diff --git a/internal/inventory/catalogue.go b/internal/inventory/catalogue.go
index 04218f6..342bb0b 100644
--- a/internal/inventory/catalogue.go
+++ b/internal/inventory/catalogue.go
@@ -78,11 +78,12 @@ func (i *Inventory) RegisterModule(ctx context.Context, m catalogue.Manifest, fr
 	// (novox/hq ADR 0175, to-be 38 WP2.4): a module serving its tools from a container built on the
 	// runtime's image. Refused at registration, by name, for a module that is new to the catalogue
 	// or that was registered in another shape — the mechanism that keeps the old pattern from
-	// returning by habit. **Not refused for a module already registered in that shape**: the
-	// catalogue holds some thirty of them the day the runtime arrives, each moves to a bundle in
-	// its own change (to-be 38 WP4 onward), and a gate that refused every rebuild of every unmoved
-	// module in the meantime would stop the whole pipeline to make a point the record already makes.
-	// Before the runtime exists the pattern is accepted as it always was.
+	// returning by habit. Before the runtime exists the pattern is accepted as it always was.
+	//
+	// *Since 2026-10-04 (to-be 38 WP4b's last step):* refused for **every** module. While some
+	// thirty modules still stood in that shape, one already registered so was rebuilt without
+	// complaint, so the pipeline kept running while each moved; every module has moved since, and
+	// the exception would only let one move back.
 	if m.Module != catalogue.RuntimeModule {
 		if why := catalogue.ToolContainerOnTheRuntime(m, from.Against); why != "" {
 			runtime, err := i.hasModule(ctx, catalogue.RuntimeModule)
@@ -90,13 +91,7 @@ func (i *Inventory) RegisterModule(ctx context.Context, m catalogue.Manifest, fr
 				return err
 			}
 			if runtime {
-				already, err := i.registeredInThatShape(ctx, m.Module)
-				if err != nil {
-					return err
-				}
-				if !already {
-					return fmt.Errorf("%s is not registered: %s", m.Module, why)
-				}
+				return fmt.Errorf("%s is not registered: %s", m.Module, why)
 			}
 		}
 	}
@@ -152,26 +147,6 @@ func (i *Inventory) RegisterModule(ctx context.Context, m catalogue.Manifest, fr
 	return nil
 }
 
-// registeredInThatShape is whether the catalogue already holds this module as a tools container on
-// the runtime's image — judged from the manifest it holds and what that module's newest build stood
-// on, the same two things the gate judges a new registration by. False for a module the catalogue
-// does not hold.
-func (i *Inventory) registeredInThatShape(ctx context.Context, name string) (bool, error) {
-	held, err := i.Catalogue(ctx)
-	if err != nil {
-		return false, err
-	}
-	stored, has := held[name]
-	if !has {
-		return false, nil
-	}
-	against, err := i.BuiltAgainst(ctx)
-	if err != nil {
-		return false, err
-	}
-	return catalogue.ToolContainerOnTheRuntime(stored, against[name]) != "", nil
-}
-
 // hasModule is whether the catalogue holds a module of that name.
 func (i *Inventory) hasModule(ctx context.Context, name string) (bool, error) {
 	var one int
diff --git a/internal/inventory/catalogue_test.go b/internal/inventory/catalogue_test.go
index dbca7af..39f66cc 100644
--- a/internal/inventory/catalogue_test.go
+++ b/internal/inventory/catalogue_test.go
@@ -688,9 +688,9 @@ func TestRegisteringWithoutProvenanceKeepsTheSeat(t *testing.T) {
 
 // Once the node's tool runtime is in the catalogue, a module serving its tools from a container
 // built on the runtime's image is refused at registration, naming the record (novox/hq ADR 0175,
-// to-be 38 WP2.4) — for a module new to the catalogue or one that had moved away from it; a module
-// already standing in that shape is rebuilt as before, so the catalogue's pipeline keeps running
-// while each moves (WP3's amendment). Before the runtime, it is accepted as it always was — so a
+// to-be 38 WP2.4) — for every module, since every module has moved (WP4b's last step; WP3's
+// amendment let one already standing in that shape be rebuilt while each moved). Before the
+// runtime, it is accepted as it always was — so a
 // mesh converts in the order the design says and nothing is refused before there is anything to
 // move to.
 func TestAToolContainerIsRefusedOnceTheRuntimeIsRegistered(t *testing.T) {
@@ -715,11 +715,11 @@ func TestAToolContainerIsRefusedOnceTheRuntimeIsRegistered(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	// **A module already registered in that shape is rebuilt without complaint** (to-be 38 WP2.4 as
-	// amended by WP3): some thirty of them stand the day the runtime arrives, and each moves in its
-	// own change. The gate is against the pattern spreading, not against the pipeline running.
-	if err := inv.RegisterModule(ctx, filter, Source{Repository: "/r", Against: stoodOn}); err != nil {
-		t.Fatalf("a rebuild of a module that already had the pattern was refused: %v", err)
+	// **A module already registered in that shape is refused too** (WP4b's last step): every module
+	// has moved, and a rebuild in the old shape is one moving back.
+	if err := inv.RegisterModule(ctx, filter, Source{Repository: "/r", Against: stoodOn}); err == nil ||
+		!strings.Contains(err.Error(), "ADR 0175") {
+		t.Fatalf("a rebuild of a module in the old pattern was registered beside the runtime: %v", err)
 	}
 	// A module new to the catalogue in that shape is refused, naming the record.
 	newcomer := filter