Constant MAX_IDENTITY_FIELD_LEN 

pub const MAX_IDENTITY_FIELD_LEN: usize = 512;

Maximum length (bytes) of any source-derived string field in a StructuralIdentity. Caps the DoS / noisy-diff surface from a scanned file with a megabyte-long identifier (#1919). Generous enough for realistic Rust paths/identifiers (e.g. deeply-qualified module paths), small enough that an artifact cannot be inflated by a single field.