feat(review): add cache hit/miss telemetry to grounding and review-memory (#4448)

[JSONbored]

Summary

• Two of the six AI-touching capabilities feat(stats): AI-feature cache/reuse-efficiency rate, tracked over time, public #4448 identified as having zero reuse-rate signal: grounding's per-file GitHub Contents cache (getCachedGroundingFileContent) and review-memory's in-isolate suppression-list TTL cache (getCachedReviewSuppressions, from fix(review): review-memory suppression list re-read from D1 on every comment render, no cache #4508). Both already correctly avoid redundant work — they just had no telemetry proving it, mirroring the exact gap fix(review): repo-culture-profile cache works correctly but has zero hit/miss telemetry #4509 closed for repo_culture_profile.
• Instruments both with the SAME incr() + recordAuditEvent hit/miss pair convention already established for repo_culture_profile / ai_review / ai_slop / linked_issue_satisfaction / miner_detection, so a future aggregate reuse-rate computation (feat(stats): AI-feature cache/reuse-efficiency rate, tracked over time, public #4448's remaining deliverable) can read a consistent event shape across every instrumented capability.
• New metrics: gittensory_grounding_cache_hit_total/_miss_total, gittensory_review_memory_cache_hit_total/_miss_total. New audit events: github_app.grounding_cache_hit/_miss, github_app.review_memory_cache_hit/_miss.

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.
• Advances feat(stats): AI-feature cache/reuse-efficiency rate, tracked over time, public #4448 (part of epic Epic: public, tracked-over-time benchmarks for gittensory's own review engine (speed, accuracy trend, efficiency) #4445) — a partial slice, so this does not close the issue.

Validation

• git diff --check
• npm run actionlint
• npm run typecheck
• npm run test:coverage locally — 100% branch coverage on the new telemetry code in both files (confirmed via a scoped coverage run; the only reported gaps in these two files are pre-existing functions outside this diff, exercised by other test files not included in that scoped run)
• npm run test:workers
• npm run build:mcp
• npm run test:mcp-pack
• npm run ui:openapi:check
• npm run ui:lint
• npm run ui:typecheck
• npm run ui:build
• npm audit --audit-level=moderate — 0 vulnerabilities
• New or changed behavior has unit/integration tests for new branches, fallback paths, and sanitizer boundaries — hit invariant, miss invariant, and a "swallows a failing audit-event write" fail-safe test per capability, mirroring fix(review): repo-culture-profile cache works correctly but has zero hit/miss telemetry #4509's exact test structure

Safety

• No secrets, wallet details, hotkeys, coldkeys, user PATs, private keys, raw trust scores, private rankings, or private maintainer evidence are exposed.
• Public GitHub text stays sanitized, low-noise, and does not imply compensation guarantees or optimization tactics.
• Auth, cookie, CORS, GitHub App, Cloudflare, or session changes include negative-path tests. — N/A, no auth/session surface touched.
• API/OpenAPI/MCP behavior is updated and tested where needed. — N/A, no public API surface changed in this slice (audit events are internal telemetry, not a public response).
• UI changes use live API data or real empty/error/loading states, not production mock/demo fallbacks. — N/A, backend-only change.
• Visible UI changes include a UI Evidence section. — N/A, backend-only change, no visible UI.
• Public docs/changelogs are updated where needed. — N/A, internal telemetry only, nothing public-facing yet.

Notes

• The remaining three uninstrumented capabilities (enrichment, impact-map, reputation) don't have an existing cache mechanism to instrument, unlike these two — they need their own investigation into what a meaningful "reuse signal" looks like for each, deferred to follow-up PRs. The aggregate reuse-rate computation, daily rollup, public API extension, and homepage trend chart are also deferred.

