fix(selfhost): send conditional backfill requests on the scheduled cadence (#1942)

[JSONbored]

Summary

#1901 added conditional (ETag / If-Modified-Since) validators for backfill segments, but fetchPagedSegment only loaded the prior segment row — and thus only built the conditional request — when mode === "resume" (src/github/backfill.ts:1289). The scheduled cadence runs in light/full mode, so the 304 fast-path never fired on the path that actually runs: every 30-min light crawl re-listed labels / open-issues / open-PRs at full cost even when nothing had changed.

This loads the prior segment for every mode, so a scheduled light/full crawl sends the stored If-None-Match and an unchanged single-page list returns a 0-body 304 instead of a full re-list — the largest avoidable GitHub cost on the backfill cadence.

Correctness is preserved by the machinery that was already there:

• Resume pagination stays gated on canResumePreviousScan (mode === "resume"), so light/full still start a fresh page-1 scan — only the conditional header is added.
• The open-scan segments that must reconcile GitHub-side closes still force allowEtag: false, so they always full-scan; loading previous never lets a dropped close slip through.
• conditionalRequestForSegment still requires the prior scan to be fresh, complete, single-page, and expectedCount-matched before sending validators.

Advances #1942 (rec #3 from the #1936 audit); builds directly on #1901.

Scope

• Conventional Commit title.
• Focused, backend-only change.
• Follows CONTRIBUTING.md; no site//CNAME.
• Linked issue (advances fix(queue): eliminate duplicate scheduled work and gate jitter #1942).

Validation

• git diff --check
• npm run typecheck
• npm run test:coverage — the single changed line is exercised by the existing backfill segment suite (133 tests); added a regression test proving the light cadence now sends If-None-Match and short-circuits to not_modified (it asserts status: "complete" → not_modified and the exact request headers, so it fails without the fix).
• npm run test:ci
• npm audit --audit-level=moderate

If any required check was skipped, explain why:

• No ui:openapi / cf-typegen / migration regen: single-file backend change, no API/schema/binding/DB change.

Safety

• No secrets/wallets/hotkeys/trust-scores/etc.
• Public GitHub text unchanged.
• No auth/CORS/session change.
• No API/OpenAPI/MCP change. No UI change.

Notes

• The only behavior change is that light/full crawls now send conditional headers; the open-scan/reconciliation segments are unaffected (allowEtag: false), so close-detection is unchanged.

[loopover-orb]

Warning

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⏸️ Gittensory review result - manual review recommended

_{Review updated: 2026-07-01 04:06:25 UTC}

2 files · 1 AI reviewer · no blockers · readiness 68/100 · CI green · clean

⏸️ Suggested Action - Manual Review

• Touches a guarded path — held for manual review

Review summary
This change moves prior segment loading out of resume-only mode so the existing conditional-request logic can run on scheduled light/full segment crawls while leaving resume pagination gated by `canResumePreviousScan`. The added regression test exercises the real `backfillRepositorySegment` light-mode path twice and verifies that the second labels request carries the stored validators and returns `not_modified`, which directly covers the bug described. I do not see a reachable correctness break in the visible diff.

Nits — 6 non-blocking

• nit: `src/github/backfill.ts:1286` adds a five-line explanatory comment that mostly repeats the PR description; keeping only the invariant that matters locally would make this easier to maintain.
• nit: `test/unit/backfill.test.ts:1288` packs the GraphQL totals response into a long single line; split it for readability alongside the rest of the test file.
• In `src/github/backfill.ts:1286`, trim the comment to the local contract: prior segment is loaded for validators in every mode, while resume pagination remains gated below and open reconciliation paths disable ETags.
• In `test/unit/backfill.test.ts:1288`, format the `githubTotalsResponse` object over multiple lines so the labels-only scenario is easier to scan.
• 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	⚠️ 1 scoped overlap	Top overlaps are listed below; lower-confidence bulk is hidden.
Change scope	❌ 8/20	High review scope from cached public metadata (size label size:XS; no linked issue context).
Validation posture	✅ 25/25	PR body includes validation/test evidence.
Contributor workload	✅ 10/10	Author activity: 68 registered-repo PR(s), 58 merged, 274 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	JSONbored; Gittensor profile; 68 PR(s), 274 issue(s).
Gate result	⚠️ Not blocking	Advisory; not blocking this PR.

Review context

• Author: JSONbored
• Role context: owner (maintainer lane)
• 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: 68 PR(s), 274 issue(s).
• Related work: Titles/paths share 5 meaningful terms. (PR #1933)

Contributor next steps

• Treat this as maintainer-lane context rather than normal contributor-lane activity.
• Explain no-issue PR.
• Review top overlaps.
• Add a concise scope and risk note.
• Triage stale or unlinked PRs.
• No action.
• 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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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.57%. Comparing base (9e2f533) to head (945149d).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1976   +/-   ##
=======================================
  Coverage   95.57%   95.57%           
=======================================
  Files         218      218           
  Lines       24257    24257           
  Branches     8795     8794    -1     
=======================================
  Hits        23184    23184           
  Misses        436      436           
  Partials      637      637           

Files with missing lines	Coverage Δ
src/github/backfill.ts	94.65% <100.00%> (ø)

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