test(cli),docs: risk-axis introspection pins + guide/glossary coverage (#216 slice 2)

closes #216

The remaining introspection e2e pins: the bare-{} envelope probe (the
issue's exact reproduction) lists the optional risk slot; a bound
(non-empty) risk list closes it (no open slots); an EXPLICIT empty
'risk': [] still counts as open (pins the non-emptiness branch, which an
is_none()-based probe would get wrong); the --block std::risk assert is
sharpened to pin the optional rendering and the block doc line (the old
bare contains("risk") matched std::risk trivially).

Docs: the authoring guide's bare-{} transcript gains the risk line, the
§3 worked example gains a two-regime risk section (heading updated), a
prose paragraph explains the structural risk axis (stop defines R;
absent = the same default vol regime the verbs bind), and both validate
transcripts show the new matrix counts. The glossary gains the
'risk regime' entry (canonical term; avoid: stop regime, risk section).

Verified: cargo test --workspace 62 result groups / 0 failures; clippy
-D warnings clean; cargo doc 0 warnings; the guide's transcript strings
grep-match the shipped hint/summary bytes (1/2/1).

crates/aura-cli/tests/research_docs.rs

@@ -615,7 +615,14 @@ fn campaign_introspect_block_risk_describes_the_regime_shape() {
         out.contains("list of stop regimes { vol: { length, k } }; absent = one default regime"),
         "the block description must name the regime shape: {out}"
     );
-    assert!(out.contains("risk"), "stdout/stderr: {out}");
+    assert!(
+        out.contains("optional, list of stop regimes { vol: { length, k } }; absent = one default regime"),
+        "the risk slot must render as optional: {out}"
+    );
+    assert!(
+        out.contains("std::risk — campaign section: the structural risk axis"),
+        "stdout/stderr: {out}"
+    );
 }
 
 /// #216: a complete-but-risk-less campaign document (the exact shape a
@@ -639,6 +646,63 @@ fn campaign_introspect_unwired_lists_the_risk_slot_when_absent() {
     );
 }
 
+/// #216: the bare-envelope probe (`{}` — the issue's exact reproduction)
+/// names the optional risk axis alongside the required envelope slots.
+#[test]
+fn campaign_introspect_unwired_lists_the_optional_risk_slot_on_bare_envelope() {
+    let dir = temp_cwd("campaign-introspect-unwired-risk-bare");
+    write_doc(&dir, "bare.json", "{}");
+    let (out, code) = run_code_in(&dir, &["campaign", "introspect", "--unwired", "bare.json"]);
+    assert_eq!(code, Some(0));
+    assert!(
+        out.contains("open slot: risk (optional, list of stop regimes { vol: { length, k } }; absent = one default regime)"),
+        "stdout/stderr: {out}"
+    );
+}
+
+/// #216: a bound (non-empty) risk list closes the slot — a complete document
+/// with risk reports no open slots at all.
+#[test]
+fn campaign_introspect_unwired_omits_a_bound_risk_slot() {
+    let dir = temp_cwd("campaign-introspect-unwired-risk-bound");
+    let with_risk = CAMPAIGN_DOC.replacen(
+        "\"seed\": 1,",
+        "\"seed\": 1,\n  \"risk\": [ { \"vol\": { \"length\": 3, \"k\": 2.0 } } ],",
+        1,
+    );
+    assert_ne!(with_risk, CAMPAIGN_DOC, "replacen must actually match the fixture's seed field");
+    write_doc(&dir, "bound.campaign.json", &with_risk);
+    let (out, code) =
+        run_code_in(&dir, &["campaign", "introspect", "--unwired", "bound.campaign.json"]);
+    assert_eq!(code, Some(0));
+    assert!(!out.contains("open slot: risk"), "bound risk must not list: {out}");
+    assert!(out.contains("no open slots"), "stdout/stderr: {out}");
+}
+
+/// #216: an EXPLICIT `"risk": []` (key present, array empty) is still an open
+/// slot — same as the key being absent entirely. The probe distinguishes
+/// "bound" from "unbound" by non-emptiness, not by key presence
+/// (`v.get("risk").and_then(|r| r.as_array()).is_some_and(|a| !a.is_empty())`);
+/// a probe that instead branched on `is_none()` would wrongly treat an
+/// explicit empty list as closed, and no other test in this file exercises
+/// that branch (the absent-key and non-empty-array cases are covered above).
+#[test]
+fn campaign_introspect_unwired_lists_the_risk_slot_when_explicitly_empty() {
+    let dir = temp_cwd("campaign-introspect-unwired-risk-explicit-empty");
+    let explicit_empty = CAMPAIGN_DOC.replacen("\"seed\": 1,", "\"seed\": 1,\n  \"risk\": [],", 1);
+    assert_ne!(explicit_empty, CAMPAIGN_DOC, "replacen must actually match the fixture's seed field");
+    write_doc(&dir, "empty-risk.campaign.json", &explicit_empty);
+    let (out, code) =
+        run_code_in(&dir, &["campaign", "introspect", "--unwired", "empty-risk.campaign.json"]);
+    assert_eq!(code, Some(0), "stdout/stderr: {out}");
+    assert!(
+        out.contains(
+            "open slot: risk (optional, list of stop regimes { vol: { length, k } }; absent = one default regime)"
+        ),
+        "an explicit empty risk array must still count as an open slot: {out}"
+    );
+}
+
 #[test]
 fn campaign_introspect_unwired_reports_the_spec_example_slots() {
     let dir = temp_cwd("campaign-introspect-unwired");