diff --git a/crates/aura-cli/tests/research_docs.rs b/crates/aura-cli/tests/research_docs.rs
index 49e8a34..9a327c7 100644
--- a/crates/aura-cli/tests/research_docs.rs
+++ b/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");
diff --git a/docs/authoring-guide.md b/docs/authoring-guide.md
index f0d06fb..fff4f75 100644
--- a/docs/authoring-guide.md
+++ b/docs/authoring-guide.md
@@ -266,13 +266,14 @@ open slot: format_version (required, must be 1)
 open slot: kind (required, must be "campaign")
 open slot: name (required, string)
 open slot: data (required section: instruments + windows)
+open slot: risk (optional, list of stop regimes { vol: { length, k } }; absent = one default regime)
 open slot: strategies (required, non-empty list of { ref, axes })
 open slot: process.ref (required, content id of a process document)
 open slot: seed (required, non-negative integer)
 open slot: presentation (required section: persist_taps (equity | exposure | r_equity | net_r_equity) + emit)
 ```
 
-### Worked example: two instruments, one strategy, four axis points
+### Worked example: two instruments, one strategy, four axis points, two stop regimes
 
 ```json
 {
@@ -284,6 +285,10 @@ open slot: presentation (required section: persist_taps (equity | exposure | r_e
     "instruments": ["GER40", "FRA40"],
     "windows": [ { "from_ms": 1725148800000, "to_ms": 1727740800000 } ]
   },
+  "risk": [
+    { "vol": { "length": 3, "k": 1.5 } },
+    { "vol": { "length": 3, "k": 3.0 } }
+  ],
   "strategies": [
     {
       "ref": { "content_id": "597d719b7ac607158cda3e68cd497387620397a5e93087e23da512876dafba9a" },
@@ -306,11 +311,17 @@ Each axis name (`fast.length`, …) must name an open param of the referenced
 blueprint (`aura graph introspect --params`, §1) and declare that param's
 `ScalarKind`.
 
+The optional `risk` list is the campaign's structural risk axis: every cell
+runs under every listed stop regime, so cells differ by execution discipline,
+never by signal — the regime's stop defines the risk unit R. Absent or empty,
+the matrix runs one implicit default regime (the same vol regime the
+orchestration verbs bind when their stop flags are omitted).
+
 ### Validate — three tiers, honest degradation
 
 ```
 $ aura campaign validate mra_3_campaign_full_v2.json          # outside any project
-campaign document valid (intrinsic): 1 strategy(ies), 3 axes (4 points), 1 window(s)
+campaign document valid (intrinsic): 1 strategy(ies), 3 axes (4 points), 2 instrument(s), 1 window(s), 2 regime(s) — 4 cell(s)
 referential checks skipped (no Aura.toml found up from /home/…)
 ```
 
@@ -319,7 +330,7 @@ registered, the same command runs two further tiers:
 
 ```
 $ aura campaign validate mra_3_campaign_full_v2.json          # inside a project, refs registered
-campaign document valid (intrinsic): 1 strategy(ies), 3 axes (4 points), 1 window(s)
+campaign document valid (intrinsic): 1 strategy(ies), 3 axes (4 points), 2 instrument(s), 1 window(s), 2 regime(s) — 4 cell(s)
 campaign document valid (referential): all references resolve, axes are in the param space
 campaign document valid (executable): pipeline shape and static guards pass
 ```
diff --git a/docs/glossary.md b/docs/glossary.md
index deba6ea..15861a4 100644
--- a/docs/glossary.md
+++ b/docs/glossary.md
@@ -211,6 +211,14 @@ The per-symbol composite turning a bias into a managed position, **in R**: `stop
 **Avoid:** —
 A node that converts a finer stream to a coarser bar stream, emitting a completed bar only at the boundary so no partial bar ever leaks (enforcing no look-ahead). Clock-sensitive.
 
+### risk regime
+**Avoid:** stop regime, risk section
+One entry of a campaign document's structural risk axis (`risk`): a
+serializable protective-stop regime (sole variant `vol{length,k}`) the matrix
+runs every cell under, so cells differ by execution discipline, never by
+signal. Absent or empty = one implicit default regime; the regime's stop
+defines the risk unit R.
+
 ### run
 **Avoid:** —
 One execution recorded in the run registry as a manifest + metrics — the registry-record framing of an execution. Distinct from `sim` (the executable unit) and `backtest` (the replay framing).