while understanding add_index_entry_with_check() i got to do_invalidate_path(). the commit hash for do_invalidate_path() function is `749864627c2d3c33bbc56d7ba0b5542af698cc40` in the commit message it is explained that, cache-tree is used to store object names of index file objects and it is kept separate from index file because adding it would change index file format. the part i couldn't understand is: "During various index manupulations, we selectively invalidate the parts so that the next write-tree can bypass regenerating tree objects for unchanged parts of the directory hierarchy." what exactly does invalidating means here ?
