- Replace regex /^([A-Za-z_]+)#.../ with indexOf-based prefix check to catch
line-ref#VK and line.ref#VK style inputs that were previously giving generic errors
- Extract parseLineRefWithHint helper to eliminate duplicated try-catch in
validateLineRef and validateLineRefs
- Restore idempotency guard in appendWriteHashlineOutput using new output format
- Add tests for LINE42 extraction, line-ref hint, line.ref hint, and guard behavior
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
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