fix: 增强价格获取稳定性和日志追踪

问题排查：
1. 缓存命中时验证价格有效性（Price > 0）
2. 外部 API 返回无效价格时拒绝写入缓存
3. 缓存查询层添加详细日志
4. 捕获缓存查询异常并返回 null

改进：
- 缓存价格 <= 0 时忽略缓存重新获取
- 外部 API 价格 <= 0 时抛出异常，避免污染缓存
- 详细日志追踪价格获取全流程

AssetManager.Data/Repositories/MarketDataRepository.cs

@@ -25,9 +25,30 @@ public class MarketDataRepository : IMarketDataRepository
     public async Task<MarketPriceCache?> GetPriceCacheAsync(string symbol, string assetType)
     {
         var cacheKey = GenerateCacheKey(symbol, assetType);
-        return await _db.Queryable<MarketPriceCache>()
-            .Where(p => p.Id == cacheKey && p.ExpiredAt > DateTime.Now)
-            .FirstAsync();
+        _logger.LogDebug("[缓存查询] CacheKey={CacheKey}, Symbol={Symbol}, AssetType={AssetType}", cacheKey, symbol, assetType);
+        
+        try
+        {
+            var result = await _db.Queryable<MarketPriceCache>()
+                .Where(p => p.Id == cacheKey && p.ExpiredAt > DateTime.Now)
+                .FirstAsync();
+            
+            if (result != null)
+            {
+                _logger.LogDebug("[缓存查询成功] CacheKey={CacheKey}, Price={Price}, ExpiredAt={ExpiredAt}", cacheKey, result.Price, result.ExpiredAt);
+            }
+            else
+            {
+                _logger.LogDebug("[缓存查询无结果] CacheKey={CacheKey}", cacheKey);
+            }
+            
+            return result;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "[缓存查询异常] CacheKey={CacheKey}", cacheKey);
+            return null;
+        }
     }
 
     public async Task<bool> SavePriceCacheAsync(MarketPriceCache cache)

AssetManager.Infrastructure/Services/MarketDataService.cs

@@ -48,35 +48,54 @@ public class MarketDataService : IMarketDataService
     public async Task<MarketPriceResponse> GetPriceAsync(string symbol, string assetType)
     {
         var cacheKey = $"{symbol.ToUpper()}_{assetType.ToUpper()}";
-        _logger.LogInformation("获取实时价格: {Symbol}, 资产类型: {AssetType}", symbol, assetType);
-        
-        // 先查缓存
-        var cached = await _marketDataRepo.GetPriceCacheAsync(symbol, assetType);
-        
-        if (cached != null)
-        {
-            _logger.LogDebug("缓存命中: {Symbol} {AssetType}, 价格: {Price}", symbol, assetType, cached.Price);
-            return new MarketPriceResponse
-            {
-                Symbol = cached.Symbol,
-                Price = cached.Price,
-                PreviousClose = cached.PreviousClose ?? 0,
-                Timestamp = cached.FetchedAt,
-                AssetType = cached.AssetType
-            };
-        }
-
-        // 使用 GetOrAdd 模式防止并发重复请求
-        var priceTask = _pendingPriceRequests.GetOrAdd(cacheKey, _ => FetchPriceFromSourceAsync(symbol, assetType));
+        _logger.LogInformation("[价格查询开始] Symbol={Symbol}, AssetType={AssetType}, CacheKey={CacheKey}", symbol, assetType, cacheKey);
         
         try
         {
-            return await priceTask;
+            // 先查缓存
+            var cached = await _marketDataRepo.GetPriceCacheAsync(symbol, assetType);
+            
+            if (cached != null && cached.Price > 0)  // ← 验证价格有效
+            {
+                _logger.LogInformation("[缓存命中] Symbol={Symbol}, Price={Price}, ExpiredAt={ExpiredAt}", symbol, cached.Price, cached.ExpiredAt);
+                return new MarketPriceResponse
+                {
+                    Symbol = cached.Symbol,
+                    Price = cached.Price,
+                    PreviousClose = cached.PreviousClose ?? 0,
+                    Timestamp = cached.FetchedAt,
+                    AssetType = cached.AssetType
+                };
+            }
+
+            if (cached != null && cached.Price <= 0)
+            {
+                _logger.LogWarning("[缓存命中但价格无效] Symbol={Symbol}, Price={Price}，忽略缓存重新获取", symbol, cached.Price);
+            }
+            else
+            {
+                _logger.LogWarning("[缓存未命中] Symbol={Symbol}, AssetType={AssetType}，需要从数据源获取", symbol, assetType);
+            }
+
+            // 使用 GetOrAdd 模式防止并发重复请求
+            var priceTask = _pendingPriceRequests.GetOrAdd(cacheKey, _ => FetchPriceFromSourceAsync(symbol, assetType));
+            
+            try
+            {
+                var result = await priceTask;
+                _logger.LogInformation("[价格获取成功] Symbol={Symbol}, Price={Price}", symbol, result.Price);
+                return result;
+            }
+            finally
+            {
+                // 请求完成后移除（无论成功失败）
+                _pendingPriceRequests.TryRemove(cacheKey, out _);
+            }
         }
-        finally
+        catch (Exception ex)
         {
-            // 请求完成后移除（无论成功失败）
-            _pendingPriceRequests.TryRemove(cacheKey, out _);
+            _logger.LogError(ex, "[价格获取异常] Symbol={Symbol}, AssetType={AssetType}", symbol, assetType);
+            throw;
         }
     }
 
@@ -120,6 +139,13 @@ public class MarketDataService : IMarketDataService
             }
         }
 
+        // 验证价格有效性
+        if (response.Price <= 0)
+        {
+            _logger.LogError("[价格无效] Symbol={Symbol}, Price={Price}, Source={Source}，不写入缓存", symbol, response.Price, source);
+            throw new InvalidOperationException($"获取到的价格无效: {symbol} = {response.Price}");
+        }
+
         // 写入缓存
         await SavePriceCacheAsync(symbol, assetType, response, source);