add xmldoc comments

web/backend/Infrastructure/Infrastructure.Repository/Sql/DefaultSqlConnectionFactory.cs

@@ -4,6 +4,11 @@ using Microsoft.Extensions.Configuration;
 
 namespace Infrastructure.Repository.Sql;
 
+/// <summary>
+/// Default <see cref="ISqlConnectionFactory"/> implementation that creates SQL Server connections,
+/// resolving the connection string from environment variables or application configuration.
+/// </summary>
+/// <param name="configuration">The application configuration, used as a fallback source for the connection string.</param>
 public class DefaultSqlConnectionFactory(IConfiguration configuration)
     : ISqlConnectionFactory
 {
@@ -11,6 +16,17 @@ public class DefaultSqlConnectionFactory(IConfiguration configuration)
         configuration
     );
 
+    /// <summary>
+    /// Resolves the SQL Server connection string, preferring (in order): the <c>DB_CONNECTION_STRING</c>
+    /// environment variable, a connection string built from individual <c>DB_*</c> environment variables
+    /// via <see cref="SqlConnectionStringHelper.BuildConnectionString"/>, and finally the <c>"Default"</c>
+    /// connection string from <paramref name="configuration"/>.
+    /// </summary>
+    /// <param name="configuration">The application configuration to fall back to.</param>
+    /// <returns>The resolved SQL Server connection string.</returns>
+    /// <exception cref="InvalidOperationException">
+    /// Thrown when no connection string can be resolved from any of the supported sources.
+    /// </exception>
     private static string GetConnectionString(IConfiguration configuration)
     {
         // Check for full connection string first
@@ -42,6 +58,10 @@ public class DefaultSqlConnectionFactory(IConfiguration configuration)
         }
     }
 
+    /// <summary>
+    /// Creates a new, unopened <see cref="SqlConnection"/> using the resolved connection string.
+    /// </summary>
+    /// <returns>A new <see cref="SqlConnection"/> instance.</returns>
     public DbConnection CreateConnection()
     {
         return new SqlConnection(_connectionString);

web/backend/Infrastructure/Infrastructure.Repository/Sql/ISqlConnectionFactory.cs

@@ -2,7 +2,14 @@ using System.Data.Common;
 
 namespace Infrastructure.Repository.Sql;
 
+/// <summary>
+/// Factory for creating database connections used by repositories.
+/// </summary>
 public interface ISqlConnectionFactory
 {
+    /// <summary>
+    /// Creates a new, unopened database connection.
+    /// </summary>
+    /// <returns>A new <see cref="DbConnection"/> instance.</returns>
     DbConnection CreateConnection();
 }

web/backend/Infrastructure/Infrastructure.Repository/Sql/SqlConnectionStringHelper.cs

@@ -2,6 +2,9 @@ using Microsoft.Data.SqlClient;
 
 namespace Infrastructure.Repository.Sql;
 
+/// <summary>
+/// Helper for building SQL Server connection strings from environment variables.
+/// </summary>
 public static class SqlConnectionStringHelper
 {
     /// <summary>