maxAgentTerminals now counts only running Agent-controlled terminals and
pending Agent allocations, each id once; exited terminals and failed
allocations awaiting cleanup still count toward maxTerminals. openForAgent
applies rename's 1-120 character title rule and trims the title.
readScreen reports a terminal closed while its read drains as
RemoteError terminal/unavailable, like a missing terminal.
Yichen Jiang
f1e90e5845