Improve runtime error messages

backend/services/cse.go

@@ -164,7 +164,7 @@ func (s *SearchService) search(query, categories, engine, source string) ([]Sear
 		} `json:"results"`
 	}
 	if err := json.NewDecoder(resp.Body).Decode(&payload); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("searxng JSON decode failed for query %q: %w", query, err)
 	}
 
 	results := make([]SearchResult, 0, len(payload.Results))

backend/services/gemini.go

@@ -65,12 +65,13 @@ Keep the original language when possible. User query: ` + query,
 	endpoint := "https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent?key=" + g.APIKey
 	resp, err := g.Client.Post(endpoint, "application/json", bytes.NewReader(rawBody))
 	if err != nil {
-		return []string{query}, err
+		return []string{query}, fmt.Errorf("gemini query expansion request failed: %w", err)
 	}
 	defer resp.Body.Close()
 
 	if resp.StatusCode >= 300 {
-		return []string{query}, fmt.Errorf("gemini returned status %d for query expansion", resp.StatusCode)
+		data, _ := io.ReadAll(io.LimitReader(resp.Body, 2048))
+		return []string{query}, fmt.Errorf("gemini query expansion returned status %d: %s", resp.StatusCode, strings.TrimSpace(string(data)))
 	}
 
 	var payload struct {
@@ -83,15 +84,15 @@ Keep the original language when possible. User query: ` + query,
 		} `json:"candidates"`
 	}
 	if err := json.NewDecoder(resp.Body).Decode(&payload); err != nil {
-		return []string{query}, err
+		return []string{query}, fmt.Errorf("gemini query expansion response decode failed: %w", err)
 	}
 	if len(payload.Candidates) == 0 || len(payload.Candidates[0].Content.Parts) == 0 {
-		return []string{query}, nil
+		return []string{query}, fmt.Errorf("gemini query expansion returned no candidates")
 	}
 
 	var parsed QueryExpansion
 	if err := json.Unmarshal([]byte(payload.Candidates[0].Content.Parts[0].Text), &parsed); err != nil {
-		return []string{query}, err
+		return []string{query}, fmt.Errorf("gemini query expansion JSON parse failed: %w", err)
 	}
 
 	queries := []string{query}
@@ -159,7 +160,7 @@ Mark only the best matches as recommended=true. Keep reasons concise. Recommend
 
 	if resp.StatusCode >= 300 {
 		data, _ := io.ReadAll(io.LimitReader(resp.Body, 2048))
-		return nil, fmt.Errorf("gemini returned status %d: %s", resp.StatusCode, string(data))
+		return nil, fmt.Errorf("gemini vision returned status %d: %s", resp.StatusCode, strings.TrimSpace(string(data)))
 	}
 
 	var payload struct {
@@ -172,10 +173,10 @@ Mark only the best matches as recommended=true. Keep reasons concise. Recommend
 		} `json:"candidates"`
 	}
 	if err := json.NewDecoder(resp.Body).Decode(&payload); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("gemini vision response decode failed: %w", err)
 	}
 	if len(payload.Candidates) == 0 || len(payload.Candidates[0].Content.Parts) == 0 {
-		return nil, fmt.Errorf("gemini returned no candidates")
+		return nil, fmt.Errorf("gemini vision returned no candidates")
 	}
 
 	var parsed struct {
@@ -186,7 +187,7 @@ Mark only the best matches as recommended=true. Keep reasons concise. Recommend
 		} `json:"recommendations"`
 	}
 	if err := json.Unmarshal([]byte(payload.Candidates[0].Content.Parts[0].Text), &parsed); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("gemini vision JSON parse failed: %w", err)
 	}
 
 	recommendations := make([]AIRecommendation, 0, len(parsed.Recommendations))