A late merge is named however its modules read since the cut; a walk builds the commits it carries (hq ADR 0276 review)

cmd/mesh-controller/release_plan.go

@@ -330,8 +330,15 @@ func askModule(ctx context.Context, p *inventory.Plan, name string, byName map[s
 	}
 	source := buildSource{Repository: e.Source.Repository, Seat: e.Source.Seat}
 	fmt.Printf("  tier %d: ", p.Tier)
-	// The branch it follows, never a commit a build once named (novox/hq 04-ISSUES/215).
-	id, err := askABuild(ctx, source, e.Source.Path, followedBranch(e.Source.Ref))
+	// The branch it follows, never a commit a build once named (novox/hq 04-ISSUES/215) — but for the commit a
+	// batch's walk carries of the module's own repository and branch (novox/hq ADR 0276): the walk builds what
+	// it answers, not a merge heard after it was cut, and a merge walked alone is built on its own commit.
+	ref := followedBranch(e.Source.Ref)
+	carried := p.CommitOn(e.Source.Repository, ref)
+	if len(p.Commits) > 0 && carried != "" {
+		ref = carried
+	}
+	id, err := askABuild(ctx, source, e.Source.Path, ref)
 	if err != nil {
 		state.State = "failed"
 		state.Why = err.Error()
@@ -341,7 +348,7 @@ func askModule(ctx context.Context, p *inventory.Plan, name string, byName map[s
 	}
 	// The commit of the module's own repository the walk carries (novox/hq ADR 0276): a batch's walk carries
 	// one per repository.
-	commit := p.CommitOf(e.Source.Repository)
+	commit := carried
 	if commit == "" {
 		commit = p.Commit
 	}