feat(causality): sharpen bug_causality with git-blame (bo-8nmm)#36
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bo-s1kb v1 picked the most-recent prior commit touching a fix's files (recency+overlap). This adds SZZ-lite blame sharpening: diff the fix against its parent, blame the exact lines it removed at <fix>^, and take the dominant introducing commit as the culprit — a precise sha at higher confidence. git.rs: - blame_lines_at_rev(): blame a range at a given revision. - blame_fix_culprits(): show --unified=0 -> parse_unified_diff removed lines -> group into ranges -> blame at <fix>^. Empty for pure additions / new files / root commits (no parent). - group_consecutive() range helper + unit test. bead.rs reconstruct-causality: - Per fix commit+file, accumulate blame culprit shas; merge_causality() replaces the recency+overlap candidate per file where blame found a dominant culprit, falls back otherwise, and adds blame-only files. - blame_confidence(): floored 0.6, scales to 0.98 with blame concentration (exceeds the overlap heuristic's 0.95). Blame culprits store sha only (culprit_bead_id = None). - Degrades gracefully when not a git repo. Tests: dominant_culprit/blame_confidence/merge_causality pure units + two temp-repo integration tests (known introduced-then-fixed bug, and pure-addition -> empty). Build + clippy clean. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01GuQ96t4m1vzFQ6v72btayV
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What
Follow-up to bo-s1kb. v1 inferred a bug's culprit commit by recency+overlap (the most-recent prior commit touching the fix's files). This adds SZZ-lite git-blame sharpening: blame the exact lines a fix removed against the fix's parent to pin the precise introducing commit, at higher confidence — falling back to recency+overlap where blame can't help.
Updates
bug_causality.culprit_sha+.confidence.How
src/index/git.rsblame_lines_at_rev(rev, file, start, end)— blame a range as of a revision (not the worktree).blame_fix_culprits(fix_sha, file)—git show --unified=0→ reuseparse_unified_difffor the removed (old-side) line ranges →group_consecutive→ blame each range at<fix_sha>^. Returns oneBlameEntryper blamed line. Empty for pure-addition fixes, files newly created by the fix, or root commits (no parent).group_consecutive(lines)range helper.src/cli/bead.rs(reconstruct-causality)merge_causality(fallback, blame_map): per file, blame's dominant culprit replaces the recency+overlap candidate where available; files without blame keep the fallback; blame-only files are added.dominant_culprit(deterministic tie-break) +blame_confidence(floored 0.6, scales to 0.98 with blame concentration — above the overlap heuristic's 0.95 cap).culprit_bead_id→ None). Degrades gracefully when not a git repo.Tests
dominant_culprit(majority + ties),blame_confidenceband,merge_causality(blame overrides fallback; blame-only files added),group_consecutive.blame_fix_culpritsattributes the removed line to the introducing commit, not the fix. Plus a pure-addition → empty case.cargo test --bin bobbingreen for the touched modules; build + clippy clean.AC
✅ blame-based causality where available ✅ falls back to recency+overlap ✅ tested on a known bug.
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