Option D accurately reflects Slack Connect behavior. Slack's official developer guidance explicitly states that messages sent through an incoming webhook into a Slack Connect channel are visible to all members of that shared channel, including users participating from external organizations. Option A is incorrect because the Events API can deliver events generated by external users participating in Slack Connect channels. Developers must therefore design applications to recognize that the actor may belong to another workspace. Option B is also incorrect: Slack specifically documents that shared channels do not cause duplicate event callbacks merely because the channel spans multiple workspaces. Developers should instead inspect authorization information in event payloads to determine where the application has authorization. Option C is overly broad. Incoming webhooks can send direct messages only under specific installation-team constraints; they cannot simply DM every external participant in a shared channel. Slack Connect therefore changes assumptions about workspace ownership, user identities, channel membership, and application authorization. Applications must distinguish the workspace where the app is installed from external workspaces represented in the shared conversation. This question belongs to Apps in the Slack Platform, particularly Slack Connect architecture and app behavior in externally shared channels.