[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 94.12%. Comparing base (450e314) to head (01184aa).
⚠️ Report is 4 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4658   +/-   ##
=======================================
  Coverage   94.12%   94.12%           
=======================================
  Files         434      434           
  Lines       38496    38510   +14     
  Branches    14038    14038           
=======================================
+ Hits        36233    36247   +14     
  Misses       1604     1604           
  Partials      659      659           

Files with missing lines	Coverage Δ
src/review/grounding-wire.ts	96.73% <100.00%> (+0.26%)	⬆️
src/review/review-memory-wire.ts	100.00% <100.00%> (ø)

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Caution

🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥

🛑 Gittensory review result - fixes required

_{Review updated: 2026-07-10 10:11:30 UTC}

4 files · 1 AI reviewer · 2 blockers · readiness 93/100 · CI failing · unstable

🛑 Suggested Action - Manual Review

• No linked issue detected — If this PR is intended to solve an issue, link it explicitly in the PR body.
• Maintainer requires a linked issue — Link the relevant issue (for example Closes #123) before opening the PR.

Review summary
This adds cache hit/miss telemetry (incr() counter + recordAuditEvent) to two existing caches — the grounding file-content D1 cache in grounding-wire.ts and the in-isolate review-suppression TTL cache in review-memory-wire.ts — mirroring the established repo_culture_profile (#4509) pattern exactly. Both call sites correctly place the miss branch on the fallthrough path and wrap recordAuditEvent in .catch(() => undefined) so a failed audit write never breaks the cached-value return, which is verified by dedicated 'swallows a failing audit-event write' tests in both test files. Test coverage is thorough: hit, miss, TTL-expiry-as-miss, and audit-write-failure scenarios are all exercised with concrete assertions on both the rendered metrics text and the audit_events table.

Nits — 5 non-blocking

• grounding-wire.ts:145-153 and review-memory-wire.ts:47-55 now `await recordAuditEvent(...)` on every cache HIT before returning, adding a D1 write to a path that previously had zero I/O (review-memory) or only the cache-lookup read (grounding) — since `getFileContent` is called once per changed file, consider firing the audit write without awaiting it (fire-and-forget) to avoid serializing D1 latency into the grounding fetch loop.
• The `detail` strings duplicate what `eventType` already encodes (e.g. 'reused a cached grounding file blob instead of re-fetching from GitHub' vs `github_app.grounding_cache_hit`) — consistent with existing repo_culture_profile events, so not asking for a change, just noting the redundancy is inherited rather than new.
• grounding-wiring.test.ts's cache-hit test relies on two separate `makeGithubFileFetcher` calls sharing the same underlying D1-backed cache — worth a one-line comment (like review-memory-store.test.ts already has) clarifying the cache is keyed by (repo, path, ref) at the D1 layer, not per-fetcher-instance, so a reader doesn't assume the second fetcher instance is coincidentally warm.
• Consider whether recordAuditEvent on every cache hit is worth the write volume long-term (grounding fetches can be dozens of files per PR); if audit-event volume becomes a concern, sampling or batching could be a follow-up.
• The `/* v8 ignore next */` block in grounding-wire.ts is unrelated to this diff and can be ignored for this review.

Why this is blocked

• No linked issue detected — If this PR is intended to solve an issue, link it explicitly in the PR body.
• Maintainer requires a linked issue — Link the relevant issue (for example Closes #123) before opening the PR.

CI checks failing

• codecov/patch — 93.75% of diff hit (target 99.00%)

Signal	Result	Evidence
Code review	❌ 2 blockers	1 reviewer
Linked issue	⚠️ Missing	No linked issue or no-issue rationale found.
Related work	✅ No active overlap found	No same-issue or scoped active PR overlap found.
Change scope	✅ 20/20	Low review scope from cached public metadata (no linked issue context).
Validation posture	✅ 25/25	PR body includes validation/test evidence.
Contributor workload	✅ 10/10	Author activity: 48 registered-repo PR(s), 40 merged, 330 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	JSONbored; Gittensor profile; 48 PR(s), 330 issue(s).
Gate result	❌ Blocking	Repo-configured hard blocker found.

Review context

• Author: JSONbored
• Role context: owner (maintainer lane)
• Public audience mode: oss maintainer
• Lane context: Repository is configured for direct PR review.
• Public profile languages: not available
• Official Gittensor activity: 48 PR(s), 330 issue(s).
• PR-specific overlap: none found.

Contributor next steps

• Treat this as maintainer-lane context rather than normal contributor-lane activity.
• Explain no-issue PR.
• Link the issue being solved, or explicitly explain why this is a no-issue PR.

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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