Downstream report: https://phabricator.wikimedia.org/T910
Renaming a Phabricator project breaks links because Phabricator doesn't create redirects. There are two issues:
- The original hashtag is not automatically added as alternative, which breaks internal links (`#project` mentions).
- Alternative hashtags are not accepted in URLs, which breaks external links (e.g. https://phabricator.wikimedia.org/tag/MediaWiki-extensions-Flow/ which was renamed to https://phabricator.wikimedia.org/tag/flow)
Related tasks: {T6909}