Set aside a retired seat's consume the trunk catalogue still holds, and say it, so a group that retires a seat passes its check

internal/broker/agreement_catalogue_test.go

@@ -105,7 +105,11 @@ func theCataloguesEvents(t *testing.T) ([]AnEmitter, []AConsumer, []DeclaredSeat
 			emitters = append(emitters, *emitter)
 		}
 		if consumer != nil {
-			consumers = append(consumers, *consumer)
+			kept, setAside := setAsideRetiredSeats(*consumer)
+			for _, note := range setAside {
+				t.Log(note)
+			}
+			consumers = append(consumers, kept)
 		}
 		seats = append(seats, declared...)
 	}
@@ -115,6 +119,53 @@ func theCataloguesEvents(t *testing.T) ([]AnEmitter, []AConsumer, []DeclaredSeat
 	return emitters, consumers, seats
 }
 
+// setAsideRetiredSeats takes out of a consumer the events of a seat the mesh has retired, and says each one.
+// The check judges against the catalogue's trunk (ADR 0484 clause 4), and a group that retires a seat while
+// its catalogue pull request drops the consume (ADR 0524 section 5) meets the trunk still holding it: against
+// that catalogue the seat is gone and the subscription falls back to a module subject nobody owns. It is set
+// aside and logged, never silently dropped; an unknown seat that is not retired is still judged.
+func setAsideRetiredSeats(c AConsumer) (AConsumer, []string) {
+	kept := AConsumer{Module: c.Module}
+	var notes []string
+	for _, want := range c.Consumes {
+		seat, event, named := strings.Cut(want, ".")
+		if replacement, retired := catalogue.RetiredSeats[seat]; named && retired {
+			notes = append(notes, c.Module+" still consumes "+seat+"."+event+"; the seat is retired (its work is "+
+				replacement+"); the catalogue drops it in the same change (ADR 0524 §5), and the check judges against the catalogue's trunk (ADR 0484 clause 4)")
+			continue
+		}
+		kept.Consumes = append(kept.Consumes, want)
+	}
+	return kept, notes
+}
+
+func TestARetiredSeatsConsumeIsSetAsideAndAnUnknownOneIsNot(t *testing.T) {
+	var retired string
+	for name := range catalogue.RetiredSeats {
+		retired = name
+		break
+	}
+	if retired == "" {
+		t.Skip("no seat is retired")
+	}
+	kept, notes := setAsideRetiredSeats(AConsumer{Module: "m",
+		Consumes: []string{retired + ".built", "no-such-seat.built", "plain"}})
+	if len(notes) != 1 || !strings.Contains(notes[0], retired+".built") {
+		t.Fatalf("the retired seat's consume was not set aside and said: %v", notes)
+	}
+	if strings.Join(kept.Consumes, ",") != "no-such-seat.built,plain" {
+		t.Fatalf("what stays to be judged is wrong: %v", kept.Consumes)
+	}
+	if bad := Disagreements([]AnEmitter{{Module: "other", Emits: []string{"x"}}},
+		[]AConsumer{kept}, nil); len(bad) != 0 {
+		t.Fatalf("unexpected: %v", bad)
+	}
+	if bad := Disagreements([]AnEmitter{{Module: "no-such-seat", Emits: []string{"x"}}},
+		[]AConsumer{kept}, nil); len(bad) != 1 {
+		t.Fatalf("an unknown, non-retired consume no longer fails: %v", bad)
+	}
+}
+
 // **Do the derived subjects meet, not just the names?**
 //
 // The check above compares what a consumer asks for against what an emitter says it emits, by name. It