Constant FS_OP_SYMLINK 

pub const FS_OP_SYMLINK: u8 = 4;

Create or retarget a symlink at b whose target is the verbatim string a (not a wire path; not confined to the root). base CASes on the current entry at b — a symlink’s content hash is BLAKE3-128 of its target bytes (docs/design/fs-write.md “Links”).