Function replace_file_with_symlink_with_override 

pub fn replace_file_with_symlink_with_override(
    source: &SafePath,
    target: &SafePath,
    dry_run: bool,
    allow_degraded: bool,
    backup_tag: &str,
    force_exdev: Option<bool>,
) -> Result<(bool, u64)>

Version of replace_file_with_symlink that accepts a per-instance EXDEV override for tests/controlled scenarios.

Errors

Returns an IO error when:

• Capability handle acquisition for the parent directory fails
• Removing the existing target fails with an unexpected errno
• Creating a snapshot (backup) of the prior state fails (Commit mode)
• Performing the atomic symlink swap fails (including EXDEV fallback when disallowed)