Send files over 64 KiB by digest through the bus's object bucket to nodes that read them, grant it, and warn at 75 percent (issues 1696, 1697, 1698; ADR 0486 step 3)

A node that reports file-references gets the digest and size of each file over 64 KiB that may travel so, and the content is put in
the bucket declaration-files before the declaration is sent; others get every content inline. The controller alone writes the
bucket and node-engines read an object by name (the four grants the node-engine's own fetch makes, no list, no write). An object
goes a day after no node's latest declaration names it. The near-limit condition warns at 75 percent, and a test holds the control
node's declaration, in the reference form, under half the bus's largest message.

cmd/mesh-controller/push.go

@@ -282,6 +282,8 @@ func serve(ctx context.Context) (err error) {
 	// assignment.
 	inv.SetProvisioningPlans(inv.SentProvisioningPlans)
 	go mirroringRecords(ctx, inv, bus.Conn, bus)
+	// And the bucket of the files that travel by digest, judged against what each machine's latest declaration names (ADR 0486 §3).
+	go sweepingDeclarationFiles(ctx, inv, bus.Conn)
 	// Every call carries the lease's epoch, and its record is written only under the lease (novox/hq
 	// to-be 45 §6).
 	link.Calls.UnderLease(func() (uint64, error) { return theLease.epoch(ctx) })
@@ -979,6 +981,18 @@ func deliver(ctx context.Context, d delivery, holder string, sending []readyNode
 			return err
 		}
 		digest, err := d.declare(ctx, s, body)
+		if errors.Is(err, errFilesNotPut) && s.declared.fileReferences {
+			// **The grant that lets the controller write the bucket travels in the very declaration of the machine holding the
+			// bus** (novox/hq ADR 0486 §2): until the bus has it, a put is refused, and the declaration that would deliver the
+			// grant would wait for it. So that send, and only that, goes with every content inline, as to a node that reads no
+			// references, and says so; the next one tries the bucket again.
+			fmt.Printf("%s: the files that travel by digest could not be put in the bucket (%v): sending them inline\n", s.node, err)
+			s.declared.fileReferences = false
+			if body, err = s.declared.Body(); err != nil {
+				return err
+			}
+			digest, err = d.declare(ctx, s, body)
+		}
 		if err != nil {
 			return err
 		}
@@ -1040,6 +1054,34 @@ type overTheBus struct {
 	indent string
 }
 
+// putFiles puts the contents s names by digest in the bucket.
+func (b overTheBus) putFiles(ctx context.Context, s readyNode) error {
+	objects, err := s.declared.objects()
+	if err != nil {
+		return fmt.Errorf("%s: the files that travel by digest cannot be read: %w", s.node, err)
+	}
+	if len(objects) == 0 {
+		return nil
+	}
+	bus, ok := b.server.Bus().(link.OverNATS)
+	if !ok {
+		return fmt.Errorf("%s: the declaration names files by digest and this bus has no object bucket", s.node)
+	}
+	store, err := openBucket(ctx, bus.Conn)
+	if err != nil {
+		return fmt.Errorf("%s was not sent its declaration: %w: %w", s.node, errFilesNotPut, err)
+	}
+	putting, cancel := context.WithTimeout(ctx, 30*time.Second)
+	defer cancel()
+	if err := putObjects(putting, store, objects); err != nil {
+		return fmt.Errorf("%s was not sent its declaration: %w: %w", s.node, errFilesNotPut, err)
+	}
+	return nil
+}
+
+// errFilesNotPut marks a send that stopped because the files it names by digest could not be put in the bucket.
+var errFilesNotPut = errors.New("the files it names by digest are not in the bucket")
+
 func (b overTheBus) grant(ctx context.Context, sending []readyNode) error {
 	// The bus's objects first, which every declaration implies (novox/hq issue 208): said and raised
 	// when they cannot be, and never what holds the send back (assertOnSend).
@@ -1052,6 +1094,11 @@ func (b overTheBus) grant(ctx context.Context, sending []readyNode) error {
 }
 
 func (b overTheBus) declare(ctx context.Context, s readyNode, body []byte) (string, error) {
+	// The contents the declaration names by digest are in the bucket before it is sent (novox/hq ADR 0486 §1, issue 1696): a node
+	// that applies it finds every one. A node reading no references has none.
+	if err := b.putFiles(ctx, s); err != nil {
+		return "", err
+	}
 	if err := link.Declare(ctx, b.server.Bus(), b.signer, s.node, body, 15*time.Second); err != nil {
 		return "", err
 	}