Delete the declarations' stream once every node runs the new node-engine, and assert it no more (issue 1945, B13)

A node away during the switch finds its last declaration on the stream; once every node's have names the
node-engine registered, no node reads one, so the stream and the nodes' consumers on it go, said once, and a raise
leaves them out (ADR 0539 clause 11).

cmd/mesh-controller/busobjects.go

@@ -29,7 +29,13 @@ func assertBusObjects(ctx context.Context, inv *inventory.Inventory, r broker.Ra
 	for _, n := range nodes {
 		names = append(names, n.Name)
 	}
-	if err := broker.Raise(r, names); err != nil {
+	// Once every node runs the node-engine that reads no declaration, the declarations' stream and the nodes'
+	// consumers on it are not asserted again (novox/hq ADR 0539 clause 11; composed_start.go retires them).
+	raise := func() error { return broker.Raise(r, names) }
+	if declarationsRetiredNow(ctx, inv) {
+		raise = func() error { return broker.RaiseAfterDeclarations(r) }
+	}
+	if err := raise(); err != nil {
 		return nil, err
 	}
 	// And each node's bucket for the files of its declaration that travel by digest (novox/hq ADR 0486 §4), so a node finds its own