Fix repository-scoped issue trust

[mchwang]

Closes #41

Outcome

Issue trust now follows GitHub's current repository collaborator list instead of treating organization membership as repository access. author_association remains validated, visible metadata.

Reproduction

On baseline 1e59b7dfda199c8156c09a9cb9a690e5b55f1b5e, the enum-complete fixture failed because MEMBER normalized to trusted without repository-specific evidence.

Changes

• validate and retain the issue author login, distinguishing an explicit deleted author from an omitted field
• retrieve current collaborators with literal read-only arguments, bounded pagination, one overall deadline, and fail-closed validation
• classify trust from case-insensitive current collaborator membership for every author-association enum
• document the corrected trust boundary and unavailable-on-permission-failure behavior

Validation

Validated head: 9bf0c951b2855fdd9fee7b0cfdb7e4350a0ec2b6

• npm test — 15 files, 341 tests passed
• npm run typecheck — passed
• git diff --check — passed before commit; exact validated head is clean

Review rounds

• Self-review round 1: no findings after adding bounded collaborator pagination, malformed/duplicate response rejection, deleted/omitted-author handling, and the enum-complete trust matrix.
• Copilot round 1: no inline findings. Its summary concern reproduced: an early return for all-deleted authors bypassed the documented collaborator-access validation. Removed that bypass and added a failing-before/passing-after regression. Declined: none.
• Copilot round 2: no inline findings. Its summary concern reproduced at the remaining zero-issue early return, which also bypassed collaborator-access validation. Removed the final bypass and added a failing-before/passing-after empty-snapshot regression. Declined: none.
• Copilot round 3: converged with Findings: None, no inline threads, and only the expected request for final human review of the authorization-sensitive change. Changed: none. Declined: none.

Review-lesson audit

• Covered by existing rule: validate every field used to classify an external record as clear, and fail closed on malformed policy data (AGENTS.md, Guarded external actions).
• Covered by existing rule: bounded safety scans fail closed when their limit is exceeded (AGENTS.md, Guarded external actions).
• Covered by existing rule: require every safety-critical API field before an early return, including terminal-success paths (AGENTS.md, Guarded external actions).
• New reusable rule: none. This fix applies the existing repository-scoped authorization and fail-closed rules.
• One-off: GitHub MEMBER specifically means organization membership and therefore cannot itself establish repository access.

Deferred scope

• H4 issue-screen integration remains gated on G4 and is not part of this follow-up.

[Copilot]

Copilot review overview

🔵 Needs a closer look

A moderate unresolved issue weakens fail-closed behavior when no non-deleted authors are present.

Review effort: Lite
Findings: None

What changed in this PR

Updates GitHub issue trust to use current repository collaborators instead of organization membership, with validated author metadata and fail-closed handling.

Changes:

• Adds author validation and collaborator-based trust classification.
• Adds bounded collaborator pagination and malformed-response checks.
• Updates tests and documentation for the repository-scoped policy.
• Moderate unresolved finding: collaborator validation is skipped when no non-deleted authors exist.

File	Description
test/​issues.test.ts	Adds trust, pagination, and validation coverage.
test/​issue-ranking.test.ts	Updates issue fixtures with author identity.
github/​issues.ts	Implements author validation and collaborator-based trust.
docs/​implementation/​issue-prioritization.md	Documents the corrected trust boundary.

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[Copilot]

Copilot review overview

🔵 Needs a closer look

Collaborator permission failures can be silently bypassed when no issues are returned.

Review effort: Lite
Findings: None

[Copilot]

Copilot review overview

🔵 Needs a closer look

Security-sensitive authorization changes require final human review.

Review effort: Lite
Findings: None