fix(etl): address Codex MCP review findings for Phase 2

- Filter MERGE SQL columns to only include columns that exist in destination
  (allColumns and updateColumns were using unfiltered source columns)
- Fix schema-qualified table names to use proper [schema].[table] format
  instead of wrapping entire name in single brackets
- Add empty column mapping validation to throw early if no columns intersect
- Add JdeDateTransformer output column collision detection in OnInitialize
- Add TODO comment for WithCommandTimeout (stored but not yet passed to
  destinations)
- Add tests for FormatQualifiedTableName and output column collision

NEW/src/JdeScoping.DataSync/Etl/Destinations/DbBulkImportDestination.cs

@@ -62,9 +62,10 @@ public class DbBulkImportDestination : IImportDestination
         await using var connection = await _connectionFactory.CreateLotFinderConnectionAsync(cancellationToken);
 
         // Truncate destination table
+        var qualifiedName = CommonScripts.FormatQualifiedTableName(_tableName);
         await using (var truncateCmd = connection.CreateCommand())
         {
-            truncateCmd.CommandText = $"TRUNCATE TABLE [{_tableName}]";
+            truncateCmd.CommandText = $"TRUNCATE TABLE {qualifiedName}";
             truncateCmd.CommandTimeout = _commandTimeoutSeconds;
             await truncateCmd.ExecuteNonQueryAsync(cancellationToken);
         }
@@ -75,7 +76,7 @@ public class DbBulkImportDestination : IImportDestination
         // Bulk copy data
         using var bulkCopy = new SqlBulkCopy(connection)
         {
-            DestinationTableName = $"[{_tableName}]",
+            DestinationTableName = qualifiedName,
             BatchSize = _batchSize,
             BulkCopyTimeout = _commandTimeoutSeconds,
             EnableStreaming = true
@@ -91,6 +92,12 @@ public class DbBulkImportDestination : IImportDestination
             }
         }
 
+        // Validate that we have columns to work with
+        if (bulkCopy.ColumnMappings.Count == 0)
+            throw new InvalidOperationException(
+                $"No columns from source exist in destination table '{_tableName}'. " +
+                "Check column names match between source query and destination table.");
+
         // Track rows via event
         bulkCopy.NotifyAfter = _batchSize;
         bulkCopy.SqlRowsCopied += (_, e) =>

NEW/src/JdeScoping.DataSync/Etl/Destinations/DbBulkMergeDestination.cs

@@ -84,14 +84,26 @@ public class DbBulkMergeDestination : IImportDestination
             // Get destination columns for column mapping
             var destColumns = await GetDestinationColumnsAsync(connection, cancellationToken);
 
-            // Get all column names from source
+            // Get all column names from source, filtered to only include columns that exist in destination
             var allColumns = new List<string>();
             for (int i = 0; i < source.FieldCount; i++)
-                allColumns.Add(source.GetName(i));
+            {
+                var colName = source.GetName(i);
+                if (destColumns.Contains(colName))
+                    allColumns.Add(colName);
+            }
 
-            // Determine update columns (all non-match columns if not specified)
+            // Validate that we have columns to work with
+            if (allColumns.Count == 0)
+                throw new InvalidOperationException(
+                    $"No columns from source exist in destination table '{_tableName}'. " +
+                    "Check column names match between source query and destination table.");
+
+            // Determine update columns (all non-match columns if not specified), filtered to destColumns
             var matchSet = new HashSet<string>(_matchColumns, StringComparer.OrdinalIgnoreCase);
-            var updateCols = _updateColumns ?? allColumns.Where(c => !matchSet.Contains(c)).ToArray();
+            var updateCols = (_updateColumns ?? allColumns.Where(c => !matchSet.Contains(c)).ToArray())
+                .Where(c => destColumns.Contains(c))
+                .ToArray();
 
             // Build MERGE SQL
             var mergeSql = BuildMergeSql(tempTableName, allColumns, updateCols);
@@ -135,7 +147,8 @@ public class DbBulkMergeDestination : IImportDestination
 
     private async Task CreateTempTableAsync(SqlConnection connection, string tempTableName, CancellationToken ct)
     {
-        var sql = $"SELECT TOP 0 * INTO {tempTableName} FROM [{_tableName}]";
+        var qualifiedName = CommonScripts.FormatQualifiedTableName(_tableName);
+        var sql = $"SELECT TOP 0 * INTO {tempTableName} FROM {qualifiedName}";
         await using var cmd = connection.CreateCommand();
         cmd.CommandText = sql;
         cmd.CommandTimeout = _commandTimeoutSeconds;
@@ -199,8 +212,9 @@ public class DbBulkMergeDestination : IImportDestination
 
     private string BuildMergeSql(string tempTableName, IReadOnlyList<string> allColumns, IReadOnlyList<string> updateColumns)
     {
+        var qualifiedName = CommonScripts.FormatQualifiedTableName(_tableName);
         var sb = new StringBuilder();
-        sb.AppendLine($"MERGE INTO [{_tableName}] AS target");
+        sb.AppendLine($"MERGE INTO {qualifiedName} AS target");
         sb.AppendLine($"USING {tempTableName} AS source");
         sb.Append("ON ");
         sb.AppendLine(string.Join(" AND ", _matchColumns.Select(c => $"target.[{c}] = source.[{c}]")));

NEW/src/JdeScoping.DataSync/Etl/Pipeline/EtlPipelineBuilder.cs

@@ -60,6 +60,9 @@ public class EtlPipelineBuilder
         return this;
     }
 
+    // TODO: Currently this timeout value is stored but not passed to destinations.
+    // In the future, the pipeline should pass this timeout to destinations that support it.
+    // For now, destinations use their own default timeout (600 seconds).
     public EtlPipelineBuilder WithCommandTimeout(TimeSpan timeout)
     {
         if (timeout < TimeSpan.Zero || timeout > TimeSpan.FromHours(24))

NEW/src/JdeScoping.DataSync/Etl/Scripts/CommonScripts.cs

@@ -18,6 +18,15 @@ public static class CommonScripts
             : ("dbo", parts[0]);
     }
 
+    /// <summary>
+    /// Formats a table name as a properly quoted [schema].[table] identifier.
+    /// </summary>
+    public static string FormatQualifiedTableName(string tableName)
+    {
+        var (schema, table) = ParseTableName(tableName);
+        return $"[{schema}].[{table}]";
+    }
+
     public static IScriptRunner DisableIndexes(
         IDbConnectionFactory factory,
         string tableName,

NEW/src/JdeScoping.DataSync/Etl/Transformers/JdeDateTransformer.cs

@@ -56,6 +56,20 @@ public class JdeDateTransformer : DataTransformerBase
         _dateOrdinal = source.GetOrdinal(_dateColumn);
         _timeOrdinal = source.GetOrdinal(_timeColumn);
 
+        // Validate output column name doesn't conflict with existing columns
+        // (excluding the date and time columns which will be replaced/removed)
+        for (int i = 0; i < source.FieldCount; i++)
+        {
+            if (i == _dateOrdinal || i == _timeOrdinal) continue;
+            var existingName = source.GetName(i);
+            if (string.Equals(existingName, _outputColumn, StringComparison.OrdinalIgnoreCase))
+            {
+                throw new InvalidOperationException(
+                    $"Output column name '{_outputColumn}' conflicts with existing column '{existingName}'. " +
+                    "Choose a different output column name.");
+            }
+        }
+
         var ordinalList = new List<int>();
         var nameList = new List<string>();
         _nameToOrdinal = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);

NEW/tests/JdeScoping.DataSync.Tests/Etl/Scripts/CommonScriptsTests.cs

@@ -98,4 +98,20 @@ public class CommonScriptsTests
         Assert.Equal("TimeoutScript", runner.ScriptName);
         Assert.NotNull(runner);
     }
+
+    [Theory]
+    [InlineData("WorkOrder", "[dbo].[WorkOrder]")]
+    [InlineData("dbo.WorkOrder", "[dbo].[WorkOrder]")]
+    [InlineData("[dbo].[WorkOrder]", "[dbo].[WorkOrder]")]
+    [InlineData("Config.Settings", "[Config].[Settings]")]
+    [InlineData("[Config].[Settings]", "[Config].[Settings]")]
+    [InlineData("myschema.MyTable", "[myschema].[MyTable]")]
+    public void FormatQualifiedTableName_VariousFormats_FormatsCorrectly(string input, string expected)
+    {
+        // Act
+        var result = CommonScripts.FormatQualifiedTableName(input);
+
+        // Assert
+        Assert.Equal(expected, result);
+    }
 }

NEW/tests/JdeScoping.DataSync.Tests/Etl/Transformers/JdeDateTransformerTests.cs

@@ -240,6 +240,46 @@ public class JdeDateTransformerTests
         Assert.Equal(sentinel, result);
     }
 
+    [Fact]
+    public void OutputColumnConflictsWithExistingColumn_ThrowsInvalidOperationException()
+    {
+        // Arrange - "Name" column exists and we try to use it as output
+        var source = CreateMockReader(new[] { "Id", "UPMJ", "TDAY", "Name" }, new object[] { 1, 124001m, 120000m, "Test" });
+        var transformer = new JdeDateTransformer("UPMJ", "TDAY", "Name"); // "Name" conflicts
+
+        // Act & Assert
+        var ex = Assert.Throws<InvalidOperationException>(() => transformer.Transform(source));
+        Assert.Contains("conflicts with existing column", ex.Message);
+    }
+
+    [Fact]
+    public void OutputColumnMatchesDateColumn_Succeeds()
+    {
+        // Arrange - output column can match the date column name (it replaces it)
+        var source = CreateMockReader(new[] { "Id", "UPMJ", "TDAY", "Name" }, new object[] { 1, 124001m, 120000m, "Test" });
+        var transformer = new JdeDateTransformer("UPMJ", "TDAY", "UPMJ"); // Same as date column
+
+        // Act - should not throw
+        var reader = transformer.Transform(source);
+
+        // Assert
+        Assert.Equal("UPMJ", reader.GetName(1)); // Still named UPMJ
+    }
+
+    [Fact]
+    public void OutputColumnMatchesTimeColumn_Succeeds()
+    {
+        // Arrange - output column can match the time column name (it's removed anyway)
+        var source = CreateMockReader(new[] { "Id", "UPMJ", "TDAY", "Name" }, new object[] { 1, 124001m, 120000m, "Test" });
+        var transformer = new JdeDateTransformer("UPMJ", "TDAY", "TDAY"); // Same as time column
+
+        // Act - should not throw
+        var reader = transformer.Transform(source);
+
+        // Assert
+        Assert.Equal(3, reader.FieldCount); // One column removed
+    }
+
     private static IDataReader CreateMockReader(string[] columns, object[] values)
     {
         var reader = Substitute.For<IDataReader>();