Function pin_snapshot_worktree_state 

pub fn pin_snapshot_worktree_state(
    snapshot: &mut ComposeSnapshot,
    dir: &str,
) -> Result<()>

Pin each snapshot file’s worktree state into the object database.

Records (mode, oid) per path as of this moment, so whole-file staging later reproduces exactly this content regardless of subsequent worktree edits. Paths absent from the worktree are pinned as deletions.