F-tools: the runner's views consumer is proven on the real bus; the heartbeat is asked of the bus only when a bundle wants it, with no race; a seat record says when the bus wrote it; the beat test counts ticks, not sleeps

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

node-tools/internal/bus/bus.go

@@ -1098,6 +1098,17 @@ type Beat struct {
 // the bus's own heartbeat to the loop stopped arriving, the bus ended the loop or no longer answers. A Beat that is
 // not Missed follows the first answer after one that was. A nil beat says nothing.
 func (c *Conn) ConsumeAsBeating(module string, deliver func(Envelope) error, beat func(Beat)) (func(), error) {
+	return c.ConsumeAsBeatingWhen(module, deliver, beat, nil)
+}
+
+// tickHook, when set before a consume starts, is called after each idle heartbeat interval was handled (tests only,
+// through SetTickHook), so a test counts beats instead of sleeping. A consume reads it once, when it starts.
+var tickHook func()
+
+// ConsumeAsBeatingWhen is ConsumeAsBeating that asks the bus about the consumer, and says anything, only while wanted
+// answers true (nil is always): a module whose children asked for no heartbeat costs the bus no consumer-info request.
+func (c *Conn) ConsumeAsBeatingWhen(module string, deliver func(Envelope) error, beat func(Beat), wanted func() bool) (func(), error) {
+	asked := func() bool { return beat != nil && (wanted == nil || wanted()) }
 	durable := ConsumerOf(c.node, module)
 	js, err := jetstream.New(c.nc)
 	if err != nil {
@@ -1106,7 +1117,7 @@ func (c *Conn) ConsumeAsBeating(module string, deliver func(Envelope) error, bea
 	var lastEvent atomic.Int64
 	var missed atomic.Bool
 	say := func(why string) {
-		if beat != nil && missed.CompareAndSwap(false, true) {
+		if asked() && missed.CompareAndSwap(false, true) {
 			beat(Beat{At: time.Now().UTC(), Missed: true, Why: why})
 		}
 	}
@@ -1130,6 +1141,30 @@ func (c *Conn) ConsumeAsBeating(module string, deliver func(Envelope) error, bea
 	h.start()
 	if beat != nil {
 		every := IdleHeartbeat
+		hook := tickHook
+		tickOnce := func() {
+			select {
+			case <-events.Closed():
+				say("the bus ended reading the consumer " + durable)
+				return
+			default:
+			}
+			if !asked() {
+				return
+			}
+			ctx, cancel := context.WithTimeout(context.Background(), every)
+			_, err := js.Consumer(ctx, EventsStream, durable)
+			cancel()
+			if err != nil {
+				say("the bus does not answer about the consumer " + durable + ": " + err.Error())
+				return
+			}
+			if time.Since(time.Unix(0, lastEvent.Load())) < every {
+				return // an event arrived in this interval: it was the word
+			}
+			missed.Store(false)
+			beat(Beat{At: time.Now().UTC()})
+		}
 		go func() {
 			tick := time.NewTicker(every)
 			defer tick.Stop()
@@ -1139,24 +1174,10 @@ func (c *Conn) ConsumeAsBeating(module string, deliver func(Envelope) error, bea
 					return
 				case <-tick.C:
 				}
-				select {
-				case <-events.Closed():
-					say("the bus ended reading the consumer " + durable)
-					continue
-				default:
+				tickOnce()
+				if hook != nil {
+					hook()
 				}
-				ctx, cancel := context.WithTimeout(context.Background(), every)
-				_, err := js.Consumer(ctx, EventsStream, durable)
-				cancel()
-				if err != nil {
-					say("the bus does not answer about the consumer " + durable + ": " + err.Error())
-					continue
-				}
-				if time.Since(time.Unix(0, lastEvent.Load())) < every {
-					continue // an event arrived in this interval: it was the word
-				}
-				missed.Store(false)
-				beat(Beat{At: time.Now().UTC()})
 			}
 		}()
 	}