Assemble merges in a rolling window and walk each batch once (hq ADR 0276, issue 362)

Every merge opened a walk and the next merge of the branch superseded it: two
catalogue merges 18 s apart left a walk no delivery held, and the operator
started it by hand 58 minutes later. A merge now joins the open batch, kept in
the store (migration 0089), which is cut into one walk when no merge came for
merge-window (90 s) or at merge-window-at-most (10 min): one commit per
repository, the latest of its branch, with every file the batch's merges
changed. One walk at a time; a started walk is never superseded, a waiting one
is folded into the next. The walk names every merge it answers on the wire
(delivery.merges, taken_over_by, batch). A failed walk walks its earlier merges
alone, newest first, until one is delivered. A delivery group's order becomes
tier edges inside the walk. plans shows the batch assembling; S18 and S19
bound its waits; S16 names the merges a waiting walk answers.

cmd/mesh-controller/delivery.go

@@ -574,6 +574,12 @@ func deliveryCommand(ctx context.Context, args []string) error {
 			if walks, err = inv.OpenPlans(ctx); err != nil {
 				return err
 			}
+			// And the batch being assembled (novox/hq ADR 0276): never a walk to link or let go, shown.
+			batches, err := inv.Batches(ctx)
+			if err != nil {
+				return err
+			}
+			walks = append(walks, batches...)
 			recent, err := inv.RecentPlans(ctx, *limit)
 			if err != nil {
 				return err