diff --git a/modules/mesh-delivery-indexer/internal/index/branch_take_in.go b/modules/mesh-delivery-indexer/internal/index/branch_take_in.go
index 0f274de0..b1df57d8 100644
--- a/modules/mesh-delivery-indexer/internal/index/branch_take_in.go
+++ b/modules/mesh-delivery-indexer/internal/index/branch_take_in.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"maps"
+	"strings"
 
 	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-contracts/go/seats/meshdelivery"
 	"git.novox.be/novox/mesh-sdk/go/process"
@@ -51,5 +52,10 @@ func (ix *Indexer) ApplyBranchSource(ctx context.Context, branch string, a meshd
 	if err != nil {
 		return err
 	}
+	// A cycle with a build edge no running version breaks is refused here as at the trunk's take-in (design 47 G §49, A-326).
+	if cycle := RefusedCycle(WithEdges(ix.withActs(ctx, entries))); cycle != nil {
+		ix.logf("catalog graph: the branch %s at source revision %d keeps no revision: its catalog graph holds a cycle with a build edge, which no running version breaks (design 47 G §49): %s; taken in again at its next source-moved", branch, a.Revision, strings.Join(cycle, ", "))
+		return nil
+	}
 	return ix.KeepBranchEntries(ctx, branch, a.Revision, entries)
 }
diff --git a/modules/mesh-delivery-indexer/internal/index/branch_take_in_test.go b/modules/mesh-delivery-indexer/internal/index/branch_take_in_test.go
index 253245a2..64786d5b 100644
--- a/modules/mesh-delivery-indexer/internal/index/branch_take_in_test.go
+++ b/modules/mesh-delivery-indexer/internal/index/branch_take_in_test.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"maps"
 	"slices"
+	"strings"
 	"testing"
 
 	"git.novox.be/novox/mesh-delivery/modules/mesh-delivery-contracts/go/seats/meshcatalog"
@@ -73,3 +74,40 @@ func TestABranchOtherThanTheFirstIsTakenInIntoItsOwnRevisionAndTheTrunkIsLeftAlo
 		t.Errorf("the same heads said %d revisions (%v), want one", len(said), err)
 	}
 }
+
+// Design 47 G §49, A-326: a branch take-in refuses a cycle with a build edge as the trunk's does: the branch keeps no revision
+// at those heads and says why, naming every artifact on the cycle.
+func TestABranchTakeInKeepsNoRevisionWithARefusedCycle(t *testing.T) {
+	ctx := context.Background()
+	mods := builderModules(t)
+	for i, m := range mods {
+		switch m.name {
+		case "avahi": // avahi is built on mesh-tools (kind 3) ...
+			mods[i].manifest = strings.Replace(catalogueManifest(t, "avahi"), `"build": {`, `"build": {
+    "on": [{"arg": "RUNTIME_BASE", "module": "mesh-tools", "artifact": "tools"}],`, 1)
+		case "mesh-tools": // ... and mesh-tools' artifact needs avahi's (kind 2): no build seat breaks the cycle.
+			mods[i].manifest = strings.Replace(m.manifest, `"name": "tools",`, `"name": "tools", "needs": ["avahi:tools"],`, 1)
+		}
+	}
+	ix, _, merged := newFormIndexerUnmerged(t, mods...)
+	ix.Revisions = newMemObjects(0)
+	ix.Graph = newMem()
+	var logs strings.Builder
+	ix.Logf = func(format string, args ...any) { fmt.Fprintf(&logs, format+"\n", args...) }
+	ix.Message = func(context.Context, string, string, int) ([]byte, error) { return json.Marshal(merged) }
+	var said []meshcatalog.CatalogRevisionEvent
+	ix.SayCatalogRevision = func(_ context.Context, e meshcatalog.CatalogRevisionEvent) error {
+		said = append(said, e)
+		return nil
+	}
+	answer := meshdelivery.SourceAnswer{Branch: "beta", Revision: 9, Repositories: []meshdelivery.SourceHead{{Repository: catalogueRepo, Head: merged.Merge, Trunk: "beta"}}}
+	if err := ix.ApplyBranchSource(ctx, "beta", answer); err != nil {
+		t.Fatal(err)
+	}
+	if _, _, err := ReadRevision(ctx, ix.Revisions, BranchObject("beta", 1)); err == nil || len(said) != 0 {
+		t.Errorf("the branch kept a revision with a refused cycle (said %+v)", said)
+	}
+	if want := "mesh-tools:tools, avahi:tools, mesh-tools:tools"; !strings.Contains(logs.String(), want) {
+		t.Errorf("the journal %q does not say the cycle %s", logs.String(), want)
+	}
+}