We cannot assume who among the SUT operators are working on a specific test run. To avoid the SUT operators to deal with too many channels they do not care about, we will rather other the interested SUT operator to join the channel.
When a user is not yet part of the channel, instead of the permanent link to the test run channel, add a "join" button.
When the SUT operator hits the "join" button, it is automatically added to the channel; then the link to the channel can be displayed.
Users will be able to leave the channel from the GUI of the communication tool, no need to implement this feature.
A SUT operator who is allowed to access a test run can see the "join" button.
When the "join" button is clicked, the link to the channel is displayed and the SUT operator is allowed to access it in the communication tool.