Order a branch's plans by its merges, and build the newest commit (hq issue 349)

A merge acted on late by the catch-up made its plan after the plan of the
merge that followed it, superseded it by creation time, and folded its
unbuilt modules into a plan at the older commit: on 2026-10-09 the
forge's security fix (a082615b) was superseded by 8ff8197a. A plan now
keeps its merge time (migration 0086), supersession follows it, and a
merge older than an open plan of its branch is planned at that plan's
commit, which contains it.

cmd/mesh-controller/release_plan.go

@@ -188,11 +188,13 @@ func planOfMerge(m link.SourceMoved, moved []string, edges []inventory.Edge) inv
 	for _, name := range set {
 		modules[name] = &inventory.PlanModule{}
 	}
+	merged, _ := time.Parse(time.RFC3339, m.MergedAt)
 	return inventory.Plan{
 		ID:         fmt.Sprintf("plan-%d", time.Now().UnixNano()),
 		Repository: m.Owner + "/" + m.Repo,
 		Branch:     m.Base,
 		Commit:     m.Commit,
+		Merged:     merged.UTC(),
 		Created:    time.Now().UTC(),
 		State:      inventory.PlanBuilding,
 		Tiers:      tiers,
@@ -220,12 +222,20 @@ func planOfMerge(m link.SourceMoved, moved []string, edges []inventory.Edge) inv
 //
 // A plan with no branch recorded is from before branches were kept, and is superseded by the next
 // plan of its repository: what it had not built is folded in, so nothing is lost by it.
+//
+// **Newer is the branch's order, not the plans'** (novox/hq issue 349). A merge the bus did not hand
+// over is acted on late, by the catch-up, so its plan is made after the plan of a merge that came after
+// it — and that later-made plan of the earlier commit superseded the later merge's, and built what it
+// folded in from the commit before the later merge: twice on 2026-10-09, once a security fix. So where
+// both plans know when their merge was made, that decides; only where one does not do the plans' own
+// times. A merge older than an open plan of its branch never reaches here at its own commit: it is
+// planned at the newest open plan's commit, which contains it (newestOnTheBranch).
 func supersededBy(newer inventory.Plan, open []inventory.Plan, rollsOut func(string) bool) ([]string, []inventory.Plan) {
 	folded := map[string]bool{}
 	var closed []inventory.Plan
 	for _, old := range open {
 		if old.ID == newer.ID || !old.Open() || !strings.EqualFold(old.Repository, newer.Repository) ||
-			(old.Branch != "" && old.Branch != newer.Branch) || !old.Created.Before(newer.Created) {
+			(old.Branch != "" && old.Branch != newer.Branch) || !earlierOnTheBranch(old, newer) {
 			continue
 		}
 		var took []string
@@ -254,6 +264,39 @@ func supersededBy(newer inventory.Plan, open []inventory.Plan, rollsOut func(str
 	return out, closed
 }
 
+// earlierOnTheBranch says plan a answers a merge made before b's: by when the forge made each merge where
+// both are known, else by when each plan was made. A merge's own plan made again at the same commit
+// (the same merge time) is ordered by when it was made. Pure.
+func earlierOnTheBranch(a, b inventory.Plan) bool {
+	if !a.Merged.IsZero() && !b.Merged.IsZero() && !a.Merged.Equal(b.Merged) {
+		return a.Merged.Before(b.Merged)
+	}
+	return a.Created.Before(b.Created)
+}
+
+// newestOnTheBranch is the open plan of m's repository and branch whose merge was made after m's, the
+// newest of them; false when none was. Merges into one branch are made one on the other, so that plan's
+// commit contains m's change: m is planned there, and the newest commit of the branch is what is built
+// (novox/hq issue 349). Pure.
+func newestOnTheBranch(m link.SourceMoved, open []inventory.Plan) (inventory.Plan, bool) {
+	merged, err := time.Parse(time.RFC3339, m.MergedAt)
+	if err != nil {
+		return inventory.Plan{}, false
+	}
+	var newest inventory.Plan
+	found := false
+	for _, p := range open {
+		if !p.Open() || p.Release != nil || p.Merged.IsZero() || !strings.EqualFold(p.Repository, m.Owner+"/"+m.Repo) ||
+			p.Branch != m.Base || !p.Merged.After(merged) {
+			continue
+		}
+		if !found || p.Merged.After(newest.Merged) {
+			newest, found = p, true
+		}
+	}
+	return newest, found
+}
+
 // gates is what the next tier needs running from this one: a module of the tier that a later
 // tier is built by — the runtime dependency — and whose policy rolls it out, must be applied by
 // the machines running it before the next tier is asked. A base an image stands on need only be