Add shared Environment GitHub Connections with access grants and reviewers #184

Parent

#181 — Applications as product containers with isolated Environments.

What to build

An Operator can establish an Environment-owned shared GitHub integration, grant explicit access to customer application users, and assign independently authenticated reviewers. An agent or Workflow requests an exact external action through that shared Connection; the Connector Gateway verifies current requester access and reviewer authority before dispatch. Existing subject-owned Connections remain supported.

Acceptance criteria

• Shared Connections belong to one Environment, have explicit shared ownership, and do not encode company or machine ownership as a fictional External Subject.
• Shared GitHub authorization is independent of a connecting employee's personal runtime identity; provider setup distinguishes user-delegated credentials from installation authority.
• Explicit Connection Access Grants determine which External Subjects may request shared-Connection operations.
• Explicit Connection Reviewer Assignments determine who may approve writes; a requester can approve only when also assigned as a reviewer.
• One authorized human reviewer approves the exact canonical Action Intent digest; modified target or payload requires fresh approval.
• Environment keys may request authorized work but cannot impersonate human reviewer participation or alter identity trust.
• Grant, reviewer, subject, Connection and Environment revocation before dispatch prevent stale authority; a claimed external write reports its actual or unknown outcome without unsafe reposting.
• Disabling Alice prevents her use while preserving the shared integration for other explicitly authorized subjects.
• Personal Connections retain owner-only exact-action consent.
• Setup, grants, reviewers and approval outcomes are manageable through the API/SDK and authorized web controls.
• Unauthorized use, cross-Environment access, stale reviewer consent and revocation races are verified at existing real-database API and Connector Gateway seams.
• Lint, typecheck, formatting, generated contracts and affected launch/integration gates pass.

Blocked by

#183 — Application ownership and isolated Environment deployments.