A '' case pattern inside a single-quoted ssh command silently breaks a watcher

A watcher that ran ssh host 'p=$(pgrep ...); case "$p" in ''|0) echo DONE;; esac' never printed DONE. The two apostrophes in '' close and reopen the local single-quoted string, so the remote shell sees in |0), which is a syntax error. Because the watcher ignored stderr and treated 'no DONE' as 'still running', it waited forever with no error shown. Use "" for the empty pattern inside single-quoted remote commands (or scp a script and run it). Also make watchers treat a non-zero ssh exit or a parse error as a distinct state, not as 'not done yet'.