phraser: name the service that is down (V-444)

Stub and LLM paths both read loop.DownServices, so the message can never name
a service the predicate did not fire on. Two down at once are both named — he
needs the blast radius.

internal/phraser/phraser.go

@@ -142,16 +142,21 @@ func phraseNudge(c loop.Candidate) (body, summary string) {
 		}
 		return body, "take a break"
 	case "service_down":
-		// the fact value is json `"down"`; the key carries the service name.
-		body = "a service on homesrv is down — check journalctl."
-		summary = "service down on homesrv"
-		if f, ok := c.State.Fact("service_down"); ok {
-			if f.Key != "" && f.Key != "service_down" {
-				body = fmt.Sprintf("%s on homesrv is down — check journalctl.", f.Key)
-				summary = fmt.Sprintf("%s down on homesrv", f.Key)
-			}
+		// One fact per kuma monitor, so the nudge names the service. The rule
+		// and this share loop.DownServices, so the message cannot name a
+		// service the predicate did not fire on.
+		down := loop.DownServices(c.State)
+		switch len(down) {
+		case 0:
+			return "a service on homesrv is down — check journalctl.", "service down on homesrv"
+		case 1:
+			return fmt.Sprintf("%s on homesrv is down — check journalctl.", down[0]),
+				fmt.Sprintf("%s down on homesrv", down[0])
+		default:
+			list := strings.Join(down, ", ")
+			return fmt.Sprintf("%s on homesrv are down — check journalctl.", list),
+				fmt.Sprintf("%d services down on homesrv", len(down))
 		}
-		return body, summary
 	default:
 		// generic: name the rule + severity; the LLM impl replaces this with
 		// a prompted phrase. the Stub never editorializes beyond the rule name.