lib.rs");
 
@@ -108,15 +112,11 @@ fn new_scaffolds_and_runs_the_data_only_loop() {
 }
 
 /// #241 headline: a fresh data-only project sweeps a dissolved verb (#218's
-/// gate) with zero build step — using the scaffolded open starter blueprint
-/// and the exact axis the scaffolded CLAUDE.md advertises.
+/// gate) with zero build step — using the scaffolded (closed) starter
+/// blueprint and the exact axis the scaffolded CLAUDE.md advertises.
 ///
-/// Why a second starter blueprint exists at all: `aura run` requires a
-/// CLOSED blueprint (every param bound) while `aura sweep` requires OPEN
-/// knobs ("this blueprint is fully bound; nothing to sweep"), so one file
-/// cannot serve both quickstart lines. `blueprints/signal.json` stays closed
-/// for the run headline above; `blueprints/signal_open.json` leaves
-/// `fast.length` free for this one.
+/// #246: the closed starter IS the sweep target — a bound param is a default
+/// an axis overrides.
 #[test]
 fn data_only_project_sweeps_without_any_build() {
     let base = tmp("sweep");
@@ -124,7 +124,7 @@ fn data_only_project_sweeps_without_any_build() {
     assert!(new.status.success(), "{}", String::from_utf8_lossy(&new.stderr));
     let proj = base.join("scratch");
     let out = aura(
-        &["sweep", "blueprints/signal_open.json", "--axis", "scratch_signal_open.fast.length=2,4"],
+        &["sweep", "blueprints/signal.json", "--axis", "scratch_signal.fast.length=2,4"],
         &proj,
     );
     assert!(out.status.success(), "stderr: {}", String::from_utf8_lossy(&out.stderr));
@@ -132,6 +132,36 @@ fn data_only_project_sweeps_without_any_build() {
     let _ = std::fs::remove_dir_all(&base);
 }
 
+/// Property (#246): the scaffold's sweep quickstart genuinely re-opens the
+/// bound `fast.length` param — the persisted family has exactly one member
+/// per axis value, not a single collapsed member. A silent regression where
+/// the bound-param override is dropped (member always built from the
+/// blueprint's own default) would still exit 0 and still create a `runs`
+/// store, so `data_only_project_sweeps_without_any_build` above cannot catch
+/// it; only the member count can.
+#[test]
+fn data_only_project_sweep_over_the_starter_opens_one_member_per_axis_value() {
+    let base = tmp("sweep-members");
+    let new = aura(&["new", "scratch"], &base);
+    assert!(new.status.success(), "{}", String::from_utf8_lossy(&new.stderr));
+    let proj = base.join("scratch");
+    let out = aura(
+        &["sweep", "blueprints/signal.json", "--axis", "scratch_signal.fast.length=2,4,8"],
+        &proj,
+    );
+    assert!(out.status.success(), "stderr: {}", String::from_utf8_lossy(&out.stderr));
+    let fams = aura(&["runs", "families"], &proj);
+    assert!(fams.status.success(), "runs families exit: {:?}", fams.status);
+    let fams_out = String::from_utf8_lossy(&fams.stdout).into_owned();
+    assert_eq!(fams_out.lines().count(), 1, "exactly one family persisted: {fams_out}");
+    assert!(
+        fams_out.contains("\"members\":3"),
+        "the three-value bound-param axis grid must yield three members, one per \
+         value (2,4,8) — not a collapsed default-only sweep: {fams_out}"
+    );
+    let _ = std::fs::remove_dir_all(&base);
+}
+
 #[test]
 fn new_refuses_an_existing_destination() {
     let base = tmp("exists");
@@ -186,11 +216,15 @@ fn new_inside_a_work_tree_skips_the_nested_git() {
         "Aura.toml",
         ".gitignore",
         "blueprints/signal.json",
-        "blueprints/signal_open.json",
         "CLAUDE.md",
     ] {
         assert!(proj.join(f).is_file(), "missing scaffolded file {f}");
     }
+    assert_eq!(
+        std::fs::read_dir(proj.join("blueprints")).unwrap().count(),
+        1,
+        "blueprints/signal.json must be the ONLY starter blueprint (#246)"
+    );
     // ...but without a nested repo of its own.
     assert!(
         !proj.join(".git").exists(),