feat(enrichment): blame-to-PR regression linker analyzer (#2034)

[nickmopen]

Closes #2034 (part of #1499).

New REES github-light analyzer: for files a PR modifies or deletes, it resolves which prior PR most recently introduced that region and surfaces it — giving the reviewer instant context on what the change is altering. Not per-line blame (no checkout/blame API): it attributes each touched file's most recent base-branch commit and maps it to its PR. Bounded and fail-safe.

Deliverables

• review-enrichment/src/types.ts — BlameLinkFinding ({ file, line, introducedByPr?, introducedByShaPrefix? }, SHA prefix only, never contents) + blameLink? on BriefFindings.
• review-enrichment/src/analyzers/blame-link.ts — firstTouchedOldLine() parses the unified-diff patch for a representative modified/deleted old line; per file it reads the path's most recent commit on baseSha and maps it to a PR via the commit→PR association API (injected fetch). Strict maxFilesProbed (6) + maxLookups (12) caps; emits partial on cap; skips added files & pure additions (nothing to blame); no-token / bad-slug / fetch-error → no finding, never throws.
• registry.ts — descriptor (category: history, cost: github-light, requires: ['files','github-token']) with an inline render().
• render.ts — dispatches the blameLink section via renderDescriptorSection.
• Regenerated analyzer-metadata.json, .env.example, and the UI metadata; added blameLink to the registry meta-test's expected list.
• test/blame-link.test.ts — resolved originating PR (+ brief render), SHA-only fallback, unresolvable line (no finding), added/pure-addition skip, file-probe cap, and token-absent skip; plus pure firstTouchedOldLine cases.

Validation

Full review-enrichment suite (build + sourcemaps + metadata --check + node:test):

ℹ tests 400
ℹ pass 400
ℹ fail 0

Includes the 7 blame-link tests and the "generated analyzer metadata matches the runtime registry and profiles" check, so the metadata/.env/UI regeneration is consistent with the descriptor.

[loopover-orb]

Warning

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⏸️ Gittensory review result - manual review recommended

_{Review updated: 2026-07-02 23:16:50 UTC}

9 files · 1 AI reviewer · no blockers · readiness 60/100 · CI green · clean

⏸️ Suggested Action - Manual Review

Review summary
This adds a bounded REES analyzer that turns changed-file patches into file-level last-touch history and wires it through the registry, generated metadata, render path, and tests. The implementation is coherent with the existing churn-hotspot analyzer pattern: it skips added/generated files, anchors lookups to the base SHA, falls back to a SHA prefix when the commit has no associated PR, and keeps the rendered copy from claiming per-line blame. I do not see a reachable correctness break in the visible diff.

Nits — 5 non-blocking

• nit: review-enrichment/src/analyzers/blame-link.ts:163 skips generated/binary paths using the displayed `file.path`, but for renamed files the actual lookup is `previousPath`, so a generated old path renamed into a normal-looking path can still spend GitHub calls; consider checking `lookupPath` before enqueueing renamed candidates.
• nit: review-enrichment/src/analyzers/blame-link.ts:186 pushes a finding when the PR lookup is skipped by the lookup cap, which is intentional, but there is no explicit marker that the PR association was not attempted versus absent; consider a small internal comment or test assertion for that cap-edge fallback so future refactors preserve the distinction.
• In review-enrichment/src/analyzers/blame-link.ts:163, compute `lookupPath` before the skip decision for renamed files and apply `SKIP_RE` to the path actually queried.
• Add a focused test for the `lookups === MAX_LOOKUPS - 1` edge in review-enrichment/test/blame-link.test.ts so the SHA-only partial result path stays covered.
• 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	#2034
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: the review lane is unavailable, so it is not ready for automated review.
Contributor workload	✅ 10/10	Author activity: 100 registered-repo PR(s), 65 merged, 1 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	nickmopen; Gittensor profile; 100 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: 100 PR(s), 1 issue(s).
• Related work: Items reference the same linked issue feat(enrichment): blame-to-PR regression linker analyzer #2034. (issue #2034)
• Related work: Open PR work references issue feat(enrichment): blame-to-PR regression linker analyzer #2034. (issue #2034)
• Related work: Titles/paths share 8 meaningful terms. (issue #2033, issue #2024)
• Additional title-only matches omitted; title-only overlap does not block.

Contributor next steps

• Review top overlaps.
• Add a concise scope and risk note.
• Await review-lane availability.
• 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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