router: a reminder with no subject asks instead of guessing (V-383)

Slots.Text was the raw utterance for every intent, so a reminder could not
have an empty subject. StillMissing never reported SlotText, the question
"О чём напомнить?" was unaskable, and the branch in PendingQuestion.Answer
that fills a text slot could only overwrite the whole request.

The LLM path now keeps the model's own text, empty included, and the gate
turns a subjectless reminder into a question. The classifier path is
unchanged: it has no subject parser, so the utterance is the only signal it
has.

internal/router/llmrouter_test.go

@@ -356,3 +356,35 @@ func TestRouterLLMFactWithResolvedKeyStaysConfident(t *testing.T) {
 		t.Fatalf("a fact the parser could key must not clarify: %+v", d)
 	}
 }
+
+// A reminder with a time and no subject must come back empty and gated, not
+// backfilled with the raw words. "напомни в 11" carries an hour and nothing to
+// say at that hour; parking the utterance in Text made the request look
+// complete, so the daemon set a reminder that fires saying "напомни в 11"
+// (Vikunja #383).
+func TestLLMReminderWithoutSubjectAsksInsteadOfGuessing(t *testing.T) {
+	r := newLLMTestRouter(t, `{"intent":"reminder"}`)
+	d, err := r.Route(context.Background(), "напомни в 11", refNow())
+	if err != nil {
+		t.Fatalf("route: %v", err)
+	}
+	if d.Slots.Text != "" {
+		t.Fatalf("subject backfilled from the utterance: %q", d.Slots.Text)
+	}
+	if !d.Clarify {
+		t.Fatalf("a subjectless reminder was accepted, confidence %v", d.Confidence)
+	}
+}
+
+// The gate is about the subject, not about reminders in general: one that has
+// both halves still runs without a question.
+func TestLLMReminderWithSubjectIsNotGated(t *testing.T) {
+	r := newLLMTestRouter(t, `{"intent":"reminder","text":"позвонить маме"}`)
+	d, err := r.Route(context.Background(), "напомни в 11 позвонить маме", refNow())
+	if err != nil {
+		t.Fatalf("route: %v", err)
+	}
+	if d.Clarify {
+		t.Fatalf("a complete reminder was sent back as a question: %+v", d.Slots)
+	}
+}