Switch line hashing to significance-aware seeding so meaningful lines stay stable across reflows while punctuation-only lines still disambiguate by line index.
Also narrow prefix stripping to hashline/diff patterns that reduce accidental content corruption during edit normalization.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
ab768029fa