Where Bugs Live — act101 Agent Skill

Where Bugs Live

Use when you need the riskiest code in a repository, where bugs are most likely to live. Combines git churn, complexity, co-change coupling, and ownership concentration into one ranked, explained list.

Where Bugs Live

Rank the code most likely to harbor defects. Bugs cluster where code changes often, is complex, is entangled with other code, and is owned by few people.

When to use

Prioritizing a code-review, test-writing, or refactoring effort on a large codebase.
Onboarding to an unfamiliar repo and wanting to know where the landmines are.
Triaging technical debt with evidence.

Inputs

A git repository with history for the three git overlays: churn_hotspots (workspace mode), co_change_clusters, and ownership_map, all Architecture tier. analyze_hotspots is static (Engineering) and needs no git.

Protocol

Churn: churn_hotspots in workspace mode (no file) ranks symbols by recency-weighted change frequency.
Complexity: analyze_hotspots ranks files by composite complexity (cyclomatic, statements, nesting).
Coupling: co_change_clusters finds symbols that change together. Hidden coupling means a fix in one place needs a fix in another.
Ownership: ownership_map finds low-bus-factor symbols.
Synthesize: intersect and rank. A symbol that is high-churn, complex, in a co-change cluster, and low-bus-factor is a top risk. For each entry name the signals that fired and why they matter, with the symbol id and file.

Output

A ranked, explained risk list. Each item: symbol or file, the firing signals (churn score, complexity, co-change members, bus factor), and a one-line reason. Lead with the entries where the most signals agree.

Coverage

For grammars without symbol extraction, churn, co-change, and ownership degrade to file level. Each response's modeled_kinds shows whether symbol extraction was modeled; when it was not, report file-level precision as such. Churn and ownership are git facts; complexity is a syntactic estimate.