Count a dead letter by when it was kept, so one kept late still counts (issue 440)

The give-up time is not newer for every letter kept: a notice that could
not be kept is offered again a minute later, so a later give-up can be kept
first and the one after it read as not fresh. The stored time rises with the
stream's sequence. A consumer whose letters vanish between the two reads is
left out of the look instead of counted as a look, and the skip of a
token-less max-deliveries advisory now has a test of its own.

cmd/mesh-controller/advisories_counted_test.go

@@ -166,3 +166,15 @@ func TestAMessageThatCouldNotBeKeptIsStillSaidFromTheAdvisory(t *testing.T) {
 		t.Fatalf("%+v", said)
 	}
 }
+
+// A max-deliveries advisory without a token names a consumer's dead-letter key, which only DEAD_LETTERS
+// says (novox/hq issues 330 and 440): with nothing held, the advisory alone raises nothing.
+func TestAMaxDeliveriesAdvisoryAloneRaisesNothing(t *testing.T) {
+	at := time.Date(2026, 10, 10, 21, 4, 0, 0, time.UTC)
+	f := &signalFacts{now: at, host: "novox", advisories: []link.Advisory{{Kind: link.AdvisoryMaxDeliveries,
+		ID: "EVENTS.media_sonarr", Stream: "EVENTS", Consumer: "media_sonarr",
+		Said: "sonarr on media handed message 7 over 5 times and gave up on it", First: at, Last: at, Count: 1}}}
+	if said := watchAdvisories(f); len(said) != 0 {
+		t.Fatalf("said %+v", said)
+	}
+}

cmd/mesh-controller/signals.go

@@ -576,9 +576,11 @@ func watchDeadLetters(f *signalFacts) []conditions.Observation {
 			messages, them = fmt.Sprintf("%d messages", n), "them"
 		}
 		who := consumerWho(stream, consumer)
-		// DEAD_LETTERS is a record of what was given up on: the condition counts the messages and says when
-		// the newest was given up, never how often the controller looked (novox/hq issues 402 and 440).
-		// Without that time it counts its looks, as a source of the present does.
+		// DEAD_LETTERS is a record of what was given up on: the condition says when the newest held message
+		// was kept, and its count is a running total of the messages given up on while it is open, never
+		// how often the controller looked (novox/hq issues 402 and 440). It is at least the number held now,
+		// and does not go down when one is delivered again or dropped. Without that time it counts its
+		// looks, as a source of the present does.
 		happened, times := f.deadLettersNewest[key], 0
 		if !happened.IsZero() {
 			times = n

cmd/mesh-controller/watchdogs.go

@@ -80,8 +80,8 @@ type signalFacts struct {
 	// deadLetters are how many messages DEAD_LETTERS holds per consumer, by `<stream>.<consumer>`
 	// (novox/hq issue 330): each consumer's max-deliveries condition is open while it holds any.
 	deadLetters map[string]int
-	// deadLettersNewest is when each of those consumers last gave up on a message DEAD_LETTERS still
-	// holds: the condition counts the messages given up on, not the looks (novox/hq issue 440).
+	// deadLettersNewest is when DEAD_LETTERS kept the newest message it holds for each of those
+	// consumers: the condition counts the messages given up on, not the looks (novox/hq issue 440).
 	deadLettersNewest map[string]time.Time
 	advisoriesErr     error
 
@@ -355,6 +355,13 @@ func (w *watchdogs) gather(ctx context.Context) *signalFacts {
 	}
 	if f.advisoriesErr == nil && len(f.deadLetters) > 0 {
 		f.deadLettersNewest, f.advisoriesErr = link.NewestDeadLetters(w.js.Context(), f.deadLetters)
+		for key := range f.deadLetters {
+			if _, ok := f.deadLettersNewest[key]; !ok && f.advisoriesErr == nil {
+				// Delivered again or dropped between the two reads: left out of this look, rather than
+				// observed without a time and counted as a look (novox/hq issue 440).
+				delete(f.deadLetters, key)
+			}
+		}
 	}
 	f.handActs, f.handActsErr = w.gatherHandActs(ctx, now)
 	f.facts.taken, _, f.facts.began, f.facts.err = exportedFacts.last()