diff --git a/cmd/mesh-controller/batches.go b/cmd/mesh-controller/batches.go
index 81a52afb..165bdb42 100644
--- a/cmd/mesh-controller/batches.go
+++ b/cmd/mesh-controller/batches.go
@@ -177,7 +177,7 @@ func (f following) hearMerge(ctx context.Context, m link.SourceMoved, now time.T
 				repository, m.Base, m.Commit, already)
 			return nil
 		}
-		fmt.Printf("%s merged into %s (%.8s); nothing the mesh holds reads it\n", repository, m.Base, m.Commit)
+		fmt.Print(nothingReadsIt(repository, m))
 		return nil
 	}
 	// **Its delivery group's word, before the plans are held** (ADR 0306 decision 2): a slow answer holds up no walk.
diff --git a/cmd/mesh-controller/non_trunk_merge_test.go b/cmd/mesh-controller/non_trunk_merge_test.go
new file mode 100644
index 00000000..3e7c190d
--- /dev/null
+++ b/cmd/mesh-controller/non_trunk_merge_test.go
@@ -0,0 +1,53 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/catalogue"
+	"github.com/novox/mesh-controller/internal/inventory"
+)
+
+// A merge into a branch other than the trunk starts no delivery (novox/hq ADR 0401 clause 3, issue 889): a
+// module recorded with no ref follows the trunk, main, and no other branch.
+func TestAMergeIntoANonTrunkBranchStartsNoDelivery(t *testing.T) {
+	for ref, name := range map[string]string{"": "noref", "main": "mainref"} {
+		t.Run(name, func(t *testing.T) {
+			open := windowed(t)
+			asksWithPaths(t)
+			if err := open.inventory.RegisterModule(t.Context(), catalogue.Manifest{Module: "free", Version: "1"},
+				inventory.Source{Repository: "novox/free", Seat: "git", Ref: ref, BuiltFrom: "c0", Head: "c0"}); err != nil {
+				t.Fatal(err)
+			}
+			feature := lone(repoMerge("free", "f1", t0))
+			feature.Base = "feat/57-config-and-provisioning"
+			said := captured(t, func() error { return (following{open: open}).hearMerge(t.Context(), feature, t0) })
+			if ws, bs := walks(t, open); len(ws) != 0 || len(bs) != 0 {
+				t.Fatalf("a merge into a feature branch: %d walk(s), %d batch(es)", len(ws), len(bs))
+			}
+			if !strings.Contains(said, feature.Base) || !strings.Contains(said, "starts no delivery") {
+				t.Fatalf("the merge was not said to start no delivery: %q", said)
+			}
+			hear(t, open, lone(repoMerge("free", "m1", t0)), t0)
+			if ws, bs := walks(t, open); len(ws)+len(bs) != 1 {
+				t.Fatalf("a merge into main: %d walk(s), %d batch(es)", len(ws), len(bs))
+			}
+		})
+	}
+}
+
+// A module recorded with an explicit branch keeps following that branch (the lead's settlement of issue 977 Q5).
