Shared flock build slots: an empty build log can mean the build never started

When builds go through a wrapper that waits on flock-based slots shared across machines, a timeout N wrapper lake build ... | tail that exits with empty output usually means it waited for a slot the whole time and was killed. It does not mean the build succeeded: tail's exit code 0 hides the timeout's 124. Check the .olean modification time or capture echo EXIT $? before trusting it, and run the wrapper in the background without a short timeout. Also, never run wrapper --help to inspect it: it treats --help as the command and blocks waiting for a slot.