Learning Design from Mature Coding Agents (10): Edit Tool Trade-offs — unified diff, exact edit, hashline, and whole-file
LLMs break unified diffs on bookkeeping: wrong hunk counts, hallucinated context lines. The five reference projects split into two camps — simplify the diff grammar (Codex drops line numbers), or drop diffs entirely (Claude Code/Pi/OpenCode exact replace); OMP goes further by binding read state into the format via hash anchors. rivumi took the minimal-intervention path: keep the guarded apply_patch, add a zero-fuzzy replace_text, and its qwen3:4b eval went from stable failure to 5/5.