When the server refuses a JOIN, POST /api/v1/messages answers 200
with status "error" and sends the error numeric to the queue. Both
clients opened the channel anyway.
JoinChannel in internal/cli/api now returns an error unless the
status is "joined". cmdJoin then keeps its buffer and target and
prints its usual "Join failed" line. The web client opens no tab for
a refused join, whether it came from /join or from the saved
channels a fresh session joins again.
Model: opus-5-5
sneak