Name the announced trunk commit on a verdict no build judges

A change touching no module, in a repository with no merge-check.sh, was
answered by the controller with no trunk commit, so the merge tool refused it,
asked again and refused it for ever (novox/mesh-tools-go; novox/hq ADR 0323).

cmd/mesh-controller/checks.go

@@ -161,9 +161,7 @@ func (f following) PullUpdated(ctx context.Context, p link.PullUpdated) error {
 		return u, err == nil
 	})
 	fmt.Print(planText(plan))
-	direct := link.Checked{Owner: p.Owner, Repo: p.Repo, Number: p.Number, Commit: p.Commit,
-		ID: link.NewBuildID(time.Now()), Verdict: "pass", Summary: noModuleTouched,
-		Gate: &link.CheckLayer{Verdict: "pass", Summary: noModuleTouched}, Plan: &plan}
+	direct := directVerdict(p, plan)
 	switch {
 	case !scope.gated() && !scope.Mesh:
 		fmt.Printf("%s/%s#%d (%.8s): %s, and the repository is not the mesh's: said, nothing run\n",
@@ -201,6 +199,24 @@ func (f following) PullUpdated(ctx context.Context, p link.PullUpdated) error {
 	return nil
 }
 
+// directVerdict is the verdict of a change no build judges — it touches no module, and either the repository is not
+// the mesh's or the head holds no merge-check.sh. **It names the trunk commit it holds for** (novox/hq ADR 0323 §3):
+// the base branch's head the forge announced with the head, so the merge tool can weigh it against the trunk's head
+// and does not refuse it for ever (a verdict naming no trunk is never the trunk's head's). Nothing was built to
+// judge: the trunk commit is the one the forge said the change was announced against.
+func directVerdict(p link.PullUpdated, plan link.ChangePlan) link.Checked {
+	trunk := p.BaseSHA
+	if len(trunk) > 12 {
+		trunk = trunk[:12]
+	}
+	if trunk != "" {
+		plan.Trunk = trunk
+	}
+	return link.Checked{Owner: p.Owner, Repo: p.Repo, Number: p.Number, Commit: p.Commit,
+		ID: link.NewBuildID(time.Now()), Verdict: "pass", Summary: noModuleTouched,
+		Gate: &link.CheckLayer{Verdict: "pass", Summary: noModuleTouched}, Plan: &plan, Trunk: trunk}
+}
+
 // checkRequestFor is the ask for one pull request's head: the repository as the mesh clones it, the head,
 // and what is read beside it.
 func checkRequestFor(ctx context.Context, open *stores, p link.PullUpdated, scope checkScope,