Tags: Key not updated upon rename

macOS is not changing the key on tag rename

Start by reproducing the tag-rename behavior on macOS and trace where the tag key is assigned or updated. No file or test is identified in the issue, so locate the relevant rename flow before deciding on the change. Done means the key changes when a tag is renamed, with a regression test if the existing test structure supports it.

Written by the indexing model from the issue text.