<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Label this issue](https://contributors.gitlab.com/manage-issue?action=label&projectId=278964&issueIid=592145) </details> <!--IssueSummary end--> ## Problem to solve The `/blocked_by` and `/blocks` quick actions for work item dependencies for both Issue and MergeRequest currently lack reference validation as discussed in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/207136#note_3114431096. When users provide invalid or non-existent work item references, the commands fail silently without providing feedback. ## Proposal We need to ensure the passed-in references are valid. If not, we need to return an error message to communicate that to the user. Since we may have multiple references, we need to show successful messages and failed messages together if it fails partially. ### Example scenarios: - `/blocks !123 !456 !789` where `!456` doesn't exist -> Show success for `!123` and `!789`, error for `!456` - `/blocked_by !100 !200` where both are invalid -> Show errors for both references - `/blocks !123` where `!123` is valid -> Show success message only