fix(external-system-gateway): resolve ExternalSystemGateway-004..010 — honour retry settings, dispose HTTP messages, fix URL building, truncate error bodies, fix connection leak

src/ScadaLink.ExternalSystemGateway/DatabaseGateway.cs

@@ -45,11 +45,29 @@ public class DatabaseGateway : IDatabaseGateway
             throw new InvalidOperationException($"Database connection '{connectionName}' not found");
         }
 
-        var connection = new SqlConnection(definition.ConnectionString);
-        await connection.OpenAsync(cancellationToken);
+        var connection = CreateConnection(definition.ConnectionString);
+        try
+        {
+            await connection.OpenAsync(cancellationToken);
+        }
+        catch
+        {
+            // OpenAsync failed (unreachable server, bad credentials, cancellation) —
+            // dispose the just-created connection before the exception propagates so
+            // it is not leaked (ExternalSystemGateway-010).
+            await connection.DisposeAsync();
+            throw;
+        }
         return connection;
     }
 
+    /// <summary>
+    /// Creates the underlying ADO.NET connection for a connection string. Virtual so
+    /// tests can substitute a connection whose <c>OpenAsync</c> fails.
+    /// </summary>
+    internal virtual DbConnection CreateConnection(string connectionString) =>
+        new SqlConnection(connectionString);
+
     /// <summary>
     /// Submits a SQL write to the store-and-forward engine for reliable delivery.
     /// </summary>
@@ -78,12 +96,15 @@ public class DatabaseGateway : IDatabaseGateway
             Parameters = parameters
         });
 
+        // The per-connection retry settings are passed through verbatim — a
+        // configured MaxRetries of 0 means "never retry" and must NOT be
+        // collapsed to the S&F default (ExternalSystemGateway-004).
         await _storeAndForward.EnqueueAsync(
             StoreAndForwardCategory.CachedDbWrite,
             connectionName,
             payload,
             originInstanceName,
-            definition.MaxRetries > 0 ? definition.MaxRetries : null,
+            definition.MaxRetries,
             definition.RetryDelay > TimeSpan.Zero ? definition.RetryDelay : null);
     }