Uppercase letters in username break reachable mention check in composer

zogstrip · May 13, 2026, 4:25pm

Looks like my “fix” revealed this issue for AI Agents

github.com/discourse/discourse

FIX: Suppress composer mention warning for AI bot users (#39986)

main ← fix-composer-mention-warning-ai-bots

opened 04:24PM - 13 May 26 UTC

ZogStriP

+85 -1

Mentioning an AI bot (e.g. `@Forum_Research_Assis`) in a topic the bot's User re…cord can't see — like a category restricted to a group the bot isn't part of — surfaced the "this user cannot see this mention" warning popup in the composer. The warning is misleading: AI bots reply via `PostCreator.create!(... skip_guardian: true)` (`playground.rb`), so they respond regardless of whether their User can `Guardian#can_see?` the topic. The previous case-insensitive fix (9a4cca29) exposed this latent behavior. Pre-fix, mixed-case names hit a case-sensitive hash miss in `ComposerController#mentions` and silently returned an empty `user_reasons`. Post-fix, the lookup hits correctly and the reachability check — which was always there — now fires for AI bot users that genuinely can't see the topic. Adds a `:composer_mention_user_reason` plugin modifier, applied after the standard reason is computed in `user_reason`, so plugins can clear or transform it. The AI plugin registers against the modifier and returns `nil` for any user in `DiscourseAi::AiBot::EntryPoint.all_bot_ids` (covering both AI agent users and chat-bot-enabled LLM model users). discobot and the system user are intentionally unaffected: discobot's `PostCreator.create!` does not skip the guardian, so the reachability warning remains accurate for it. https://meta.discourse.org/t/401292

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Uppercase letters in username break reachable mention check in composer

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