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,

cmd/mesh-controller/checks_test.go

@@ -260,3 +260,21 @@ func TestABuildOfACheckMergeIsRefusedNamingTheTrunk(t *testing.T) {
 		t.Fatalf("a build of a check's merge was answered %v", err)
 	}
 }
+
+// **A verdict no build judges names its trunk commit too** (novox/hq ADR 0323 §3): a change touching no module of a
+// repository with no merge-check.sh (novox/mesh-tools-go) is answered by the controller itself. Naming no trunk, the
+// merge tool refused it, asked again, got the same verdict, and refused for ever.
+func TestADirectVerdictNamesTheTrunkTheForgeAnnounced(t *testing.T) {
+	p := link.PullUpdated{Owner: "novox", Repo: "mesh-tools-go", Number: 3, Base: "main", Commit: "1a2b3c4d5e6f7a8b9c0d",
+		BaseSHA: "7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b"}
+	c := directVerdict(p, link.ChangePlan{Repository: "novox/mesh-tools-go", Base: "main", Head: p.Commit})
+	if c.Trunk != "7a8b9c0d1e2f" || c.Plan == nil || c.Plan.Trunk != "7a8b9c0d1e2f" {
+		t.Fatalf("the direct verdict names trunk %q, its plan %+v", c.Trunk, c.Plan)
+	}
+	if c.Verdict != "pass" || c.Commit != p.Commit {
+		t.Fatalf("the direct verdict is %+v", c)
+	}
+	if c := directVerdict(link.PullUpdated{Owner: "novox", Repo: "x", Commit: "abc"}, link.ChangePlan{}); c.Trunk != "" {
+		t.Fatalf("a forge that said no base head gave the trunk %q", c.Trunk)
+	}
+}

internal/link/events.go

@@ -228,6 +228,10 @@ type PullUpdated struct {
 	Base     string `json:"base"`
 	Head     string `json:"head"`
 	Commit   string `json:"head_sha"`
+	// BaseSHA is the base branch's head when the forge announced the head (novox/hq ADR 0323): the trunk commit a
+	// verdict the controller gives without the build seat — a change that runs no build — is judged against. Empty
+	// from a forge module from before it.
+	BaseSHA string `json:"base_sha,omitempty"`
 	CloneURL string `json:"clone_url"`
 	HTMLURL  string `json:"html_url,omitempty"`
 	// Paths are the files the pull request changes; PathsTruncated says there were more.