The build role is the node-scoped seat node-build-agent, and its work is shared by every holder (hq ADR 0190)

One build machine built everything, in a queue of one, because the seat was mesh-scoped and a
mesh seat has one holder. ADR 0190 makes building a node role: node-build-agent, held on every
machine that builds, with the work asked of the role and taken by whichever holder is idle. The
work subject of a node-scoped seat carries no node — that token is for a seat's tools, asked of
one machine (design 33 §4) — so holders on several machines read one queue; a test now says so.

The retired mesh-build-machine row stays while the builder module's registered manifest claims
it: a claim to a seat the mesh no longer defines is refused, and the machine holding it would be
unresolvable until build-agent replaces it. Removed once no manifest claims it.

The installer's genesis template (in the host's repository) still grants the controller the old
seat's subjects; its test here says so until that template names node-build-agent.

internal/catalogue/seats_test.go

@@ -44,9 +44,10 @@ func TestTheSeatsAreAClosedSetAndEachNamesItsDecision(t *testing.T) {
 			delivered[s.Delivers] = s.Name
 		}
 	}
-	// Sixteen since node-service-manager (novox/hq ADR 0177).
-	if len(Seats()) != 16 {
-		t.Errorf("the mesh defines %d seats rather than 16; the set is closed, so a change here is "+
+	// Seventeen since node-build-agent (novox/hq ADR 0190) — sixteen once the retired
+	// mesh-build-machine row goes, when no registered manifest claims it any more.
+	if len(Seats()) != 17 {
+		t.Errorf("the mesh defines %d seats rather than 17; the set is closed, so a change here is "+
 			"a decision (novox/hq ADR 0110): %s", len(Seats()), seatNames())
 	}
 }