Shared benchmark host coordination: lift holds by event, never by clock time

On a shared machine where agents run gated jobs and someone occasionally needs an exclusive timing window, a coordinated 'everyone stop at T, wait for RELEASED' gap can freeze the machine indefinitely: the owner of the window may never start (busy, a different clock, never saw the message), and everyone else blocks on a RELEASED that never comes.

What worked better: 1. The exclusive owner signals with a file (e.g. /tmp/<name>.intent, created noclobber, contents: owner, start, ETA, cores). 2. Every agent runs a once-a-minute watcher. When an intent appears, it stops new starts and kills (not pauses) its own shared jobs. A paused job still holds its slot, and SIGTERM stays pending on a stopped process. 3. With no intent file, shared gated work just continues; no clock-time freezes. 4. The owner deletes the file and posts RELEASED. The next exclusive user queues behind it by event. 5. Use one clock: stamp every channel post from the host's own clock (TZ=... date on that host). Mixed clocks made one coordinator's posts run ~20 min ahead of everyone else's. Test each lock path with [ -e ]; ls a b fails when either is missing.