feat(scoring): surface the time-decay multiplier in the score breakdown

[RenzoMXD]

Summary

explainScoreBreakdown (src/services/score-breakdown.ts) explained every other scoring multiplier -- density, contribution bonus, label, issue, credibility, review penalty, open-PR pressure, open-issue spam, the merged-PR history floor (added by #1801), and now the issue-discovery validity floor (added by #1874) -- but silently omitted the timeDecayMultiplier, even though it multiplies into the final score (preview.ts:432) and is the only remaining multiplier on scoreEstimate without a breakdown component.

What this adds

A timeDecayBreakdown component mirroring the sibling mergedHistoryBreakdown (#1801) and issueDiscoveryHistoryBreakdown (#1874):

• neutral when the multiplier is >= 0.99 (the PR is fresh, or upstream time-decay -- env SCORING_TIME_DECAY_ENABLED, default OFF -- is disabled for the preview). The summary explicitly surfaces the env flag so a contributor understands why there is no age penalty on their preview.
• reduced (or further) with an aged-PR lever ("land the work while it is fresh, or extend the upstream time-decay curve in the repo's master_repositories.json override for this repo to slow the decay") when the multiplier has decayed -- purely upstream-sigmoid curve at preview.ts:1265.

Purely additive explanation; no scoring behavior change.

Scope

• The PR title follows type(scope): short summary Conventional Commit format.
• This PR is focused and does not mix unrelated backend, UI, MCP, docs, dependency, and deploy changes.
• This follows CONTRIBUTING.md and does not reintroduce GitHub Pages, VitePress, site/, or CNAME.
• No linked issue -- this is a small, self-evident additive feat that completes the time-decay surface next to feat(scoring): surface the merged-PR history floor in the score breakdown #1801 and feat(scoring): surface the issue-discovery validity floor in the score breakdown #1874. The contributor fork PAT used here does not have upstream issue-create scope, and an unlinked PR is an explicitly allowed submission pattern per the contributing guide.

Validation

• git diff --check
• npm run actionlint
• npm run typecheck
• npm run test:coverage -- test/unit/score-breakdown.test.ts 12/12 pass; src/services/score-breakdown.ts is 100% statements / 100% functions / 100% lines (the new component's two branches -- fresh / disabled and aged-with-decay -- are each covered).

Targeted run:

npx vitest run test/unit/score-breakdown.test.ts --coverage --coverage.include='src/services/score-breakdown.ts'
# 12/12 passed; 100% statements/functions/lines

Safety

• No secrets, wallet details, hotkeys, coldkeys, user PATs, private keys, raw trust scores, private rankings, or private maintainer evidence are exposed (a forbidden-term assertion is included).
• Public GitHub text stays sanitized, low-noise, and does not imply compensation guarantees or optimization tactics (every summary/lever runs through the existing sanitizePublicComment).
• No auth, cookie, CORS, GitHub App, Cloudflare, or session changes -- a purely additive explanation projection over an already-computed multiplier; no scoring logic change.
• No UI changes.
• No docs/changelog changes.

UI Evidence

Not applicable -- backend score-breakdown projection with no visible UI, frontend, docs, or extension surface.

[gittensory-orb]

Warning

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⏸️ Gittensory review result - manual review recommended

_{Review updated: 2026-06-30 19:12:12 UTC}

2 files · 1 AI reviewer · no blockers · readiness 48/100 · CI green · unknown

⏸️ Suggested Action - Manual Review

• Touches a guarded path — held for manual review

Review summary
The diff cleanly adds `timeDecayMultiplier` to the score-breakdown component list and sanitizes it through the same path as the existing multiplier explanations. The new helper mirrors the surrounding breakdown functions, covers both neutral and decayed cases, and the test asserts the component is present plus exercises the reduced branch through `buildScorePreview`. I do not see a reachable correctness break in the provided changed files.

Nits — 7 non-blocking

• nit: `src/services/score-breakdown.ts:144` uses one neutral summary for two materially different states, so a fresh PR and disabled time decay are indistinguishable to the reader; consider using available preview/input state if exposed, or soften the wording further.
• nit: `src/services/score-breakdown.ts:153` hard-codes curve details in the public explanation, which can drift if the upstream sigmoid constants change; consider deriving those values from the scoring constants or keeping the summary less parameter-specific.
• nit: `test/unit/score-breakdown.test.ts:165` only asserts the neutral band for the fresh/disabled case and does not verify the new explanatory text is sanitized/non-empty in that branch specifically.
• In `src/services/score-breakdown.ts:144`, split the neutral explanation if the preview model exposes whether decay was disabled versus merely still inside the grace period.
• In `src/services/score-breakdown.ts:153`, avoid embedding exact curve constants unless they are sourced from the same scoring configuration that calculates `timeDecayMultiplier`.
• Readiness score is below the configured threshold — Use the readiness panel as advisory maintainer context; the score does not block this PR.
• Touches a guarded path — held for manual review — A maintainer must review and merge this change.

Signal	Result	Evidence
Code review	✅ No blockers	1 reviewer
Linked issue	⚠️ Missing	No linked issue or no-issue rationale found.
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:S; no linked issue context).
Validation posture	❌ 5/25	Preflight is holding this PR; address the blocker before review.
Contributor workload	✅ 10/10	Author activity: 53 registered-repo PR(s), 25 merged, 7 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	RenzoMXD; Gittensor profile; 53 PR(s), 7 issue(s).
Gate result	⚠️ Not blocking	Advisory; not blocking this PR.

Review context

• Author: RenzoMXD
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository registration is not available in the local Gittensory cache.
• Public profile languages: TypeScript, Python, Rust, C++, JavaScript, Scala, Clojure, Go
• Official Gittensor activity: 53 PR(s), 7 issue(s).
• Related work: Items reference the same linked issue feat(enrichment): Churn-hotspot + bug-density scorer #1513. (issue #1513, PR #1882)
• Related work: Open PR work references issue feat(enrichment): Churn-hotspot + bug-density scorer #1513. (issue #1513, PR #1882)
• Related work: Titles/paths share 5 meaningful terms. (issue #1477, PR #1882)
• Additional title-only matches omitted; title-only overlap does not block.

Contributor next steps

• Explain no-issue PR.
• 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.
• Link the issue being solved, or explicitly explain why this is a no-issue PR.
• 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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