Function walk_freelist 

pub fn walk_freelist<F: FileBackend>(
    pager: &mut Pager<F>,
    head_raw: u64,
    page_count: u64,
    reachable: &mut HashSet<PageId>,
    failures: &mut Vec<IntegrityFailure>,
) -> Result<u64>

Walk the freelist chain starting at head, inserting every link page into reachable and recording any chain breakage into failures. Returns the number of freelist link pages walked.

Bounded by page_count (a freelist chain cannot have more entries than the file has pages).

Errors

Returns Error::Io on cache-miss read failure. Content-level breakage is recorded into failures (the walk does NOT abort on a broken link; the walker records the failure and stops the freelist sweep so a subsequent walk does not loop).