Judge the SDK conformance fixtures against the SDK the controller pins, never a desktop's checkout (issue 449)

A check clones mesh-sdk beside the controller at the commit go.mod pins; elsewhere
the test reads a copy captured at that commit, held to go.mod. A missing clone fails
instead of skipping.

testdata/beside/CAPTURED

@@ -9,6 +9,7 @@ a second place to clean besides the catalogue itself.
 
 mesh-catalog  b9de001833b1b61b297182b8e3bcdae1cbdeace9  modules/*/module.json, modules/nats/Dockerfile
 mesh-host     bd5cc6980419c1bd4824be6d58dfebd2381a9de3  examples/foundation-first-node-nats.lock
+mesh-sdk      f047d0a4a9702f5d7f3d7eadd3e62496311acc00  conformance/events/module-event.json
 
 To move them, from this repository's root, with the two repositories checked out beside it:
 
@@ -19,4 +20,8 @@ To move them, from this repository's root, with the two repositories checked out
   find testdata/beside -name module.json -exec mv {} {}.captured \;
   git -C ../mesh-host archive <commit> examples/foundation-first-node-nats.lock | tar -x -C testdata/beside/mesh-host
 
-and write the commits here.
+and write the commits here. The SDK is captured at the commit go.mod pins for git.novox.be/novox/mesh-sdk/go
+(the last part of its pseudo-version; novox/hq issue 449), which internal/link's conformance test holds it to:
+
+  rm -rf testdata/beside/mesh-sdk && mkdir -p testdata/beside/mesh-sdk
+  git -C ../mesh-sdk archive <commit> conformance/events | tar -x -C testdata/beside/mesh-sdk

testdata/beside/mesh-sdk/conformance/events/module-event.json

@@ -0,0 +1,44 @@
+{
+  "capability": "events",
+  "name": "a module emits an event",
+  "why": "The envelope is what two implementations can disagree about without either failing: a missing header, a header spelled differently, or a body nested where metadata belongs. None of those stop a mesh running; they stop it reacting.",
+  "given": {
+    "module": "shop",
+    "node": "one",
+    "key": "order.placed",
+    "body": { "id": "a1", "total": 12 },
+    "headers": {
+      "x-event-id": "0123456789abcdef0123456789abcdef",
+      "x-source": "shop",
+      "x-node": "one",
+      "x-time": "2026-09-26T12:00:00Z",
+      "content-type": "application/json"
+    }
+  },
+  "wire": {
+    "subject": "mesh.mod.shop.event.order.placed",
+    "requiredHeaders": ["x-event-id", "x-source", "x-node", "x-time", "content-type"],
+    "optionalHeaders": ["x-causation-id", "x-schema"],
+    "headerFormats": {
+      "x-time": "RFC3339",
+      "content-type": "application/json",
+      "x-event-id": "^[0-9a-f]{32}$"
+    },
+    "payloadIs": "the body alone, not the envelope",
+    "keyRecoveredFrom": "the subject, after the .event. token"
+  },
+  "refuses": [
+    {
+      "what": "an envelope nested in the payload",
+      "why": "an implementation that publishes the whole envelope as the body passes all of its own tests and is unreadable to every other"
+    },
+    {
+      "what": "a missing x-event-id",
+      "why": "delivery is at-least-once and only the emitter can say which of two messages is a redelivery"
+    },
+    {
+      "what": "an x-source that differs from the subject's module",
+      "why": "the bus enforces the namespace, so a disagreement means the envelope is lying about its origin"
+    }
+  ]
+}