tryAcquire() ran fs.existsSync(dir) on every lock acquisition to lazily create the
lock directory. The dir almost always already exists (team dirs are created up
front), so that stat was wasted on every acquire — and the file-lock path churns
heavily during a launch (inbox writes, journals, task mutations all lock per write,
showing up as unlink/open/stat syscall load in the launch profile).
Attempt the openSync('wx') directly; only on ENOENT create the directory and retry
the acquire in the same call. Same locking semantics, same files, same first-acquire
latency for a missing dir — just one fewer stat per acquire in the common case.
