Compose each machine in the merge gate with its engine's contract, so moved modules are handed there as on the mesh (issue 969)

cmd/mesh-controller/merge_gate_handing_test.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"testing"
+	"time"
+
+	snapshot "github.com/novox/mesh-controller/internal/facts"
+	"github.com/novox/mesh-controller/internal/link"
+)
+
+// Issue 969: the gate composes a machine as the mesh does, so a moved module is handed where the machine takes
+// handed files and composed the old way where it does not.
+func TestIssue969TheGateGivesAMachineItsContractSoItTakesHandedFiles(t *testing.T) {
+	taken := time.Date(2026, 10, 16, 12, 0, 0, 0, time.UTC)
+
+	stated, ok := standInHealth(snapshot.Machine{Name: "f35", Contract: link.HandedContract}, taken)
+	if !ok || !takesHanded(stated, ok) {
+		t.Fatalf("a machine whose engine takes handed files must be given that in the gate: %+v, %v", stated, ok)
+	}
+	old, ok := standInHealth(snapshot.Machine{Name: "e12", Contract: link.HandedContract - 1}, taken)
+	if !ok || takesHanded(old, ok) {
+		t.Fatalf("a machine whose engine is older must not take handed files: %+v, %v", old, ok)
+	}
+	none, ok := standInHealth(snapshot.Machine{Name: "d01"}, taken)
+	if ok || takesHanded(none, ok) {
+		t.Fatalf("a snapshot that carries no contract states nothing: %+v, %v", none, ok)
+	}
+}