service_down nudges name the service again (V-534)

nudgeValues filled {service} from State.Fact("service_down"), an exact key
mavpoll stopped writing when per-monitor facts landed. The lookup could never
hit, so every variant carrying {service} was rejected as unfillable and the one
nameless variant was the only usable template, every time. A sev4 reaching him
on telegram said only that a service was down.

It now reads loop.DownServices, the same helper the rule fires on, so the
message cannot name a service that is up. Dropped the nameless variant and the
{since} one: service_down facts are keyed by monitor and the rule is
edge-triggered, so neither can fill. service_down joins routine and morning as
a family that always carries a name.

The tests passed through all of this because cand() built the pre-per-monitor
aggregate shape. downCand() builds what a tick actually produces.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011x5DgnExQ5XZy8TZPs5bot

internal/phraser/nudge_templates_test.go

@@ -11,6 +11,63 @@ import (
 	"github.com/kami/maven/internal/store"
 )
 
+// downCand builds a service_down candidate the way a tick actually does it:
+// one fact per kuma monitor under the prefix, carrying the source and value
+// loop.DownServices checks. The old cand() shape wrote a single fact keyed
+// plain "service_down", which mavpoll stopped producing, and that is why the
+// tests passed through the whole of #534.
+func downCand(names ...string) loop.Candidate {
+	now := time.Date(2026, 7, 31, 21, 40, 0, 0, time.UTC)
+	st := loop.State{Now: now, Facts: map[string]store.Fact{}}
+	for _, n := range names {
+		key := loop.ServiceDownPrefix + n
+		st.Facts[key] = store.Fact{
+			Key: key, Ts: now.Add(-3 * time.Minute),
+			Source: loop.ServiceDownSource, Value: `"down"`,
+		}
+	}
+	return loop.Candidate{
+		Rule:     loop.Rule{Name: "service_down", Severity: loop.Sev4},
+		Severity: loop.Sev4, State: st,
+	}
+}
+
+// The nudge he reads on telegram must name what broke. It is a sev4 that
+// reaches him away from the box, so "a service is down" costs him a trip to
+// kuma to learn anything at all.
+func TestNudgeNamesTheDownService(t *testing.T) {
+	// Lowercased before matching: a name that opens the sentence is
+	// capitalized by capitalizeFirst, which is wanted.
+	nt := newTestTemplates(t, 5)
+	for i := 0; i < 40; i++ {
+		body, _ := nt.Nudge(downCand("paperless"))
+		if !strings.Contains(strings.ToLower(body), "paperless") {
+			t.Fatalf("body does not name the service: %q", body)
+		}
+	}
+	// Two down: both named, in the key order the rule itself uses.
+	for i := 0; i < 40; i++ {
+		body, _ := nt.Nudge(downCand("nginx", "paperless"))
+		low := strings.ToLower(body)
+		if !strings.Contains(low, "nginx") || !strings.Contains(low, "paperless") {
+			t.Fatalf("body drops a service: %q", body)
+		}
+	}
+}
+
+// Nothing down means no template fits, and the fallback answers rather than
+// the picker inventing a name.
+func TestNudgeServiceDownWithoutFacts(t *testing.T) {
+	nt := newTestTemplates(t, 5)
+	body, mood := nt.Nudge(downCand())
+	if body != "Сервис не отвечает." {
+		t.Fatalf("fallback body %q", body)
+	}
+	if mood != "neutral" {
+		t.Fatalf("mood %q", mood)
+	}
+}
+
 // cand builds a candidate the way a tick would.
 func cand(rule string, sinceMin int, factKey string) loop.Candidate {
 	now := time.Date(2026, 7, 31, 21, 40, 0, 0, time.UTC)
@@ -46,8 +103,12 @@ func TestNudgeTemplatesLoad(t *testing.T) {
 			t.Errorf("%s: only %d variants", rule, len(set.Variants))
 		}
 		// Every rule needs one variant that needs no value, or a candidate
-		// without context has nothing to say. routine and morning are exempt:
-		// they always carry a name and must always say it.
+		// without context has nothing to say. routine, morning and
+		// service_down are exempt: they always carry a name and must always
+		// say it. service_down's predicate cannot fire without a down fact,
+		// so loop.DownServices always has something to fill {service} with,
+		// and the nameless variant it used to carry was the bug (#534) —
+		// {service} never filled, so that variant was the only fillable one.
 		plain := 0
 		seen := map[string]bool{}
 		for _, v := range set.Variants {
@@ -59,7 +120,7 @@ func TestNudgeTemplatesLoad(t *testing.T) {
 			}
 			seen[v] = true
 		}
-		if plain == 0 && rule != "routine" && rule != "morning" {
+		if plain == 0 && rule != "routine" && rule != "morning" && rule != "service_down" {
 			t.Errorf("%s: every variant needs a placeholder value", rule)
 		}
 	}
@@ -102,8 +163,8 @@ func TestNudgeNoLeftoverPlaceholders(t *testing.T) {
 		cand("water", 0, ""),   // no duration
 		cand("water", 30, ""),  // under an hour
 		cand("water", 200, ""), // hours
-		cand("service_down", 3, "vaultwarden"),
-		cand("service_down", 3, ""), // no service name
+		downCand("vaultwarden"),
+		downCand(), // nothing down: the fallback answers
 		cand("routine:таблетки", 0, ""),
 		cand("morning:утро", 0, ""),
 		cand("unknown_rule", 0, ""),