feat(aura-cli, aura-engine): graph introspect --taps — positive declared-tap discovery

Harvest sweep, batch 3 of 6 (first half).

Composite::declared_taps() walks the blueprint depth-first collecting
(tap name, source wire, column kind), names bare at every depth —
mirroring inline_composite's hoist, where a tap's name IS the flat
graph's load-bearing identifier — and bounds-total over invalid wires
(compile's validate_wiring stays the real gate). The CLI view loads
like --params (FILE gates the authored root name, a content id does
not), prints one 'name  node.field  Kind' row per tap, and renders the
tap-less case as a stderr note with empty stdout, exit 0.

Closes the recovery-only discovery loop: since #333 the only way to
learn a blueprint's declared tap names was provoking the undeclared-tap
refusal roster.

closes #337

crates/aura-cli/tests/graph_construct.rs

@@ -832,6 +832,54 @@ fn graph_params_tolerates_content_prefix_on_target() {
     );
 }
 
+/// Property (#337): `--taps <FILE>` is the positive declared-tap discovery
+/// view — before this, the only way to learn a blueprint's declared tap names
+/// was provoking #333's undeclared-tap refusal roster. One row per declared
+/// tap: name, source wire (`node.field`), column kind, in declaration order.
+#[test]
+fn graph_introspect_taps_lists_declared_taps_wire_and_kind() {
+    let dir = temp_cwd("taps-listed");
+    let ops = r#"[
+        {"op":"source","role":"price","kind":"F64"},
+        {"op":"add","type":"SMA","name":"fast","bind":{"length":{"I64":2}}},
+        {"op":"add","type":"SMA","name":"slow","bind":{"length":{"I64":4}}},
+        {"op":"add","type":"Sub"},
+        {"op":"feed","role":"price","into":["fast.series","slow.series"]},
+        {"op":"connect","from":"fast.value","to":"sub.lhs"},
+        {"op":"connect","from":"slow.value","to":"sub.rhs"},
+        {"op":"tap","from":"fast.value","as":"fast_ma"},
+        {"op":"tap","from":"sub.value","as":"spread"},
+        {"op":"expose","from":"sub.value","as":"bias"}
+    ]"#;
+    let (build_out, build_err, build_code) = run_in_stdin(&dir, &["graph", "build"], ops);
+    assert_eq!(build_code, Some(0), "graph build: {build_out} {build_err}");
+    let bp = dir.join("tapped.json");
+    std::fs::write(&bp, &build_out).expect("write built blueprint");
+    let (stdout, stderr, code) =
+        run_in(&dir, &["graph", "introspect", "--taps", bp.to_str().unwrap()]);
+    assert_eq!(code, Some(0), "stdout: {stdout} stderr: {stderr}");
+    assert_eq!(
+        stdout, "fast_ma  fast.value  F64\nspread  sub.value  F64\n",
+        "one row per declared tap: name, source wire, column kind"
+    );
+}
+
+/// Property (#337): a blueprint with no declared taps prints nothing to
+/// stdout (nothing was declared to list) plus a one-line stderr note — a
+/// listing, not a fault, exit 0.
+#[test]
+fn graph_introspect_taps_reports_no_taps_on_stderr_when_none_declared() {
+    let dir = temp_cwd("taps-empty");
+    let bp = fixture("r_sma_open.json");
+    let (stdout, stderr, code) = run_in(&dir, &["graph", "introspect", "--taps", &bp]);
+    assert_eq!(code, Some(0), "a tap-less blueprint is a listing, not a fault: {stderr}");
+    assert_eq!(stdout, "", "no declared taps to list: {stdout}");
+    assert!(
+        stderr.contains("declares no taps"),
+        "stderr carries the one-line note: {stderr}"
+    );
+}
+
 /// Property (#196, negative): `--params <ID>` with a well-shaped 64-hex id
 /// that was never registered refuses with a store-miss message, not a panic
 /// or a silent empty namespace — the registry lookup branch of