0.9.89

On Pi, list_agents gains a sessionFile field for each agent: the child's session file, <timestamp>_<session id>.jsonl in the agent's session directory. The completion notice and a foreground agent's result carry the same path on a transcript: line. A user can follow a running background agent with tail -f <sessionFile> and render a finished one with pi --export <sessionFile>; before this, they had to find the file by hand. Pi writes the file once the child's first message is in and reopens it on a resume, so an agent keeps one path for its whole life, and one with no file yet lists none. @Nickonomic asked for a way to see a background agent's work while it runs (#279); this covers finding the transcript, and a live activity view follows.