grep -cv (and grep -v) return exit code 1 when there are zero matches.
With set -euo pipefail this silently aborted the script before count
was returned — causing 'agent.sh new' to fail on a fresh repo with no
existing worktrees.
Fix: move the grep -v into worktree_paths with '|| true' so the
function always exits 0, then derive worktree_count via wc -l.
Refactor [ test ] && prefail pattern to if/then/fi — set -euo pipefail
was silently exiting after the loop because the failing-test compound
propagated exit code 1 through the function return.
Add ERR trap so future silent fails get diagnosed at the source.
Oskar Kapala