fix(github): add the Content-Length DoS pre-check to handleOrbRelay

[kai392]

Summary

handleGitHubWebhook rejects an oversized request via a content-length header check (413
fast-path) before touching the body (#197, "Harden GitHub webhook endpoint against large-body DoS").
handleOrbRelay — which processes the identical GitHub payload shape — went straight to
readBodyWithLimit, enforcing the byte cap only after buffering up to it. The two receivers diverged
on this bound with no explanation.

Adds the same content-length pre-check (413 before touching the body) to handleOrbRelay, matching
handleGitHubWebhook's existing pattern exactly.

Test plan

• New: an oversized content-length header returns 413 with a bad signature — proving the pre-check short-circuits before the body is read/verified (would be 401 otherwise)
• New: a within-cap content-length header still reaches 202 (the pre-check doesn't false-positive)
• Non-vacuity verified: removing the pre-check makes the oversized request fall through to a 401 and the 413 test fails
• npx vitest run test/unit/webhook.test.ts — 23/23 pass; tsc --noEmit clean

Closes #8888

[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 90.59%. Comparing base (469e8e6) to head (76e77ee).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8940      +/-   ##
==========================================
+ Coverage   90.56%   90.59%   +0.03%     
==========================================
  Files          96       97       +1     
  Lines       22490    22584      +94     
  Branches     3884     3914      +30     
==========================================
+ Hits        20367    20461      +94     
  Misses       1945     1945              
  Partials      178      178              

Flag	Coverage Δ
backend	100.00% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

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

[loopover-orb]

Tip

✅ LoopOver review result - approve/merge recommended

_{Review updated: 2026-07-26 14:14:31 UTC}

2 files · 1 AI reviewer · no blockers · readiness 93/100 · CI green · clean

✅ Suggested Action - Approve/Merge

• safe to merge

Review summary
This PR adds the identical Content-Length pre-check that handleGitHubWebhook already uses to handleOrbRelay, closing the gap where the relay receiver only enforced the body-size cap after buffering. The change is a straightforward copy of the existing pattern (src/github/webhook.ts:80-83 mirrored at :242-246), and the two new tests correctly prove the pre-check fires (413 with a bad signature that would otherwise yield 401) and doesn't false-positive on an in-cap request. This is a narrow, well-targeted fix tied to a real behavioral divergence between two receivers processing the same payload shape.

Nits — 5 non-blocking

• src/github/webhook.ts:80-83 and :242-246 now duplicate the same content-length pre-check logic verbatim — consider factoring it into a small shared helper (e.g. `checkContentLengthCap(header, max)`) to avoid drift if the cap logic ever changes.
• The `413` status magic number recurs at src/github/webhook.ts:244 same as the existing one at line ~82 — pre-existing pattern, not introduced here, but a named constant would help if you touch this again.
• The flagged 'secret' strings in test/unit/webhook.test.ts:696/711 are test fixture values (`orbenr_testsecret`), not real credentials — no action needed.
• Consider extracting the repeated Content-Length pre-check into a shared helper used by both handleGitHubWebhook and handleOrbRelay to keep the two receivers from re-diverging in the future.
• Possible secret-shaped assignment in the diff (generic_secret_assignment) — Verify the value is not a real credential.

Decision drivers

• ✅ Code review — No blockers (1 reviewer)
• ✅ Gate result — Passing (No configured blocker found.)

Context & advisory signals — never blocks the verdict

Signal	Result	Evidence
Linked issue	✅ Linked	#8888
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 (1 linked issue).
Validation posture	✅ 25/25	PR body includes validation/test evidence.
Contributor workload	✅ 10/10	Author activity: 133 registered-repo PR(s), 66 merged, 6 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	kai392; Gittensor profile; 133 PR(s), 6 issue(s).
Improvement	✅ Minor	risk: clean · value: minor · LLM: minor

Linked issue satisfaction

Addressed
The PR adds a content-length pre-check to handleOrbRelay that returns 413 before readBodyWithLimit is called, matching handleGitHubWebhook's pattern, and includes tests verifying both the oversized-rejection (413 vs. would-be 401) and within-cap acceptance cases.

Review context

• Author: kai392
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository is configured for direct PR review.
• Public profile languages: Python, Cuda, JavaScript, Kotlin, Perl, TypeScript, Vue
• Official Gittensor activity: 133 PR(s), 6 issue(s).
• PR-specific overlap: none found.

Contributor next steps

• Start here: Triage stale or unlinked PRs.

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.

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_{🟩 Safe / merged · 🟦 Advisory · 🟨 Held for review · 🟥 Blocked / closed}

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LoopOver approves — the gate is satisfied and CI is green.