Add the replay of issue 331, so a tool check refused as no link fails before a merge

Written with only what the node-engine had before its fix, so mesh-lab's prover can
lay it over the commit before (R331).

internal/link/replay331_test.go

@@ -0,0 +1,25 @@
+package link
+
+import (
+	"strings"
+	"testing"
+)
+
+// TestReplay331 is the replay of hq issue 331 (mesh-lab R331), written with only what the node-engine had
+// before its fix so it can be laid over the commit before: every declared tool check on a live machine
+// read "no link to the bus is open" while the link was up, because the link the engine attaches — the NATS
+// link — could not ask a tool, and the queue said that as no link.
+//
+// The NATS link is attached with no connection under it, so no bus is needed: the question must reach the
+// link and fail there, not stop at the queue as if no link were open.
+func TestReplay331(t *testing.T) {
+	q := &Queue{Membership: Membership{Node: "laptop"}}
+	q.attach(t.Context(), &natsLink{node: "laptop"})
+	_, _, err := q.AskTool(t.Context(), "sensors", "sensors_health")
+	if err == nil {
+		t.Fatal("asked on no connection and was answered")
+	}
+	if strings.Contains(err.Error(), "no link to the bus is open") {
+		t.Fatalf("a tool check on the attached NATS link was refused as no link: %v", err)
+	}
+}