Give each node a bucket of its own for the files that travel by digest, and keep the sweep from removing an object a send relies on (issues 1696, 1697; review of ADR 0486 step 3)

A literal * in a published subject matches the grant's *, so in one shared bucket a node could read every node's files. Each node now
has declaration-files-<node>, which its account reads by name and the controller writes; the sweep judges each bucket against that
node's latest declaration, under the node's lock with the send, and an object the sweep marked is put again by the next send. Putting
that fails send after send raises a condition.

cmd/mesh-controller/busobjects.go

@@ -32,6 +32,13 @@ func assertBusObjects(ctx context.Context, inv *inventory.Inventory, r broker.Ra
 	if err := broker.Raise(r, names); 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
+	// whenever the bus is up.
+	if files, ok := r.(interface{ EnsureDeclarationFiles(nodes []string) error }); ok {
+		if err := files.EnsureDeclarationFiles(names); err != nil {
+			return nil, err
+		}
+	}
 	// The work queues of the mesh's own roles (novox/hq ADR 0121). The queue before the holder,
 	// deliberately: work queues until somebody arrives to do it, so assigning a build machine a week
 	// after something started asking for builds flushes the backlog instead of having lost it.