Hashline vs Replace: Does the Edit Format Matter?

Can Bölük's The Harness Problem showed hashline-style edits (line-number anchored, like 4#WB ) outperforming traditional replace-mode edits (old_string/new_string matching) for coding agents. I've been experimenting with building my own harness ( tau ), and wanted to verify this result and see if I should consider using hashline as the default edit strategy there. So I built edit-bench to test this myself across multiple languages and models. Setup edit-bench generates mutation-based tests from existing codebases. You point a script at a directory, and it generates mutations like deleting a statement, flipping a boolean, swapping args, etc. Languages : Python (from hive ), TypeScript (from oh-my-pi ), Rust (from irradiate ) Models : gpt-4.1-mini , google/gemini-3-flash-preview , qwen/qwen3.5-397b-a17b Edit modes : replace (old_string/new_string) vs hashline (line-number anchored) 20 tasks per language , single-attempt oneshot runs I also recently added fuzzy matching to tau (trim casca