Fail an approval request fast when no subscriber received the prompt

client/internal/approval/broker.go

@@ -90,13 +90,15 @@ var ErrDenied = errors.New("approval denied")
 
 // EventPublisher is the subset of peer.Status used to emit prompts.
 type EventPublisher interface {
+	// PublishEvent reports whether the event reached at least one live
+	// subscriber. A prompt nobody received is one nobody can answer.
 	PublishEvent(
 		severity proto.SystemEvent_Severity,
 		category proto.SystemEvent_Category,
 		msg string,
 		userMsg string,
 		metadata map[string]string,
-	)
+	) bool
 	HasEventSubscribers() bool
 }
 
@@ -171,7 +173,14 @@ func (b *Broker) Request(ctx context.Context, p Prompt) (Decision, error) {
 	if subject == "" {
 		subject = fmt.Sprintf("%s connection requires approval", p.Kind)
 	}
-	b.pub.PublishEvent(proto.SystemEvent_INFO, proto.SystemEvent_APPROVAL, subject, subject, meta)
+	// A subscriber whose queue is full drops the event silently. Waiting out the
+	// timeout for a prompt that never appeared spends the caller's whole
+	// approval window before denying, and tells the user it timed out rather
+	// than that nothing ever asked them.
+	if !b.pub.PublishEvent(proto.SystemEvent_INFO, proto.SystemEvent_APPROVAL, subject, subject, meta) {
+		log.Warnf("approval request %s (%s) reached no subscriber; denying without waiting", id, p.Kind)
+		return zero, ErrNoSubscriber
+	}
 	log.Debugf("approval request %s (%s) emitted: %s", id, p.Kind, subject)
 
 	timer := time.NewTimer(timeout)

client/internal/approval/broker_test.go

@@ -20,6 +20,9 @@ type fakePublisher struct {
 	mu          sync.Mutex
 	subscribers bool
 	events      []*proto.SystemEvent
+	// dropped makes PublishEvent report that no subscriber received the event,
+	// standing in for a subscriber whose queue is full.
+	dropped bool
 }
 
 func (p *fakePublisher) PublishEvent(
@@ -28,7 +31,7 @@ func (p *fakePublisher) PublishEvent(
 	msg string,
 	userMsg string,
 	metadata map[string]string,
-) {
+) bool {
 	p.mu.Lock()
 	p.events = append(p.events, &proto.SystemEvent{
 		Severity:    severity,
@@ -37,7 +40,9 @@ func (p *fakePublisher) PublishEvent(
 		UserMessage: userMsg,
 		Metadata:    metadata,
 	})
+	dropped := p.dropped
 	p.mu.Unlock()
+	return !dropped
 }
 
 func (p *fakePublisher) HasEventSubscribers() bool {
@@ -60,6 +65,25 @@ func (p *fakePublisher) eventCount() int {
 	return len(p.events)
 }
 
+// A subscriber can exist and still not receive the prompt, because its event
+// queue is full and the publisher drops rather than blocks. Waiting out the
+// approval window for a dialog that never opened wastes the caller's whole
+// timeout and then reports it as one, so the broker refuses straight away.
+func TestRequestUndeliveredPromptFailsFast(t *testing.T) {
+	pub := &fakePublisher{subscribers: true, dropped: true}
+	b := New(pub)
+
+	start := time.Now()
+	_, err := b.Request(context.Background(), Prompt{Kind: KindVNC, Subject: "test"})
+	assert.ErrorIs(t, err, ErrNoSubscriber)
+	assert.Less(t, time.Since(start), time.Second, "must not wait out the approval timeout")
+
+	b.mu.Lock()
+	pending := len(b.pending)
+	b.mu.Unlock()
+	assert.Equal(t, 0, pending, "no waiter must be left behind")
+}
+
 // TestRequestNoSubscriberFailsClosed is the core fail-closed invariant:
 // when the UI is not subscribed, the broker must refuse without emitting
 // an event or arming a waiter. A regression here is a silent bypass.