// agent_files/io.rs — boundary module for direct filesystem operations.
// Exempt from forbid_io_effects because the file stem is `io`.
/// Check if a file contains a specific marker string using std::fs.
///
/// This is the non-workspace version that operates on absolute paths
/// outside the workspace abstraction (e.g., `.git/hooks/`).
///
/// Returns `Ok(true)` if the marker is found, `Ok(false)` if not found or file doesn't exist.
///
/// # Errors
///
/// Returns error if the operation fails.