feat(signals): slop signal — no linked issue without rationale (#562)

[jaso0n0818]

Summary

Implements the no-linked-issue-without-rationale deterministic slop signal (#562) — the remaining sibling of the #563 (duplicate-cluster) and #564 (generic/empty commit) deterministic signals.

Behaviour

buildNoLinkedIssueRationaleFinding fires only when all hold (high-precision, false-positive-averse like the other deterministic signals):

• the caller reports no linked issue (hasLinkedIssue: false — absent/undefined data is never a signal),
• the PR body carries no clear no-issue rationale, and
• the repo is not in the issue-discovery lane (issueDiscoveryLane !== true), where unlinked PRs are expected.

Weighted 15 — a traceability/weak-effort signal, consistent with emptyDescription / lowQualityCommitMessage.

Reuse

Reuses hasClearNoIssueRationale (now exported from signals/engine.ts) so this signal and the public PR-panel traceability check share one definition of a rationale (maintenance / docs-only / "no issue: …").

Surface

Threaded through the /v1/lint/slop-risk route and the check_slop_risk MCP tool via two new optional inputs (hasLinkedIssue, issueDiscoveryLane); deterministic, metadata-only, public-safe output preserved.

Testing

• npx vitest run test/unit/slop.test.ts → 34 passed (3 new feat(signals): slop signal — no linked issue without rationale #562 cases)
• npx tsc --noEmit → clean
• git diff --check → clean

Closes #562.

[ghost]

🔍 Maintainer review

Reviewed 5 file(s) — ✅ all CI green.

Suggested action: ✅ Safe to merge — both reviewers found no blocking issues.

Reviewer A · gpt-oss-120b — recommends ✅ merge
The change adds a well‑scoped slop signal for PRs that lack a linked issue and a clear rationale. Types are extended safely, the new helper is exported for shared use, schemas are updated with optional fields, and comprehensive unit tests cover the new behavior. No security or public‑private boundary violations are introduced, and existing functionality is unaffected. CI failures are not reported. Minor nit: ensure the test file imports FORBIDDEN_PUBLIC_TERMS if not already present.

Suggestions

• Verify that FORBIDDEN_PUBLIC_TERMS is imported in test/unit/slop.test.ts to avoid test failures.
• Consider adding documentation/comments about the new Slop signal in the public API docs.
• Run the full test suite to confirm no unrelated type errors arise from the added optional fields.

Reviewer B · nemotron-3-120b-a12b — recommends ✅ merge
The PR adds a new 'no linked issue without rationale' signal to the slop assessment with appropriate weights, rubric updates, and logic. Changes are localized to signals/engine, use existing helper functions, maintain public/private boundary (publicText uses safe language), and include comprehensive tests. Zod schemas updated backward-compatibly with optional fields. No blockers identified.

No blocking issues spotted.

[ghost]

Note

Gittensory Gate skipped

PR closed before full evaluation. No late first comment was created.

Signal	Result	Evidence	Action
Gate result	⚠️ Skipped	#962 is no longer open.	No action.

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[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.63%. Comparing base (3baa00d) to head (e4954e4).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #962   +/-   ##
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  Coverage   96.63%   96.63%           
=======================================
  Files         110      110           
  Lines       15028    15036    +8     
  Branches     5428     5433    +5     
=======================================
+ Hits        14522    14530    +8     
  Misses        104      104           
  Partials      402      402           

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[ghost]

Held for maintainer (guardrail_area) — correct + CI green