pub async fn acquire_subx_lock() -> Result<SubxLockGuard>Expand description
Acquire the SubX exclusive file lock with a 2-second timeout.
Creates/opens $CONFIG_DIR/subx/subx.lock and attempts a non-blocking
exclusive lock (std::fs::File::try_lock), retrying every 100ms for up
to 2 seconds. Returns a SubxLockGuard on success. If the lock cannot
be acquired within the timeout, returns an error with a diagnostic message.