Refactor search fallback and preview flows

backend/services/gemini.go

@@ -164,16 +164,21 @@ User query: ` + query,
 	}
 
 	maxImages := min(len(candidates), 10)
+	visualCount := 0
 	for idx := 0; idx < maxImages; idx++ {
 		img, mimeType, err := fetchCandidateVisualInlineData(g.Client, candidates[idx])
 		if err != nil {
 			continue
 		}
+		visualCount++
 		parts = append(parts,
 			geminiPart{"text": fmt.Sprintf("Candidate %d: title=%s source=%s link=%s", idx, candidates[idx].Title, candidates[idx].Source, candidates[idx].Link)},
 			geminiPart{"inlineData": map[string]string{"mimeType": mimeType, "data": img}},
 		)
 	}
+	if visualCount == 0 {
+		return nil, fmt.Errorf("no candidate thumbnails or preview frames could be fetched for gemini vision")
+	}
 
 	body := map[string]any{
 		"contents": []map[string]any{
@@ -248,18 +253,7 @@ User query: ` + query,
 	}
 
 	if len(recommendations) == 0 {
-		for _, candidate := range candidates[:min(8, len(candidates))] {
-			recommendations = append(recommendations, AIRecommendation{
-				Title:           candidate.Title,
-				Link:            candidate.Link,
-				Snippet:         candidate.Snippet,
-				ThumbnailURL:    candidate.ThumbnailURL,
-				PreviewVideoURL: candidate.PreviewVideoURL,
-				Source:          candidate.Source,
-				Reason:          "Gemini Vision 평가를 받지 못해 키워드 기준으로 보강된 결과입니다.",
-				Recommended:     false,
-			})
-		}
+		recommendations = BuildFallbackRecommendations(candidates, 8, "Gemini Vision 평가를 받지 못해 키워드 기준으로 보강된 결과입니다.")
 	}
 
 	return recommendations, nil