Fix 9.5: the seat node-build-image's build acting rule acts on kind:image

Builds: design 47 G §324, §397

Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h

contracts/go/seats/nodebuildimage/acts_test.go

@@ -0,0 +1,24 @@
+package nodebuildimage
+
+import (
+	"encoding/json"
+	"os"
+	"testing"
+)
+
+// The seat's `build` acting rule matches an artifact by its kind, an image having no language (design 47 G §324, §397).
+func TestTheSeatsBuildRuleActsOnTheKindImage(t *testing.T) {
+	raw, err := os.ReadFile("../../../seats/node-build-image/seat.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var def struct {
+		Acts []struct{ Step, On, Bound string } `json:"acts"`
+	}
+	if err := json.Unmarshal(raw, &def); err != nil {
+		t.Fatal(err)
+	}
+	if len(def.Acts) != 1 || def.Acts[0].Step != "build" || def.Acts[0].On != "kind:image" {
+		t.Errorf("acts = %+v; wanted the one rule {build, kind:image}", def.Acts)
+	}
+}

contracts/seats/node-build-image/seat.json

@@ -7,6 +7,13 @@
   "decision": "novox/hq ADR 0525, ADR 0536, ADR 0553",
   "pulled-by-kind": true,
   "yields": true,
+  "acts": [
+    {
+      "step": "build",
+      "on": "kind:image",
+      "bound": "60m"
+    }
+  ],
   "accepts": [
     {
       "name": "delivery",