Yeah, that’s not pretty:
ActionView::Template::Error (No route matches {action: "tag_feed", controller: "tags", tag_id: "9999"})
app/views/list/list.erb:136
app/views/list/list.erb:134
lib/topic_list_responder.rb:16:in 'block (2 levels) in TopicListResponder#respond_with_list'
lib/topic_list_responder.rb:7:in 'TopicListResponder#respond_with_list'
app/controllers/tags_controller.rb:223:in 'block (2 levels) in <class:TagsController>'
app/controllers/tags_controller.rb:229:in 'TagsController#show'
app/controllers/application_controller.rb:447:in 'block in ApplicationController#with_resolved_locale'
app/controllers/application_controller.rb:447:in 'ApplicationController#with_resolved_locale'
app/controllers/application_controller.rb:1098:in 'ApplicationController#ensure_dont_cache_page'
lib/middleware/omniauth_bypass_middleware.rb:35:in 'Middleware::OmniauthBypassMiddleware#call'
…
We should fix that error; we also might be able to fallback to looking for an all-numeric tag name if the tag id isn’t found.
Wayback first noticed that tag appearing on 2025-05-13 and its url was https://retrocomputingforum.com/tag/6309 which worked at the time and up until 2025-12-16.

