fix: VLM识别修复 - 去System Message + 低温 + 精简提示词

backend/src/Health.WebApi/Endpoints/ai_chat_endpoints.cs

@@ -266,24 +266,26 @@ public static class AiChatEndpoints
                     await file.CopyToAsync(stream, ct);
 
                 var compressedPath = Path.Combine(uploadsDir, $"compressed_{safeName}");
-                CompressImage(filePath, compressedPath, maxWidth: 1280, quality: 85L);
+                CompressImage(filePath, compressedPath, maxWidth: 1024, quality: 90L);
                 var compressedBytes = await File.ReadAllBytesAsync(compressedPath, ct);
                 var base64 = Convert.ToBase64String(compressedBytes);
                 imageUrls.Add($"data:image/jpeg;base64,{base64}");
             }
 
             var prompt = """
-    Describe everything you see in this image in detail. What objects are present? What are their colors, shapes, labels?
-    If there are any food items, drinks, or beverages, identify them specifically by name.
-    Then, for each food/drink item, estimate the portion size and calories (kcal).
-    Return ONLY a JSON array: [{"name":"item name","portion":"estimated portion","calories":estimated_calories}]
-    If you cannot identify something, say so in the name field.
+    识别这张图片中最主要的食物或饮品（最多2个）。只返回JSON数组，格式：
+    [{"name":"名称","portion":"份量","calories":热量}]
+    不要说图片里没有的东西。不要编造。
     """;
 
             try
             {
                 var response = await visionClient.VisionAsync(prompt, imageUrls, userText: "请看图识别食物", maxTokens: 8192, ct: ct);
                 var result = response.Choices?.FirstOrDefault()?.Message?.Content ?? "{}";
+                // 记录VLM原始返回用于排查
+                var uploadsDir2 = Path.Combine(Directory.GetCurrentDirectory(), "uploads");
+                var logPath = Path.Combine(uploadsDir2, $"vlm_log_{DateTime.Now:HHmmss}.txt");
+                await File.WriteAllTextAsync(logPath, $"MODEL: {Environment.GetEnvironmentVariable("VLM_MODEL")}\nIMAGE_SIZE: {imageUrls.FirstOrDefault()?.Length ?? 0}\nRESPONSE:\n{result}", ct);
                 return Results.Ok(new { code = 0, data = result, message = (string?)null });
             }
             catch (Exception ex)