feat(selfhost): use conditional REST validators for backfill segments

[oktofeesh1]

Summary

• Adds conditional REST validator support to queued open-data backfill segment reads.
• Handles 304 Not Modified as a fresh terminal segment while preserving counts, cursors, validators, and current-open scan markers.
• No issue because this is a narrow self-hosted backfill optimization with no schema, config, UI, or deployment-surface change.

Scope

• The PR title follows type(scope): short summary Conventional Commit format, for example fix(api): restore profile access checks.
• 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.
• I linked an issue, or this is small enough that the summary explains why an issue is not needed.

Validation

• git diff --check
• npm run actionlint
• npm run typecheck
• npm run test:coverage locally; codecov/patch requires ≥97% coverage of the lines AND branches you changed (aim for 98%+ on your diff so CI variance does not fail near the threshold). Global coverage is a non-blocking trend with a loose 90% backstop, not the gate.
• 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
• New or changed behavior has unit/integration tests for new branches, fallback paths, and sanitizer boundaries

If any required check was skipped, explain why:

• None. npm run test:ci passed after rebasing on upstream main; the scoped test/unit/backfill.test.ts suite also passed.

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.
• API/OpenAPI/MCP behavior is updated and tested where needed.
• UI changes use live API data or real empty/error/loading states, not production mock/demo fallbacks.
• Visible UI changes include a UI Evidence section below with JPG/JPEG or PNG screenshots arranged as organized, captioned, clickable thumbnails. SVG screenshots are not used as review evidence. Review-only screenshots or recordings are not committed to the repository.
• Public docs/changelogs are updated where needed; changelogs are only edited for release-prep PRs.

UI Evidence

Not applicable; backend-only queue/backfill behavior change.

Notes

• Reuses stored ETag / Last-Modified values only for safe single-page segment validation.
• Keeps current-open scan resume markers intact by using Last-Modified instead of replaying the marker as an ETag.
• Treats not-modified segments as fresh in repository sync state and still schedules PR detail hydration for unchanged open PR lists.

[loopover-orb]

Warning

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⏸️ Gittensory review result - manual review recommended

_{Review updated: 2026-06-30 23:44:08 UTC}

2 files · 1 AI reviewer · no blockers · readiness 73/100 · CI green · unknown

⏸️ Suggested Action - Manual Review

• Touches a guarded path — held for manual review

Review summary
This change adds conditional REST validators to single-page backfill segment reads and treats 304 responses as fresh terminal segment rows while preserving prior counts, cursors, and validators. The visible implementation is coherent: it gates conditional requests to fresh single-page segments, avoids sending the current-open marker as an ETag, and refreshes repo sync timestamps for not_modified rows. The added tests exercise the important paths: initial 200, 304 reuse, unauthenticated fallback, changed totals, and paginated-segment bypass.

Nits — 6 non-blocking

• nit: src/github/backfill.ts:1260 relies on lastCursor/nextCursor to identify a single-page segment but does not also require previous.pageCount === 1, so an inconsistent stored row could still send validators when the stored page count says otherwise.
• nit: src/github/backfill.ts:1320 intentionally uses Last-Modified-only validation for current-open PR scans because the ETag column stores the current-open marker; that is worth a short comment because it is weaker than the ETag path and easy to misread later.
• In src/github/backfill.ts:1260, add previous.pageCount === 1 to conditionalRequestForSegment so the eligibility check matches the stated single-page invariant directly.
• In src/github/backfill.ts:1320, document why current-open scans cannot send If-None-Match here, or split the marker from the stored REST validator in a follow-up so current-open scans can use ETags too.
• 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	✅ No-issue rationale	PR body explains why no issue is linked.
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 (size label size:L; no linked issue context).
Validation posture	❌ 5/25	Preflight is holding this PR; address the blocker before review.
Contributor workload	✅ 10/10	Author activity: 73 registered-repo PR(s), 61 merged, 6 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	oktofeesh1; Gittensor profile; 73 PR(s), 6 issue(s).
Gate result	⚠️ Not blocking	Advisory; not blocking this PR.

Review context

• Author: oktofeesh1
• 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: 73 PR(s), 6 issue(s).
• PR-specific overlap: none found.

Contributor next steps

• 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.

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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