Slack's "Only visible to you" messages aren't visible in the Matrix room.

[thomas-profitt]

To reproduce, use the Slack command "/who" in a Slack channel (not a bridged Matrix room, but using the actual Slack client) and see the "Only visible to you" message with the command's output in the Slack channel but not in the Matrix room.

[twouters]

Seems to be included in the chat.command api response, so we should probably just send it to matrix as a message from Slack (slackbot).

Some bots send replies as ephemeral messages too: https://api.slack.com/methods/chat.postEphemeral
These responses seem to work fine as is (except that they are probably visible for other matrix users...?)

[thomas-profitt]

Something else to note is that the closest thing Matrix has right now to bot messages only-visible-to-a-certain-user are messages in that user's 1:1 room with the bot. We could bridge this that way.

Maybe that's best and the only-visible-to-you bot message thing is silly.

But, our Matrix rooms representing Slack channels are meant to have one real user (the bridge's user) and a bunch of bots, so in this case, all messages are only visible to "you".