Function is_valid_storage_path 

pub fn is_valid_storage_path(value: &str) -> bool

Check whether a candidate string is an acceptable filesystem-path setting (import_directory, export_directory, dump_directory).

Rejects:

• empty / whitespace-only strings,
• strings longer than STORAGE_PATH_MAX_LEN bytes,
• strings containing a NUL byte (\0),
• strings containing a .. path component (path-traversal guard),
• strings that start with ~ (no shell-style home expansion).

The check is purely syntactic — it does not touch the filesystem.