- Added `toArray()` helper function to normalize `string | string[]` inputs for hashline edit operations with comma-separated line reference support.
- Added `HashlineMismatchError` class that displays grep-style output with `>>>` markers for hash validation failures.
- Added `HashMismatch` type for representing individual hash mismatches with line number, expected hash, and actual hash.
- Updated `HashlineEdit` type to accept `string | string[]` for `old` and `new` fields, allowing both singular and plural input formats.
- Reduced hash length from 4 to 2 hex characters (16-bit hashes) for more concise line references.
- Enhanced `parseLineRef()` to strip display-format suffixes and `validateLineRef()` to throw `HashlineMismatchError` with context lines for better error reporting.