fix(github): keep exact page-limit fetches complete instead of capped

[Dexterity104]

Summary

The REST paginator githubPaged flagged a sync segment as capped whenever a fetch ended with items.length >= limit, even when the repository had already returned its entire set in a full final page with no rel="next" link. A repo with exactly limit open issues or pull requests was reported as truncated: the public dataQuality.capped flag was set and a wasteful resume fetch was scheduled against a fabricated cursor that pointed at an empty page.

Genuine overflow is already handled inside the pagination loop, where a real next page sets status = "capped" together with its true resume cursor, so the post-loop block could only ever fire on the false positive. The fix drops the speculative cursor on a clean, fully drained fetch so an exact-limit final page stays complete. It also prevents a later resume from starting at page two and skipping page one, because githubPaged reads the stored cursor without checking the prior status.

No issue is linked: this is a small, self-contained correctness fix confined to the backfill paginator and its tests.

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
• 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 skipped. The change touches only src/github/backfill.ts and its unit tests, so the UI, MCP, and OpenAPI surfaces are unaffected and their checks pass unchanged.

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. This change is backend-only and has no visible UI, frontend, docs, or extension surface.

Notes

• Added a regression test that a repo returning exactly the page limit with no next page stays complete rather than capped, and updated the existing cap test to model genuine overflow with a real rel="next" link.
• Coverage on the changed lines is 100% for both lines and branches.

[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 95.35%. Comparing base (f160cbb) to head (5392c9e).
⚠️ Report is 3 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1385      +/-   ##
==========================================
- Coverage   95.35%   95.35%   -0.01%     
==========================================
  Files         191      191              
  Lines       20711    20709       -2     
  Branches     7488     7487       -1     
==========================================
- Hits        19750    19748       -2     
  Misses        380      380              
  Partials      581      581              

Files with missing lines	Coverage Δ
src/github/backfill.ts	92.89% <100.00%> (-0.02%)	⬇️

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