feat(web): implement exponential backoff retry pattern in KisApiClient

src/dotnet/QuantEngine.Infrastructure/Services/KisApiClient.cs

@@ -141,6 +141,11 @@ public class KisApiClient : IKisApiClient
         if (!string.IsNullOrEmpty(queryString))
             url += $"?{queryString}";
 
+        int maxAttempts = 3;
+        int delayMs = 1000;
+
+        for (int attempt = 1; attempt <= maxAttempts; attempt++)
+        {
             try
             {
                 var request = new HttpRequestMessage(HttpMethod.Get, url);
@@ -153,13 +158,22 @@ public class KisApiClient : IKisApiClient
                 var result = await response.Content.ReadFromJsonAsync<Dictionary<string, object>>();
                 return result ?? new Dictionary<string, object>();
             }
+            catch (Exception ex) when (attempt < maxAttempts)
+            {
+                _logger.LogWarning(ex, "KIS request failed on attempt {Attempt}/{MaxAttempts}. Retrying in {Delay}ms...", attempt, maxAttempts, delayMs);
+                await Task.Delay(delayMs);
+                delayMs *= 2;
+            }
             catch (Exception ex)
             {
-            _logger.LogError(ex, "KIS request failed: {Path} / {TrId}", path, trId);
-            throw new InvalidOperationException($"KIS read-only request failed for {path} / {trId}.", ex);
+                _logger.LogError(ex, "KIS request failed after {MaxAttempts} attempts: {Path} / {TrId}", maxAttempts, path, trId);
+                throw new InvalidOperationException($"KIS read-only request failed for {path} / {trId} after {maxAttempts} attempts.", ex);
             }
         }
 
+        throw new InvalidOperationException("Unreachable code in KIS client SendRequestAsync");
+    }
+
     private async Task<string> GetOrRefreshTokenAsync(KisCredentials creds)
     {
         var tokenLock = TokenLocks.GetOrAdd(creds.Account, _ => new SemaphoreSlim(1, 1));
@@ -174,6 +188,11 @@ public class KisApiClient : IKisApiClient
 
             var tokenRequest = new { grant_type = "client_credentials", appkey = creds.AppKey, appsecret = creds.AppSecret };
 
+            int maxAttempts = 3;
+            int delayMs = 1000;
+
+            for (int attempt = 1; attempt <= maxAttempts; attempt++)
+            {
                 try
                 {
                     var response = await _httpClient.PostAsJsonAsync(
@@ -201,12 +220,20 @@ public class KisApiClient : IKisApiClient
                     _logger.LogInformation("KIS token refreshed for {Account}; expires at {ExpiresAtUtc}", creds.Account, expiresAt);
                     return accessToken;
                 }
+                catch (Exception ex) when (attempt < maxAttempts)
+                {
+                    _logger.LogWarning(ex, "KIS token refresh failed on attempt {Attempt}/{MaxAttempts}. Retrying in {Delay}ms...", attempt, maxAttempts, delayMs);
+                    await Task.Delay(delayMs);
+                    delayMs *= 2;
+                }
                 catch (Exception ex)
                 {
-                _logger.LogError(ex, "KIS token refresh failed");
-                throw new InvalidOperationException("KIS token refresh failed; check credentials and API availability.", ex);
+                    _logger.LogError(ex, "KIS token refresh failed after {MaxAttempts} attempts", maxAttempts);
+                    throw new InvalidOperationException($"KIS token refresh failed after {maxAttempts} attempts; check credentials and API availability.", ex);
                 }
             }
+            throw new InvalidOperationException("Unreachable code in KIS client TokenRefresh");
+        }
         finally
         {
             tokenLock.Release();