SD-M2b sdk: a seat's event family may name its own subject token

The lead's ruling of 12:5x (design 25 § 12.3): mesh-broker's events ride the bus module's own stream, 30 days,
on mesh.seat.mesh-broker.said.<event>, outside the shared events stream's mesh.seat.*.event.>, so the bus never
refuses the two as overlapping.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

go/buscompose/names_test.go

@@ -1,8 +1,10 @@
 package buscompose
 
 import (
+	"strings"
 	"testing"
 
+	"git.novox.be/novox/mesh-contracts/go/seats/meshbroker"
 	"git.novox.be/novox/mesh-sdk/go/membership"
 )
 
@@ -32,4 +34,27 @@ func TestTheBusNamesAgree(t *testing.T) {
 	if err := ledger.Valid(); err != nil || ledger.OwnSecret() != "ledgers" {
 		t.Fatalf("a wanted ledger account: %v, held in %q", err, ledger.OwnSecret())
 	}
+	// mesh-broker's events are the bus module's own stream (design 25 § 12.3, 30 days): no subject of the shared
+	// streams may take them, or the bus refuses the two streams as overlapping.
+	for _, st := range MeshStreams() {
+		for _, pattern := range st.Subjects {
+			if subjectTakes(pattern, meshbroker.SubjectCreated) {
+				t.Errorf("the stream %s takes mesh-broker's %s by %s", st.Name, meshbroker.SubjectCreated, pattern)
+			}
+		}
+	}
+}
+
+// subjectTakes says whether a subject pattern (`*` one token, `>` the rest) takes a subject.
+func subjectTakes(pattern, subject string) bool {
+	p, s := strings.Split(pattern, "."), strings.Split(subject, ".")
+	for i, tok := range p {
+		switch {
+		case tok == ">":
+			return len(s) > i
+		case i >= len(s) || (tok != "*" && tok != s[i]):
+			return false
+		}
+	}
+	return len(p) == len(s)
 }