each agenda grammar is tested against its own example (V-552)

Replaces a test whose name promised more than its body checked: it
looped the grammars asserting Pattern != nil, which regexp.MustCompile
already guarantees at init. Asserting the grammars pass IsAgendaQuestion
would be true by construction, since the first arm is that same loop.

A hand-written example per grammar name catches what neither does: a
grammar edited until it no longer matches the case its comment gives,
and a new grammar nobody wrote an example for.

internal/router/agendaq_test.go

@@ -39,3 +39,28 @@ func TestIsAgendaQuestionSeparatesHisDayFromTheWorld(t *testing.T) {
 		}
 	}
 }
+
+// One hand-written utterance per agenda grammar, keyed by name. Asserting that
+// the grammars pass IsAgendaQuestion would be true by construction, since the
+// first arm is the loop over them. This asserts something else: that each
+// grammar still matches the case its own comment gives, and that the set of
+// grammars has not grown a member nobody wrote an example for.
+func TestEachAgendaGrammarStillMatchesItsOwnExample(t *testing.T) {
+	examples := map[string]string{
+		"calendar-query":    "что в календаре на завтра",
+		"agenda-query":      "что у меня сегодня",
+		"plan-day-query":    "какие планы на завтра",
+		"rest-of-day-query": "что дальше?",
+		"event-time-query":  "когда планёрка",
+	}
+	for _, g := range AgendaQueryGrammars() {
+		u, ok := examples[g.Name]
+		if !ok {
+			t.Errorf("agenda grammar %q has no example here — add one", g.Name)
+			continue
+		}
+		if !g.Pattern.MatchString(u) {
+			t.Errorf("grammar %q no longer matches %q", g.Name, u)
+		}
+	}
+}