Very simple tool to send Slack messages. Built into a docker image
Mentioning users who aren't in the channel
When the message tags a Slack user (<@U...>) who is not a member of the target
channel, the mention is otherwise silent. Set SLACK_MENTION_MEMBERSHIP_MODE to
act on every user tagged in the message:
none (default) — do nothing, current behavior.
invite — invite the tagged users to the channel. Requires the
channels:write.invites (public) or groups:write (private) scope, and the
bot must already be a member of the channel (otherwise the invite fails with
not_in_channel).
notify — DM each tagged user a link to the channel. Requires im:write and
chat:write. The DM is always sent; membership is not checked first.
Failures here are logged but never fail the run — posting the message is the
primary success.