When starting crew without mayor running, tmux has-session can return
"no current target" if no tmux server exists. This error was not
mapped to ErrNoServer, causing crew start to fail instead of
bootstrapping a new tmux server.
Add "no current target" to the ErrNoServer detection so crew (and
other agents) can start independently without requiring an existing
tmux session.
Reproduction:
- Ensure no tmux server running (tmux kill-server)
- Run: gt crew start <rig>/<name>
- Before fix: "Error: checking session: tmux has-session: no current target"
- After fix: Crew session starts successfully
Co-authored-by: Shaun <TechnicallyShaun@users.noreply.github.com>
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