Let a newer plan supersede the older open plans of its repository (hq issue 254, ADR 0218)

A merge planned without looking at open plans, so two plans worked the
same modules and a stuck plan stayed open for ever. The newer plan folds
in what older plans of the same repository and branch had not built or
sent, and closes them as superseded. A person can close a stuck plan by
id with `plans close <id>`.

cmd/mesh-controller/upgrades.go

@@ -324,6 +324,45 @@ func (f following) SourceMoved(ctx context.Context, m link.SourceMoved) error {
 	}
 	defer release()
 	plan := planOfMerge(m, movedNames, edges)
+	// **A newer plan supersedes the older open plans of this repository and branch** (novox/hq issue
+	// 254, ADR 0218): what they had not built is planned here again, and they are closed, so one plan
+	// works a repository's modules at a time and a stuck one ends at the next merge.
+	working, err := inv.OpenPlans(ctx)
+	if err != nil {
+		return notNow(err)
+	}
+	rollsOut := func(module string) bool {
+		u, err := inv.UpgradeOf(ctx, module)
+		return err == nil && u.RollOut
+	}
+	folded, superseded := supersededBy(plan, working, rollsOut)
+	if len(folded) > 0 {
+		held := map[string]bool{}
+		for _, e := range entries {
+			held[e.Manifest.Module] = true
+		}
+		names := map[string]bool{}
+		for _, name := range movedNames {
+			names[name] = true
+		}
+		var also []string
+		for _, name := range folded {
+			// One the catalogue no longer holds would fail the newer plan's ask; it is not this
+			// merge's to build.
+			if held[name] && !names[name] {
+				names[name] = true
+				movedNames = append(movedNames, name)
+				also = append(also, name)
+			}
+		}
+		if len(also) > 0 {
+			again := planOfMerge(m, movedNames, edges)
+			again.ID, again.Created = plan.ID, plan.Created
+			plan = again
+			fmt.Printf("  %s, left unbuilt by an older plan of %s, are planned here again\n",
+				strings.Join(also, ", "), plan.Repository)
+		}
+	}
 	if hasCycle(plan.Tiers, edges) {
 		fmt.Printf("  the last tier depends on itself: %s — built together, in no order\n",
 			strings.Join(plan.Tiers[len(plan.Tiers)-1], ", "))
@@ -331,6 +370,14 @@ func (f following) SourceMoved(ctx context.Context, m link.SourceMoved) error {
 	if err := inv.SavePlan(ctx, plan); err != nil {
 		return notNow(err)
 	}
+	// Closed after the newer plan is kept, never before: a controller replaced between the two leaves
+	// both open, which the next merge settles, rather than neither.
+	for _, old := range superseded {
+		if err := inv.SavePlan(ctx, old); err != nil {
+			return notNow(err)
+		}
+		fmt.Printf("  %s (%s at %s) is %s\n", old.ID, old.Repository, short(old.Commit), old.Note)
+	}
 	var tiers []string
 	for i, t := range plan.Tiers {
 		tiers = append(tiers, fmt.Sprintf("%d: %s", i, strings.Join(t, ", ")))