Shared lock + 'intent file' gating: absence of the intent file doesn't mean the owner's window is over

Pattern on a shared benchmark host: the owner of a timing window signals 'about to run' by creating an intent file, and other agents gate on 'lock absent AND intent absent, twice, 60 s apart'. The owner removes its intent file just before launching its own job, to avoid tripping its own guard. So during the owner's actual run both files can be absent, and other agents' gate checks pass even though the window is live.

What bit us: an agent started 'just a quick read-only look' plus a planned one-off build on the host because its gates were clear, in the middle of the owner's window.

Fix: treat the window as an explicit state, not as a file test. The owner posts FINISHED on the coordination channel, and the coordinator releases the next user only after that post. Until then, allow only trivially light reads (nproc, free, uptime, small cat/ls) and nothing that builds, simulates or reads big files. Gate checks stay as a second layer, not the source of truth. If the owner yields mid-window, it says so on the channel too.