The bead description mentioned compile errors in hash.rs from API drift,
but those errors were either already fixed or misattributed. The API usage
was already correct:
- compute_fingerprint already takes 3 arguments with source
- len() already propagates Result with ?
- read_at method already used correctly
- Catalog fields accessed via trailer correctly
Only cleanup: removed unused std::fs::File and std::io imports.
Verification: notes/bf-4mkhv.md
