Fix charset validation context handling and enum regression

- Use WithContext pattern to preserve *sql.Context type for enum validation
- Add ellipses truncation test case for long invalid byte sequences
- Clean up overbloated comments to focus on why vs what
- Ensure both charset and enum validation work with MySQL compatibility

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: elianddb

enginetest/queries/script_queries.go

@@ -7162,6 +7162,10 @@ where
 					{types.OkResult{RowsAffected: 1}},
 				},
 			},
+			{
+				Query:          "insert into t(c) values (X'999897969594939291');",
+				ExpectedErrStr: "Incorrect string value: '\\x99\\x98\\x97\\x96\\x95\\x94...' for column 'c' at row 1",
+			},
 		},
 	},
 	{

sql/rowexec/insert.go

@@ -113,10 +113,10 @@ func (i *insertIter) Next(ctx *sql.Context) (returnRow sql.Row, returnErr error)
 	// Do any necessary type conversions to the target schema
 	for idx, col := range i.schema {
 		if row[idx] != nil {
-			// Add column name and row number to context for proper error messages
-			ctxWithColumnInfo := context.WithValue(ctx, types.ColumnNameKey, col.Name)
-			ctxWithColumnInfo = context.WithValue(ctxWithColumnInfo, types.RowNumberKey, i.rowNumber)
-
+			// Add column/row context for charset error messages
+			ctxWithValues := context.WithValue(ctx.Context, types.ColumnNameKey, col.Name)
+			ctxWithValues = context.WithValue(ctxWithValues, types.RowNumberKey, i.rowNumber)
+			ctxWithColumnInfo := ctx.WithContext(ctxWithValues)
 			converted, inRange, cErr := col.Type.Convert(ctxWithColumnInfo, row[idx])
 			if cErr == nil && !inRange {
 				cErr = sql.ErrValueOutOfRange.New(row[idx], col.Type)

sql/types/enum.go

@@ -172,6 +172,8 @@ func (t EnumType) Convert(ctx context.Context, v interface{}) (interface{}, sql.
 		if _, ok := t.At(value); ok {
 			return uint16(value), sql.InRange, nil
 		}
+		// If value is not a valid enum index, return error
+		return nil, sql.OutOfRange, ErrConvertingToEnum.New(value)
 	case uint:
 		return t.Convert(ctx, int(value))
 	case int8:
@@ -185,6 +187,8 @@ func (t EnumType) Convert(ctx context.Context, v interface{}) (interface{}, sql.
 		if _, ok := t.At(int(value)); ok {
 			return value, sql.InRange, nil
 		}
+		// If value is not a valid enum index, return error
+		return nil, sql.OutOfRange, ErrConvertingToEnum.New(value)
 	case int32:
 		return t.Convert(ctx, int(value))
 	case uint32:

sql/types/strings.go

@@ -514,7 +514,6 @@ func ConvertToBytes(ctx context.Context, v interface{}, t sql.StringType, dest [
 }
 
 // getColumnContext extracts column name and row number from context.
-// Returns defaults if context values are not available.
 func getColumnContext(ctx context.Context) (string, int64) {
 	colName := "<unknown>"
 	rowNum := int64(0)
@@ -526,12 +525,12 @@ func getColumnContext(ctx context.Context) (string, int64) {
 		rowNum = num
 	}
 
+
 	return colName, rowNum
 }
 
-// formatInvalidByteForError formats invalid bytes for error messages to match MySQL behavior exactly.
-// MySQL shows all consecutive invalid bytes starting from the first invalid byte position.
-// When there are many invalid bytes, MySQL truncates with "..." after showing several bytes.
+// formatInvalidByteForError formats invalid bytes for MySQL-compatible error messages.
+// Shows consecutive invalid bytes, truncating with "..." after 6 bytes.
 func formatInvalidByteForError(bytesVal []byte) string {
 	if len(bytesVal) == 0 {
 		return fallbackInvalidByte