docs(flaky-tests): document fork PR uploads via public repo identifier

[samgutentag]

Summary

Adds a new section to the Multiple Repositories and Forks page explaining how to upload test results from GitHub Actions fork PR workflows that cannot access org secrets.

The new section covers:

• Why fork PR workflows cannot use $TRUNK_API_TOKEN
• How to enable fork PR uploads in repository settings
• How to use the public repo identifier in GitHub Actions YAML
• How the authorization model works

Source

• trunk2 PR: https://github.com/trunk-io/trunk2/pull/3908

Test plan

• Check Mintlify preview link (posted on the PR by the Mintlify GitHub app)

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Project	Status	Preview	Updated (UTC)
trunk	🟢 Ready	View Preview	May 19, 2026, 6:19 PM

[samgutentag]

Verification status (May 19, 2026): pending

Eng merged but feature is not end-to-end functional for customers yet.

• Eng PR: https://github.com/trunk-io/trunk2/pull/3908
• Flag: none (no feature flag found)
• Signals:
  • trunk2#3908 merged May 18, 2026
  • Backend (legacy monolith accepting X-Trunk-Public-Repo-Id) not yet implemented (explicit out-of-scope in PR description)
  • analytics-cli support for --public-repo-id flag not yet added (explicit out-of-scope)
  • Frontend settings UI toggle is live, but the upload path is incomplete

Hold off on publishing. Re-check after the monolith and analytics-cli cross-repo TODOs are completed.

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[samgutentag]

Verification status (2026-05-19): blocked

Eng PR not merged. Hold.

• Eng PR: trunk2#3908 (merged 2026-05-18). Cross-repo deps still OPEN:
  • analytics-cli#1086 (Support X-Trunk-Public-Repo-Id auth for fork PRs)
  • trunk#31970 (Accept X-Trunk-Public-Repo-Id on flaky-tests upload + quarantine endpoints)
• Flag: none
• Signals: same blocker as PR docs(flaky-tests): document fork PR uploads per-repo opt-in #33. The customer workflow (uploading via fork PR with public-repo-id in YAML) is non-functional until analytics-cli ships the header.

Note: PR #33 also documents this feature. The two cover overlapping content; coordinate which to merge.

Label: awaiting eng.

[samgutentag]

Verification status (May 20, 2026): pending

Eng merged but the end-to-end feature is not yet complete. The trunk2 frontend and API changes merged in #3908, but the legacy monolith (api.trunk.io) and analytics-cli changes are listed as cross-repo TODOs in the PR.

• Eng PR: trunk-io/trunk2#3908 (merged 2026-05-18)
• Flag: none (no explicit LaunchDarkly flag found)
• Signals: trunk2#3908 merged; legacy monolith X-Trunk-Public-Repo-Id support pending; analytics-cli fork PR identifier pending

Hold until the cross-repo TODOs (monolith + analytics-cli) are shipped.

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