+func TestAModuleRecordedWithABranchStillFollowsIt(t *testing.T) {
+	open := windowed(t)
+	asksWithPaths(t)
+	if err := open.inventory.RegisterModule(t.Context(), catalogue.Manifest{Module: "pinned", Version: "1"},
+		inventory.Source{Repository: "novox/pinned", Seat: "git", Ref: "feat/x", BuiltFrom: "c0", Head: "c0"}); err != nil {
+		t.Fatal(err)
+	}
+	m := lone(repoMerge("pinned", "p1", t0))
+	m.Base = "feat/x"
+	hear(t, open, m, t0)
+	if ws, bs := walks(t, open); len(ws)+len(bs) != 1 {
+		t.Fatalf("a merge into the branch a module follows: %d walk(s), %d batch(es)", len(ws), len(bs))
+	}
+}
diff --git a/cmd/mesh-controller/upgrades.go b/cmd/mesh-controller/upgrades.go
index 31626b80..ea9ec498 100644
--- a/cmd/mesh-controller/upgrades.go
+++ b/cmd/mesh-controller/upgrades.go
@@ -326,8 +326,7 @@ func movesOfMerge(ctx context.Context, inv *inventory.Inventory, m link.SourceMo
 				"from it\n", m.Owner, m.Repo, m.Base, m.Commit, already)
 			return nil, nil
 		}
-		fmt.Printf("%s/%s merged into %s (%.8s); nothing the mesh holds reads it\n",
-			m.Owner, m.Repo, m.Base, m.Commit)
+		fmt.Print(nothingReadsIt(m.Owner+"/"+m.Repo, m))
 		return nil, nil
 	}
 	// Said, never silent (novox/hq 04-ISSUES/215): a module built from this repository that follows
@@ -531,7 +530,7 @@ func whyMoved(e inventory.Entry, read []inventory.ReadRepository, m link.SourceM
 		return "read whole: " + whole
 	}
 	for _, r := range read {
-		if r.Own || !sameRepository(r.Repository, m) || (r.Ref != "" && r.Ref != m.Base) {
+		if r.Own || !sameRepository(r.Repository, m) || !followsBase(r.Ref, m.Base) {
 			continue
 		}
 		if len(r.Paths) > 0 {
@@ -615,6 +614,17 @@ func retireDeleted(ctx context.Context, inv *inventory.Inventory, e inventory.En
 	}
 }
 
+// nothingReadsIt is what is said of a merge no module the mesh holds reads. **A merge into a branch other than the
+// trunk is said to start no delivery** (novox/hq ADR 0401 clause 3, issue 889): every delivery is cut from a
+// repository's trunk, and whoever merged into a feature branch should not look for a broken trigger.
+func nothingReadsIt(repository string, m link.SourceMoved) string {
+	if m.Base != "" && m.Base != "main" {
+		return fmt.Sprintf("%s merged into %s (%.8s), not the trunk of %s; a merge into any other branch starts no "+
+			"delivery\n", repository, m.Base, m.Commit, repository)
+	}
+	return fmt.Sprintf("%s merged into %s (%.8s); nothing the mesh holds reads it\n", repository, m.Base, m.Commit)
+}
+
 // sourceIs is whether a recorded source is the repository and branch a merge announced. A source on
 // the git seat is recorded as its path on the forge; one elsewhere as the URL it was cloned from.
 // An empty recorded ref is the repository's default branch, which is what a merge into the base
@@ -623,8 +633,18 @@ func sourceIs(s inventory.Source, m link.SourceMoved) bool {
 	if !sameRepository(s.Repository, m) {
 		return false
 	}
-	ref := followedBranch(s.Ref)
-	return ref == "" || ref == m.Base
+	return followsBase(s.Ref, m.Base)
+}
+
+// followsBase is whether a recorded ref follows the branch a merge went into. **An empty ref is the
+// trunk, main, and nothing else** (novox/hq ADR 0401 clause 3, issue 889): it used to match a merge
+// into any branch, so a merge into a feature branch started a delivery. A ref recorded as a branch
+// keeps following that branch.
+func followsBase(ref, base string) bool {
+	if ref = strings.TrimSpace(followedBranch(ref)); ref == "" {
+		ref = "main"
+	}
+	return ref == base
 }
 
 // commitRef is a ref that names a commit rather than a branch: what `build --ref <commit>` asks for.
@@ -663,7 +683,7 @@ func sameRepository(repository string, m link.SourceMoved) bool {
 // read, as before.
 func readsFrom(read []inventory.ReadRepository, m link.SourceMoved) bool {
 	for _, r := range read {
-		if r.Own || !sameRepository(r.Repository, m) || (r.Ref != "" && r.Ref != m.Base) {
+		if r.Own || !sameRepository(r.Repository, m) || !followsBase(r.Ref, m.Base) {
 			continue
 		}
 		if len(r.Paths) == 0 || len(m.Paths) == 0 || m.PathsTruncated {
@@ -757,7 +777,7 @@ func unchangedOfMerge(m link.SourceMoved, entries []inventory.Entry,
 // branch, as a context beside its own.
 func packagesSaid(read []inventory.ReadRepository, m link.SourceMoved) bool {
 	for _, r := range read {
-		if !r.Own && sameRepository(r.Repository, m) && (r.Ref == "" || r.Ref == m.Base) && len(r.Paths) > 0 {
+		if !r.Own && sameRepository(r.Repository, m) && followsBase(r.Ref, m.Base) && len(r.Paths) > 0 {
 			return true
 		}
 	}