Fix gemini candidate starvation

backend/services/cse_test.go

@@ -182,6 +182,30 @@ func TestSearchServiceFetchCacheRoundTrip(t *testing.T) {
 	}
 }
 
+func TestSplitSearchDeadlinesReservesEnrichmentWindow(t *testing.T) {
+	deadline := time.Now().Add(20 * time.Second)
+	collectionDeadline, enrichmentDeadline := splitSearchDeadlines(deadline)
+
+	if enrichmentDeadline.IsZero() {
+		t.Fatal("expected enrichment deadline to be preserved")
+	}
+	if !collectionDeadline.Before(enrichmentDeadline) {
+		t.Fatalf("expected collection deadline before enrichment deadline, got %v >= %v", collectionDeadline, enrichmentDeadline)
+	}
+	if gap := enrichmentDeadline.Sub(collectionDeadline); gap < searchEnrichmentReserve-500*time.Millisecond {
+		t.Fatalf("expected reserve close to %v, got %v", searchEnrichmentReserve, gap)
+	}
+}
+
+func TestSplitSearchDeadlinesDoesNotReserveWhenDeadlineIsTooClose(t *testing.T) {
+	deadline := time.Now().Add(2 * time.Second)
+	collectionDeadline, enrichmentDeadline := splitSearchDeadlines(deadline)
+
+	if !collectionDeadline.Equal(enrichmentDeadline) {
+		t.Fatalf("expected identical deadlines when budget is too tight, got %v and %v", collectionDeadline, enrichmentDeadline)
+	}
+}
+
 func TestSearchServiceSkipsArtgridAPIAfter403(t *testing.T) {
 	var apiRequests atomic.Int32
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {