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/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>();