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).

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
 ```