DLV-F3r sdk: a reader hears a views event by its data, and a gap is asked as a gap (A7's request)

views.HearEvent routes one event given as its data, for the tool runner, which takes the owners' events by its own
path; Follower.Gap asks once more without counting it by hand. Hear is HearEvent on a consumer's message.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

go/views/follow.go

@@ -317,31 +317,41 @@ func (f *Follower) Apply(ev Event) (gap bool, why string) {
 // that follower's first view once more on its own goroutine, said in the log. A message it cannot read is terminated.
 func Hear(ctx context.Context, followers map[string]*Follower, logf func(string, ...any)) func(jetstream.Msg) {
 	return func(m jetstream.Msg) {
-		ev, err := DecodeEvent(m.Data())
-		if err != nil {
+		if err := HearEvent(ctx, followers, m.Data(), logf); err != nil {
 			logf("views: %s is not a views event, dropped: %v", m.Subject(), err)
 			_ = m.Term()
 			return
 		}
-		f := followers[ev.State]
-		if f == nil {
-			_ = m.Ack() // a state this reader does not follow
-			return
-		}
-		if gap, why := f.Apply(ev); gap {
-			logf("views: a gap in %s (%s): its first view %s is asked once more", ev.State, why, f.Tool)
-			go func() {
-				f.mu.Lock()
-				f.init()
-				f.st.Why = "a gap: " + why
-				f.mu.Unlock()
-				_ = f.askUntil(ctx, "a gap: "+why, false)
-			}()
-		}
 		_ = m.Ack()
 	}
 }
 
+// HearEvent is Hear for one event given as its data, for a reader that takes the owner's events by another path than
+// a consumer of its own (the tool runner's): routed to the follower of its state, an event of a state it does not
+// follow passed over, and a gap asked once more on its own goroutine as a gap, never as a hand ask (Gap). Data that is
+// not a views event is answered as an error, and nothing is asked.
+func HearEvent(ctx context.Context, followers map[string]*Follower, data []byte, logf func(string, ...any)) error {
+	ev, err := DecodeEvent(data)
+	if err != nil {
+		return err
+	}
+	f := followers[ev.State]
+	if f == nil {
+		return nil // a state this reader does not follow
+	}
+	if gap, why := f.Apply(ev); gap {
+		logf("views: a gap in %s (%s): its first view %s is asked once more", ev.State, why, f.Tool)
+		go func() { _ = f.Gap(ctx, why) }()
+	}
+	return nil
+}
+
+// Gap asks the first view once more for a gap the reader saw, until answered or ctx ends: counted among its asks,
+// never among its asks by hand.
+func (f *Follower) Gap(ctx context.Context, why string) error {
+	return f.askUntil(ctx, "a gap: "+why, false)
+}
+
 // AskVia is a Follower's Ask through a process's call of the owner's tool (process.Conn.Call), decoding its answer.
 func AskVia(call func(key string, body any) (json.RawMessage, error), tool string) func(context.Context, string) (Answer, error) {
 	return func(_ context.Context, after string) (Answer, error) {

go/views/views_test.go

@@ -188,6 +188,30 @@ func TestViews(t *testing.T) {
 			t.Errorf("d = %s, %v at %d", v, ok, f.Status().Revision)
 		}
 	})
+	t.Run("an event heard by its data asks a gap once more as a gap, never by hand", func(t *testing.T) {
+		asked := make(chan struct{}, 4)
+		f, _ := follower(func(ctx context.Context, after string) (Answer, error) {
+			asked <- struct{}{}
+			return answer(ctx, after)
+		})
+		_ = f.Start(context.Background())
+		<-asked
+		raw, _ := ev(12, "a", `{}`).Encode()
+		if err := HearEvent(context.Background(), map[string]*Follower{"modules": f}, raw, t.Logf); err != nil {
+			t.Fatal(err)
+		}
+		select {
+		case <-asked:
+		case <-time.After(3 * time.Second):
+			t.Fatal("a gap heard by its data asked nothing")
+		}
+		if s := f.Status(); s.Asks != 2 || s.ByHand != 0 {
+			t.Errorf("a gap was counted by hand: %+v", s)
+		}
+		if err := HearEvent(context.Background(), nil, []byte("not an event"), t.Logf); err == nil {
+			t.Error("data that is no views event was taken")
+		}
+	})
 	t.Run("an event names its state on its subject, and decodes as it was encoded", func(t *testing.T) {
 		if s := StateOfEvent("mesh.stream.mesh-delivery-indexer.event.views.config-candidates"); s != "config-candidates" {
 			t.Errorf("state of subject = %q", s)