service/dangerzone.md

-The "dangerzone" service is a documentation sanitization system based
+The "dangerzone" service was a documentation sanitization system based
 on the [Dangerzone][] project, using [Nextcloud][] as a frontend.
 
+It was retired in 2025 because users had moved to other tools, see
+[TPA-RFC-78][].
+
+This documentation is kept for historical reference.
+
 [Dangerzone]: https://dangerzone.rocks/
 [Nextcloud]: service/nextcloud
+[TPA-RFC-78]: https://gitlab.torproject.org/tpo/tpa/team/-/wikis/policy/tpa-rfc-78-dangerzone-retirement
 
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