diff --git a/cmd/mesh-controller/main.go b/cmd/mesh-controller/main.go
index e3e346f7..e56bcac1 100644
--- a/cmd/mesh-controller/main.go
+++ b/cmd/mesh-controller/main.go
@@ -73,6 +73,8 @@ func run() error {
 	}
 
 	switch args[0] {
+	case "register":
+		return registerCommand(ctx, args[1:])
 	case "build", "rebuild":
 		// **The hand build goes with the asks** (novox/hq ADR 0501 §5): refused by name, naming the replacement.
 		return removedByName(args[0])
diff --git a/cmd/mesh-controller/register.go b/cmd/mesh-controller/register.go
new file mode 100644
index 00000000..1c7a727b
--- /dev/null
+++ b/cmd/mesh-controller/register.go
@@ -0,0 +1,76 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+
+	sdkdelivery "git.novox.be/novox/mesh-sdk/go/delivery"
+	"github.com/novox/mesh-controller/internal/builderkeys"
+)
+
+// The terminal's exception becomes a registration, not a build (novox/hq ADR 0501 §4; issue 1851, A11b).
+//
+// `register <module> <owner>/<repository> <path>`, at the controller's terminal alone: the operator names the module,
+// its repository and its path, and the controller registers it from the builder's done key of the fingerprint the
+// indexer's trunk value of that module names — the registration a build asked at the terminal used to make for a
+// repository the catalogue does not build (ADR 0432 §3, ADR 0420 §7). No verb reaches it (terminalOnlyCommands), and it
+// asks no build: a key not done is waited for, and said.
+func registerCommand(ctx context.Context, args []string) error {
+	if len(args) != 3 {
+		return errors.New("register <module> <owner>/<repository> <path>  (the path \".\" for a module at the repository's root)")
+	}
+	if !startedAtTheTerminal() {
+		return terminalRefusal("register is run at the controller's terminal only, never through a verb: it registers " +
+			"a module from a repository the catalogue does not build, and whoever may call a verb includes agents " +
+			"(novox/hq ADR 0266, ADR 0501 §4). Nothing was done")
+	}
+	module, repository, path := args[0], strings.Trim(args[1], "/"), strings.Trim(args[2], "/")
+	if path == sdkdelivery.RootPath {
+		path = ""
+	}
+	open, err := openStores(ctx)
+	if err != nil {
+		return err
+	}
+	defer open.Close()
+	keys, closeKeys, err := openBuilderKeys()
+	if err != nil {
+		return err
+	}
+	defer closeKeys()
+	trunk, err := keys.ModuleAt(ctx, module, "")
+	if errors.Is(err, builderkeys.ErrNoValue) {
+		return fmt.Errorf("the indexer holds no trunk value of %s: a module is registered from the builder's key of a "+
+			"merged trunk, and %s has none yet. Nothing was registered", module, module)
+	}
+	if err != nil {
+		return err
+	}
+	if err := sameModuleSource(module, repository, path, trunk); err != nil {
+		return err
+	}
+	manifest, kept, err := takeInKey(ctx, open.inventory, keys, keyTake{Module: module, Trunk: trunk,
+		Ask: registrationAsk{Terminal: true}})
+	if errors.Is(err, errKeyWaits) {
+		return fmt.Errorf("%s is not registered yet, and nothing was asked: %v. Run register again once its key is done",
+			module, err)
+	}
+	if err != nil {
+		return err
+	}
+	fmt.Printf("%s %s registered from the builder's key %s (%s at %.8s), as asked at the controller's terminal; "+
+		"assigned nowhere\n", manifest.Module, manifest.Version, short(kept.SourceFingerprint), repository, kept.Commit)
+	return nil
+}
+
+// sameModuleSource refuses a registration whose repository or path is not the one the indexer's trunk value names: the
+// operator names exactly what is registered (ADR 0501 §4).
+func sameModuleSource(module, repository, path string, trunk sdkdelivery.Module) error {
+	if !strings.EqualFold(trunk.Repository, repository) || keyPath(trunk) != path {
+		return fmt.Errorf("the indexer holds %s in %s at %q, not in %s at %q: the registration names exactly what it "+
+			"registers. Nothing was registered", module, trunk.Repository, orRoot(keyPath(trunk)), repository, orRoot(path))
+	}
+	return nil
+}
diff --git a/cmd/mesh-controller/register_test.go b/cmd/mesh-controller/register_test.go
new file mode 100644
index 00000000..99b1e45f
--- /dev/null
+++ b/cmd/mesh-controller/register_test.go
@@ -0,0 +1,38 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+
+	sdkdelivery "git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// A11b (ADR 0501 §4): the terminal's registration names exactly the module's repository and path the indexer holds,
+// and no verb reaches it.
+func TestTheTerminalsRegistrationNamesItsSourceExactlyAndNoVerbReachesIt(t *testing.T) {
+	trunk := sdkdelivery.Module{Repository: "someone/app", Path: sdkdelivery.RootPath, Commit: "c0ffee"}
+	if err := sameModuleSource("app", "someone/app", "", trunk); err != nil {
+		t.Fatalf("the source the indexer holds is refused: %v", err)
+	}
+	if err := sameModuleSource("app", "someone/other", "", trunk); err == nil || !strings.Contains(err.Error(), "someone/app") {
+		t.Fatalf("another repository is taken: %v", err)
+	}
+	if err := sameModuleSource("app", "someone/app", "modules/app", trunk); err == nil {
+		t.Fatal("another path is taken")
+	}
+	// The generic verb only reads; and register is the terminal's only, whatever reads.
+	if _, err := argvFor("command", map[string]any{"command": "register app someone/app ."}); err == nil {
+		t.Fatal("a verb reaches the terminal's registration")
+	}
+	var refused *heldAtTheTerminal
+	if err := terminalOnly([]string{"register", "app", "someone/app", "."}); !errors.As(err, &refused) {
+		t.Fatalf("register is not the terminal's only: %v", err)
+	}
+	t.Setenv(verbVar, "command")
+	var held *heldAtTheTerminal
+	if err := registerCommand(context.Background(), []string{"app", "someone/app", "."}); !errors.As(err, &held) {
+		t.Fatalf("register through a verb: %v", err)
+	}
+}
diff --git a/cmd/mesh-controller/seatverbs.go b/cmd/mesh-controller/seatverbs.go
index c07fe9ba..46485477 100644
--- a/cmd/mesh-controller/seatverbs.go
+++ b/cmd/mesh-controller/seatverbs.go
@@ -1784,6 +1784,9 @@ var terminalOnlyCommands = map[string]string{
 	"broker":   "the bus's accounts",
 	"api":      "the controller's API keys",
 	"licence":  "the licences' secrets",
+	// The terminal's exception of ADR 0501 §4: a module from a repository the catalogue does not build, registered
+	// from its done key.
+	"register": "a module's registration from a repository the catalogue does not build",
 }
 
 // givenAtTheDesk is exactly the line the `give` and `secret-ask` verbs compose, and nothing beside it: `secret ask