Changes

• Preserve indentation of trailing injection content in 5a878e9

  Tree-sitter's code_fence_content node for indented markdown fenced code
  blocks captures trailing indent spaces as part of the content range
  (e.g. \n ). When strip_leading_indent removed those spaces, the
  resulting bare newline was lost because trailing_newlines was computed
  from the original slice (which ended in spaces, not newlines). This
  caused the closing fence to collapse onto the last line of code.

  Add trailing_newlines_with_indent to look past exact-indent trailing
  spaces when detecting trailing newlines, and re-apply indent spaces
  after the final newline during recomposition so that subsequent content
  in the parent document stays at the correct column.