process: one EventHub pulls the module's one durable consumer, handlers by subject pattern; the views reader registers on it instead of pulling (class fix of B7c finding 1; ADR 0635 §5; issue 1966)

Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i

go/views/process_reader_integration_test.go

@@ -78,3 +78,82 @@ func TestAReaderHearsAnOwnersChangesAsOrdinaryEvents(t *testing.T) {
 		t.Fatalf("other got %s", got)
 	}
 }
+
+// A module has one durable consumer on the shared events stream, so the loops that hear events in one module must share
+// one pull (process.EventHub): two handlers and the views reader on the hub each get their own messages and no other's,
+// and a message nobody takes is acknowledged.
+func TestTheViewsReaderAndTwoHandlersShareTheModulesOneDurable(t *testing.T) {
+	nc, err := nats.Connect(testbus.URL(t))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer nc.Close()
+	js, err := jetstream.New(nc)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	cred := process.Account{Node: "n1", Module: "reader"}
+	kv := viewstest.Serve(t, ctx, js, nc, "o", "modules", "o.o_read_modules", cred.EventConsumerName())
+	hub := process.NewEventHub(t.Logf)
+	got := map[string]chan string{"a": make(chan string, 8), "b": make(chan string, 8)}
+	for name, pattern := range map[string]string{"a": "mesh.mod.p.event.a", "b": "mesh.mod.q.event.b.*"} {
+		if err := hub.Handle(pattern, func(m jetstream.Msg) { _ = m.Ack(); got[name] <- m.Subject() }); err != nil {
+			t.Fatal(err)
+		}
+	}
+	r := &views.ProcessReader{Module: "reader", Hub: hub, Logf: t.Logf,
+		Call: func(tool string, body any) (json.RawMessage, error) {
+			raw, _ := json.Marshal(body)
+			m, err := nc.Request("mesh.mod.o.call.o_read_modules.n0", raw, 5*time.Second)
+			if err != nil {
+				return nil, err
+			}
+			return m.Data, nil
+		}}
+	if _, err := r.Follow("o", "modules", "o.o_read_modules"); err != nil {
+		t.Fatal(err)
+	}
+	r.Start(ctx, js, cred, nil)
+	if err := hub.Start(ctx, js, cred); err != nil {
+		t.Fatal(err)
+	}
+	<-r.Ready()
+	pic, err := r.KeyValue(ctx, "o_modules")
+	if err != nil {
+		t.Fatal(err)
+	}
+	w, err := pic.Watch(ctx, "b")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, s := range []string{"mesh.mod.p.event.a", "mesh.mod.q.event.b.c", "mesh.mod.z.event.nobody", "mesh.mod.p.event.a"} {
+		if _, err := js.Publish(ctx, s, []byte("{}")); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if _, err := kv.Put(ctx, "b", []byte(`{"n":2}`)); err != nil {
+		t.Fatal(err)
+	}
+	for e := range w.Updates() {
+		if e != nil && e.Key() == "b" {
+			break
+		}
+	}
+	for _, want := range []struct{ who, subject string }{{"a", "mesh.mod.p.event.a"}, {"b", "mesh.mod.q.event.b.c"}, {"a", "mesh.mod.p.event.a"}} {
+		if s := <-got[want.who]; s != want.subject {
+			t.Fatalf("handler %s got %s, wanted %s", want.who, s, want.subject)
+		}
+	}
+	if len(got["a"])+len(got["b"]) != 0 {
+		t.Fatal("a handler heard a message that was another's")
+	}
+	cons, err := js.Consumer(ctx, process.EventsStream, cred.EventConsumerName())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if info, err := cons.Info(ctx); err != nil || info.NumAckPending != 0 {
+		t.Fatalf("a message was left unacknowledged: %+v %v", info, err)
+	}
+}