pub const C2S_FS_SYNC: u8 = 0x40;Expand description
Start (or replace) a sync: [0x40][nonce:2][flags:2][latency_ms:2][inline_max:4][path_len:2][path:N]
then, when FS_SYNC_EXCLUDE is set, [exclude_len:2][exclude:M]; then,
when FS_SYNC_FROM_PTY is set, [src_pty_id:2].