feat(enrichment): churn-hotspot analyzer

[nickmopen]

Summary

Adds a REES analyzer (#1513) that flags the files a PR changes which are statistical fragility hotspots — a high recent commit frequency and a high fraction of fix/revert commits — so the reviewer scrutinizes areas where defects historically cluster. Additive + fail-safe; fills its own churnHotspot findings key.

Detects (counts from the public commit log only — never file contents)

• For each changed file (skipping newly-added, lockfiles, generated output, and binaries), reads one page of the file's commit history over a 90-day window via the GitHub commits API.
• Counts the commits and classifies each subject line as a fix/revert (fix/bugfix/hotfix/revert/regression).
• Reports a file with ≥ 8 commits and ≥ 30% fixes, with the commit count (+ when the page cap is hit), fix count, and window.

Distinct from the history analyzer (#1478), which scores the author's track record; this scores the change area's defect density.

Implementation (established review-enrichment/ pattern)

1. ChurnHotspotFinding type + churnHotspot? key in src/types.ts
2. src/analyzers/churn-hotspot.ts — pure helpers (isFixCommit, summarizeChurn, isHotspot) + scanChurnHotspot(req, fetch, opts), using the shared boundedFetchJson
3. Registered as a descriptor in src/analyzers/registry.ts (category: history, cost: github-heavy, requires: files + github-token)
4. Public-safe block in src/render.ts
5. node:test units in a separate test/churn-hotspot.test.ts; analyzer-metadata.json + the descriptor-derived lists regenerated via npm run metadata

Validation

From review-enrichment/ (Node 24):

npm test   # build + metadata check + node --test: 299 pass / 0 fail

Covers fix-subject classification (incl. lookalikes like prefix/fixture/suffix that must NOT match, and body-vs-subject), count/fraction/threshold logic, hotspot vs low-churn/low-fix, the page-cap (capped) flag, skipping lockfiles/binaries/added files without fetching, token/slug guards, non-ok/throwing-fetch fail-safe, abort, and the rendered block.

Closes #1513

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✅ Gittensory review result - approve/merge recommended

_{Review updated: 2026-06-30 19:18:03 UTC}

9 files · 1 AI reviewer · no blockers · readiness 55/100 · CI green · unknown

✅ Suggested Action - Approve/Merge

• safe to merge

Review summary
This adds a coherent REES churn-hotspot analyzer, registers it, exposes generated metadata/UI docs, and renders a public-safe finding block. The core path is fail-safe and bounded, and the pure helper tests cover the thresholding and subject-line classification well enough for the visible behavior. The notable limitation is that the GitHub commits lookup is intentionally shallow and branch-defaulted, but that matches the stated one-page/public-log design rather than breaking the implementation.

Nits — 6 non-blocking

• nit: review-enrichment/src/analyzers/churn-hotspot.ts:105 uses `Date.now()` directly, which makes the exact `since` query hard to assert in tests; injecting the clock through options would make this analyzer easier to regression-test.
• nit: review-enrichment/src/analyzers/churn-hotspot.ts:27 does not classify `bug:` conventional-commit subjects as fixes, so the analyzer may undercount projects that use `bug:` rather than `fix:` or `bugfix`.
• nit: review-enrichment/test/churn-hotspot.test.ts:38 only verifies the happy-path fetch result and not the generated GitHub URL parameters, so regressions in `path`, `since`, or `per_page` wiring could slip through.
• review-enrichment/src/analyzers/churn-hotspot.ts:105: add an optional `nowMs` or clock in `ScanOptions` and assert the resulting `since` query in `review-enrichment/test/churn-hotspot.test.ts`.
• review-enrichment/src/analyzers/churn-hotspot.ts:27: consider whether `bug:` should be included in `FIX_RE`, or document why this analyzer intentionally requires `fix`/`bugfix` wording.
• Readiness score is below the configured threshold — Use the readiness panel as advisory maintainer context; the score does not block this PR.

Signal	Result	Evidence
Code review	✅ No blockers	1 reviewer
Linked issue	✅ Linked	#1513
Related work	⚠️ 3 scoped overlaps	Top overlaps are listed below; lower-confidence bulk is hidden.
Change scope	❌ 8/20	High review scope from cached public metadata (size label size:L; 1 linked issue).
Validation posture	❌ 5/25	Preflight is holding this PR; address the blocker before review.
Contributor workload	✅ 10/10	Author activity: 90 registered-repo PR(s), 61 merged, 1 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	nickmopen; Gittensor profile; 90 PR(s), 1 issue(s).
Gate result	✅ Passing	No configured blocker found.

Review context

• Author: nickmopen
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository registration is not available in the local Gittensory cache.
• Public profile languages: not available
• Official Gittensor activity: 90 PR(s), 1 issue(s).
• Related work: Items reference the same linked issue feat(enrichment): Churn-hotspot + bug-density scorer #1513. (issue #1513)
• Related work: Open PR work references issue feat(enrichment): Churn-hotspot + bug-density scorer #1513. (issue #1513)
• Related work: Titles/paths share 5 meaningful terms. (issue #1477)
• Additional title-only matches omitted; title-only overlap does not block.

Contributor next steps

• Review top overlaps.
• Add a concise scope and risk note.
• Fix the blocker.
• Triage stale or unlinked PRs.
• Refresh registry data or choose a registered active repo.
• Check active issues and PRs before submitting.

Signal definitions

• Related work = same linked issue, overlapping active PRs, or title/path similarity.
• Change scope = cached public metadata such as size labels, draft state, and review-burden hints.
• Validation posture = whether the PR provides enough public validation/test evidence for maintainer review.
• Contributor workload = public contributor activity and cleanup pressure, not a repo-wide quality failure.
• Contributor context = public GitHub/Gittensor identity context; non-Gittensor status is not a blocker.

_{🟩 Safe / merged · 🟦 Advisory · 🟨 Held for review · 🟥 Blocked / closed}

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