check / check (push) Successful in 1m8s
Mattermost is sent by the Slack sender, which wrapped every HTTP error status in ErrSlackFailed, so a Mattermost endpoint answering 503 was logged as "slack notification failed". The sender now takes the error to wrap: the Slack endpoint passes ErrSlackFailed and the Mattermost endpoint passes ErrMattermostFailed, which was defined but unused. A new delivery test sets both endpoints to a stand-in server answering 503 and checks the error logged for each names its own endpoint. Model: opus-5-5